diff --git a/java/Android.bp b/java/Android.bp
index c67379c..b6c14ac 100644
--- a/java/Android.bp
+++ b/java/Android.bp
@@ -38,6 +38,7 @@
         "dexpreopt_bootjars.go",
         "dexpreopt_config.go",
         "droiddoc.go",
+        "droidstubs.go",
         "gen.go",
         "genrule.go",
         "hiddenapi.go",
@@ -72,6 +73,8 @@
         "device_host_converter_test.go",
         "dexpreopt_test.go",
         "dexpreopt_bootjars_test.go",
+        "droiddoc_test.go",
+        "droidstubs_test.go",
         "hiddenapi_singleton_test.go",
         "java_test.go",
         "jdeps_test.go",
diff --git a/java/droiddoc.go b/java/droiddoc.go
index 0becb84..a8e2b0e 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -23,12 +23,10 @@
 
 	"android/soong/android"
 	"android/soong/java/config"
-	"android/soong/remoteexec"
 )
 
 func init() {
 	RegisterDocsBuildComponents(android.InitRegistrationContext)
-	RegisterStubsBuildComponents(android.InitRegistrationContext)
 }
 
 func RegisterDocsBuildComponents(ctx android.RegistrationContext) {
@@ -41,19 +39,6 @@
 	ctx.RegisterModuleType("javadoc_host", JavadocHostFactory)
 }
 
-func RegisterStubsBuildComponents(ctx android.RegistrationContext) {
-	ctx.RegisterModuleType("stubs_defaults", StubsDefaultsFactory)
-
-	ctx.RegisterModuleType("droidstubs", DroidstubsFactory)
-	ctx.RegisterModuleType("droidstubs_host", DroidstubsHostFactory)
-
-	ctx.RegisterModuleType("prebuilt_stubs_sources", PrebuiltStubsSourcesFactory)
-}
-
-var (
-	srcsLibTag = dependencyTag{name: "sources from javalib"}
-)
-
 type JavadocProperties struct {
 	// list of source files used to compile the Java module.  May be .java, .logtags, .proto,
 	// or .aidl files.
@@ -177,80 +162,6 @@
 	Compat_config *string `android:"path"`
 }
 
-type DroidstubsProperties struct {
-	// The generated public API filename by Metalava, defaults to <module>_api.txt
-	Api_filename *string
-
-	// the generated removed API filename by Metalava, defaults to <module>_removed.txt
-	Removed_api_filename *string
-
-	// the generated removed Dex API filename by Metalava.
-	Removed_dex_api_filename *string
-
-	Check_api struct {
-		Last_released ApiToCheck
-
-		Current ApiToCheck
-
-		Api_lint struct {
-			Enabled *bool
-
-			// If set, performs api_lint on any new APIs not found in the given signature file
-			New_since *string `android:"path"`
-
-			// If not blank, path to the baseline txt file for approved API lint violations.
-			Baseline_file *string `android:"path"`
-		}
-	}
-
-	// user can specify the version of previous released API file in order to do compatibility check.
-	Previous_api *string `android:"path"`
-
-	// is set to true, Metalava will allow framework SDK to contain annotations.
-	Annotations_enabled *bool
-
-	// a list of top-level directories containing files to merge qualifier annotations (i.e. those intended to be included in the stubs written) from.
-	Merge_annotations_dirs []string
-
-	// a list of top-level directories containing Java stub files to merge show/hide annotations from.
-	Merge_inclusion_annotations_dirs []string
-
-	// a file containing a list of classes to do nullability validation for.
-	Validate_nullability_from_list *string
-
-	// a file containing expected warnings produced by validation of nullability annotations.
-	Check_nullability_warnings *string
-
-	// if set to true, allow Metalava to generate doc_stubs source files. Defaults to false.
-	Create_doc_stubs *bool
-
-	// if set to true, cause Metalava to output Javadoc comments in the stubs source files. Defaults to false.
-	// Has no effect if create_doc_stubs: true.
-	Output_javadoc_comments *bool
-
-	// if set to false then do not write out stubs. Defaults to true.
-	//
-	// TODO(b/146727827): Remove capability when we do not need to generate stubs and API separately.
-	Generate_stubs *bool
-
-	// if set to true, provides a hint to the build system that this rule uses a lot of memory,
-	// whicih can be used for scheduling purposes
-	High_mem *bool
-
-	// is set to true, Metalava will allow framework SDK to contain API levels annotations.
-	Api_levels_annotations_enabled *bool
-
-	// the dirs which Metalava extracts API levels annotations from.
-	Api_levels_annotations_dirs []string
-
-	// the filename which Metalava extracts API levels annotations from. Defaults to android.jar.
-	Api_levels_jar_filename *string
-
-	// if set to true, collect the values used by the Dev tools and
-	// write them in files packaged with the SDK. Defaults to false.
-	Write_sdk_values *bool
-}
-
 //
 // Common flags passed down to build rule
 //
@@ -947,669 +858,9 @@
 }
 
 //
-// Droidstubs
-//
-type Droidstubs struct {
-	Javadoc
-	android.SdkBase
-
-	properties              DroidstubsProperties
-	apiFile                 android.WritablePath
-	apiXmlFile              android.WritablePath
-	lastReleasedApiXmlFile  android.WritablePath
-	privateApiFile          android.WritablePath
-	removedApiFile          android.WritablePath
-	removedDexApiFile       android.WritablePath
-	nullabilityWarningsFile android.WritablePath
-
-	checkCurrentApiTimestamp      android.WritablePath
-	updateCurrentApiTimestamp     android.WritablePath
-	checkLastReleasedApiTimestamp android.WritablePath
-	apiLintTimestamp              android.WritablePath
-	apiLintReport                 android.WritablePath
-
-	checkNullabilityWarningsTimestamp android.WritablePath
-
-	annotationsZip android.WritablePath
-	apiVersionsXml android.WritablePath
-
-	apiFilePath        android.Path
-	removedApiFilePath android.Path
-
-	metadataZip android.WritablePath
-	metadataDir android.WritablePath
-}
-
-// droidstubs passes sources files through Metalava to generate stub .java files that only contain the API to be
-// documented, filtering out hidden classes and methods.  The resulting .java files are intended to be passed to
-// a droiddoc module to generate documentation.
-func DroidstubsFactory() android.Module {
-	module := &Droidstubs{}
-
-	module.AddProperties(&module.properties,
-		&module.Javadoc.properties)
-
-	InitDroiddocModule(module, android.HostAndDeviceSupported)
-	android.InitSdkAwareModule(module)
-	return module
-}
-
-// droidstubs_host passes sources files through Metalava to generate stub .java files that only contain the API
-// to be documented, filtering out hidden classes and methods.  The resulting .java files are intended to be
-// passed to a droiddoc_host module to generate documentation.  Use a droidstubs_host instead of a droidstubs
-// module when symbols needed by the source files are provided by java_library_host modules.
-func DroidstubsHostFactory() android.Module {
-	module := &Droidstubs{}
-
-	module.AddProperties(&module.properties,
-		&module.Javadoc.properties)
-
-	InitDroiddocModule(module, android.HostSupported)
-	return module
-}
-
-func (d *Droidstubs) OutputFiles(tag string) (android.Paths, error) {
-	switch tag {
-	case "":
-		return android.Paths{d.stubsSrcJar}, nil
-	case ".docs.zip":
-		return android.Paths{d.docZip}, nil
-	case ".api.txt", android.DefaultDistTag:
-		// This is the default dist path for dist properties that have no tag property.
-		return android.Paths{d.apiFilePath}, nil
-	case ".removed-api.txt":
-		return android.Paths{d.removedApiFilePath}, nil
-	case ".annotations.zip":
-		return android.Paths{d.annotationsZip}, nil
-	case ".api_versions.xml":
-		return android.Paths{d.apiVersionsXml}, nil
-	default:
-		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
-	}
-}
-
-func (d *Droidstubs) ApiFilePath() android.Path {
-	return d.apiFilePath
-}
-
-func (d *Droidstubs) RemovedApiFilePath() android.Path {
-	return d.removedApiFilePath
-}
-
-func (d *Droidstubs) StubsSrcJar() android.Path {
-	return d.stubsSrcJar
-}
-
-func (d *Droidstubs) DepsMutator(ctx android.BottomUpMutatorContext) {
-	d.Javadoc.addDeps(ctx)
-
-	if len(d.properties.Merge_annotations_dirs) != 0 {
-		for _, mergeAnnotationsDir := range d.properties.Merge_annotations_dirs {
-			ctx.AddDependency(ctx.Module(), metalavaMergeAnnotationsDirTag, mergeAnnotationsDir)
-		}
-	}
-
-	if len(d.properties.Merge_inclusion_annotations_dirs) != 0 {
-		for _, mergeInclusionAnnotationsDir := range d.properties.Merge_inclusion_annotations_dirs {
-			ctx.AddDependency(ctx.Module(), metalavaMergeInclusionAnnotationsDirTag, mergeInclusionAnnotationsDir)
-		}
-	}
-
-	if len(d.properties.Api_levels_annotations_dirs) != 0 {
-		for _, apiLevelsAnnotationsDir := range d.properties.Api_levels_annotations_dirs {
-			ctx.AddDependency(ctx.Module(), metalavaAPILevelsAnnotationsDirTag, apiLevelsAnnotationsDir)
-		}
-	}
-}
-
-func (d *Droidstubs) stubsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand, stubsDir android.OptionalPath) {
-	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
-		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
-		String(d.properties.Api_filename) != "" {
-		filename := proptools.StringDefault(d.properties.Api_filename, ctx.ModuleName()+"_api.txt")
-		d.apiFile = android.PathForModuleOut(ctx, filename)
-		cmd.FlagWithOutput("--api ", d.apiFile)
-		d.apiFilePath = d.apiFile
-	} else if sourceApiFile := proptools.String(d.properties.Check_api.Current.Api_file); sourceApiFile != "" {
-		// If check api is disabled then make the source file available for export.
-		d.apiFilePath = android.PathForModuleSrc(ctx, sourceApiFile)
-	}
-
-	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
-		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
-		String(d.properties.Removed_api_filename) != "" {
-		filename := proptools.StringDefault(d.properties.Removed_api_filename, ctx.ModuleName()+"_removed.txt")
-		d.removedApiFile = android.PathForModuleOut(ctx, filename)
-		cmd.FlagWithOutput("--removed-api ", d.removedApiFile)
-		d.removedApiFilePath = d.removedApiFile
-	} else if sourceRemovedApiFile := proptools.String(d.properties.Check_api.Current.Removed_api_file); sourceRemovedApiFile != "" {
-		// If check api is disabled then make the source removed api file available for export.
-		d.removedApiFilePath = android.PathForModuleSrc(ctx, sourceRemovedApiFile)
-	}
-
-	if String(d.properties.Removed_dex_api_filename) != "" {
-		d.removedDexApiFile = android.PathForModuleOut(ctx, String(d.properties.Removed_dex_api_filename))
-		cmd.FlagWithOutput("--removed-dex-api ", d.removedDexApiFile)
-	}
-
-	if Bool(d.properties.Write_sdk_values) {
-		d.metadataDir = android.PathForModuleOut(ctx, "metadata")
-		cmd.FlagWithArg("--sdk-values ", d.metadataDir.String())
-	}
-
-	if stubsDir.Valid() {
-		if Bool(d.properties.Create_doc_stubs) {
-			cmd.FlagWithArg("--doc-stubs ", stubsDir.String())
-		} else {
-			cmd.FlagWithArg("--stubs ", stubsDir.String())
-			if !Bool(d.properties.Output_javadoc_comments) {
-				cmd.Flag("--exclude-documentation-from-stubs")
-			}
-		}
-	}
-}
-
-func (d *Droidstubs) annotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
-	if Bool(d.properties.Annotations_enabled) {
-		cmd.Flag("--include-annotations")
-
-		validatingNullability :=
-			android.InList("--validate-nullability-from-merged-stubs", d.Javadoc.args) ||
-				String(d.properties.Validate_nullability_from_list) != ""
-
-		migratingNullability := String(d.properties.Previous_api) != ""
-		if migratingNullability {
-			previousApi := android.PathForModuleSrc(ctx, String(d.properties.Previous_api))
-			cmd.FlagWithInput("--migrate-nullness ", previousApi)
-		}
-
-		if s := String(d.properties.Validate_nullability_from_list); s != "" {
-			cmd.FlagWithInput("--validate-nullability-from-list ", android.PathForModuleSrc(ctx, s))
-		}
-
-		if validatingNullability {
-			d.nullabilityWarningsFile = android.PathForModuleOut(ctx, ctx.ModuleName()+"_nullability_warnings.txt")
-			cmd.FlagWithOutput("--nullability-warnings-txt ", d.nullabilityWarningsFile)
-		}
-
-		d.annotationsZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"_annotations.zip")
-		cmd.FlagWithOutput("--extract-annotations ", d.annotationsZip)
-
-		if len(d.properties.Merge_annotations_dirs) != 0 {
-			d.mergeAnnoDirFlags(ctx, cmd)
-		}
-
-		// TODO(tnorbye): find owners to fix these warnings when annotation was enabled.
-		cmd.FlagWithArg("--hide ", "HiddenTypedefConstant").
-			FlagWithArg("--hide ", "SuperfluousPrefix").
-			FlagWithArg("--hide ", "AnnotationExtraction")
-	}
-}
-
-func (d *Droidstubs) mergeAnnoDirFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
-	ctx.VisitDirectDepsWithTag(metalavaMergeAnnotationsDirTag, func(m android.Module) {
-		if t, ok := m.(*ExportedDroiddocDir); ok {
-			cmd.FlagWithArg("--merge-qualifier-annotations ", t.dir.String()).Implicits(t.deps)
-		} else {
-			ctx.PropertyErrorf("merge_annotations_dirs",
-				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
-		}
-	})
-}
-
-func (d *Droidstubs) inclusionAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
-	ctx.VisitDirectDepsWithTag(metalavaMergeInclusionAnnotationsDirTag, func(m android.Module) {
-		if t, ok := m.(*ExportedDroiddocDir); ok {
-			cmd.FlagWithArg("--merge-inclusion-annotations ", t.dir.String()).Implicits(t.deps)
-		} else {
-			ctx.PropertyErrorf("merge_inclusion_annotations_dirs",
-				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
-		}
-	})
-}
-
-func (d *Droidstubs) apiLevelsAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
-	if !Bool(d.properties.Api_levels_annotations_enabled) {
-		return
-	}
-
-	d.apiVersionsXml = android.PathForModuleOut(ctx, "api-versions.xml")
-
-	if len(d.properties.Api_levels_annotations_dirs) == 0 {
-		ctx.PropertyErrorf("api_levels_annotations_dirs",
-			"has to be non-empty if api levels annotations was enabled!")
-	}
-
-	cmd.FlagWithOutput("--generate-api-levels ", d.apiVersionsXml)
-	cmd.FlagWithInput("--apply-api-levels ", d.apiVersionsXml)
-	cmd.FlagWithArg("--current-version ", ctx.Config().PlatformSdkVersion().String())
-	cmd.FlagWithArg("--current-codename ", ctx.Config().PlatformSdkCodename())
-
-	filename := proptools.StringDefault(d.properties.Api_levels_jar_filename, "android.jar")
-
-	ctx.VisitDirectDepsWithTag(metalavaAPILevelsAnnotationsDirTag, func(m android.Module) {
-		if t, ok := m.(*ExportedDroiddocDir); ok {
-			for _, dep := range t.deps {
-				if strings.HasSuffix(dep.String(), filename) {
-					cmd.Implicit(dep)
-				}
-			}
-			cmd.FlagWithArg("--android-jar-pattern ", t.dir.String()+"/%/public/"+filename)
-		} else {
-			ctx.PropertyErrorf("api_levels_annotations_dirs",
-				"module %q is not a metalava api-levels-annotations dir", ctx.OtherModuleName(m))
-		}
-	})
-}
-
-func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersion javaVersion, srcs android.Paths,
-	srcJarList android.Path, bootclasspath, classpath classpath, sourcepaths android.Paths,
-	implicitsRsp, homeDir android.WritablePath, sandbox bool) *android.RuleBuilderCommand {
-	rule.Command().Text("rm -rf").Flag(homeDir.String())
-	rule.Command().Text("mkdir -p").Flag(homeDir.String())
-
-	cmd := rule.Command()
-	cmd.FlagWithArg("ANDROID_PREFS_ROOT=", homeDir.String())
-
-	if ctx.Config().UseRBE() && ctx.Config().IsEnvTrue("RBE_METALAVA") {
-		rule.Remoteable(android.RemoteRuleSupports{RBE: true})
-		pool := ctx.Config().GetenvWithDefault("RBE_METALAVA_POOL", "metalava")
-		execStrategy := ctx.Config().GetenvWithDefault("RBE_METALAVA_EXEC_STRATEGY", remoteexec.LocalExecStrategy)
-		labels := map[string]string{"type": "compile", "lang": "java", "compiler": "metalava"}
-		if !sandbox {
-			execStrategy = remoteexec.LocalExecStrategy
-			labels["shallow"] = "true"
-		}
-		inputs := []string{
-			ctx.Config().HostJavaToolPath(ctx, "metalava").String(),
-			homeDir.String(),
-		}
-		if v := ctx.Config().Getenv("RBE_METALAVA_INPUTS"); v != "" {
-			inputs = append(inputs, strings.Split(v, ",")...)
-		}
-		cmd.Text((&remoteexec.REParams{
-			Labels:               labels,
-			ExecStrategy:         execStrategy,
-			Inputs:               inputs,
-			RSPFiles:             []string{implicitsRsp.String()},
-			ToolchainInputs:      []string{config.JavaCmd(ctx).String()},
-			Platform:             map[string]string{remoteexec.PoolKey: pool},
-			EnvironmentVariables: []string{"ANDROID_PREFS_ROOT"},
-		}).NoVarTemplate(ctx.Config().RBEWrapper()))
-	}
-
-	cmd.BuiltTool("metalava").
-		Flag(config.JavacVmFlags).
-		Flag("-J--add-opens=java.base/java.util=ALL-UNNAMED").
-		FlagWithArg("-encoding ", "UTF-8").
-		FlagWithArg("-source ", javaVersion.String()).
-		FlagWithRspFileInputList("@", android.PathForModuleOut(ctx, "metalava.rsp"), srcs).
-		FlagWithInput("@", srcJarList)
-
-	if javaHome := ctx.Config().Getenv("ANDROID_JAVA_HOME"); javaHome != "" {
-		cmd.Implicit(android.PathForSource(ctx, javaHome))
-	}
-
-	if sandbox {
-		cmd.FlagWithOutput("--strict-input-files ", android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"violations.txt"))
-	} else {
-		cmd.FlagWithOutput("--strict-input-files:warn ", android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"violations.txt"))
-	}
-
-	if implicitsRsp != nil {
-		cmd.FlagWithArg("--strict-input-files-exempt ", "@"+implicitsRsp.String())
-	}
-
-	if len(bootclasspath) > 0 {
-		cmd.FlagWithInputList("-bootclasspath ", bootclasspath.Paths(), ":")
-	}
-
-	if len(classpath) > 0 {
-		cmd.FlagWithInputList("-classpath ", classpath.Paths(), ":")
-	}
-
-	if len(sourcepaths) > 0 {
-		cmd.FlagWithList("-sourcepath ", sourcepaths.Strings(), ":")
-	} else {
-		cmd.FlagWithArg("-sourcepath ", `""`)
-	}
-
-	cmd.Flag("--no-banner").
-		Flag("--color").
-		Flag("--quiet").
-		Flag("--format=v2").
-		FlagWithArg("--repeat-errors-max ", "10").
-		FlagWithArg("--hide ", "UnresolvedImport")
-
-	return cmd
-}
-
-func (d *Droidstubs) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	deps := d.Javadoc.collectDeps(ctx)
-
-	javaVersion := getJavaVersion(ctx, String(d.Javadoc.properties.Java_version), sdkContext(d))
-
-	// Create rule for metalava
-
-	srcJarDir := android.PathForModuleOut(ctx, "srcjars")
-
-	rule := android.NewRuleBuilder(pctx, ctx)
-
-	if BoolDefault(d.properties.High_mem, false) {
-		// This metalava run uses lots of memory, restrict the number of metalava jobs that can run in parallel.
-		rule.HighMem()
-	}
-
-	generateStubs := BoolDefault(d.properties.Generate_stubs, true)
-	var stubsDir android.OptionalPath
-	if generateStubs {
-		d.Javadoc.stubsSrcJar = android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"stubs.srcjar")
-		stubsDir = android.OptionalPathForPath(android.PathForModuleOut(ctx, "stubsDir"))
-		rule.Command().Text("rm -rf").Text(stubsDir.String())
-		rule.Command().Text("mkdir -p").Text(stubsDir.String())
-	}
-
-	srcJarList := zipSyncCmd(ctx, rule, srcJarDir, d.Javadoc.srcJars)
-
-	implicitsRsp := android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"implicits.rsp")
-	homeDir := android.PathForModuleOut(ctx, "metalava-home")
-	cmd := metalavaCmd(ctx, rule, javaVersion, d.Javadoc.srcFiles, srcJarList,
-		deps.bootClasspath, deps.classpath, d.Javadoc.sourcepaths, implicitsRsp, homeDir,
-		Bool(d.Javadoc.properties.Sandbox))
-	cmd.Implicits(d.Javadoc.implicits)
-
-	d.stubsFlags(ctx, cmd, stubsDir)
-
-	d.annotationsFlags(ctx, cmd)
-	d.inclusionAnnotationsFlags(ctx, cmd)
-	d.apiLevelsAnnotationsFlags(ctx, cmd)
-
-	if android.InList("--generate-documentation", d.Javadoc.args) {
-		// Currently Metalava have the ability to invoke Javadoc in a seperate process.
-		// Pass "-nodocs" to suppress the Javadoc invocation when Metalava receives
-		// "--generate-documentation" arg. This is not needed when Metalava removes this feature.
-		d.Javadoc.args = append(d.Javadoc.args, "-nodocs")
-	}
-
-	cmd.Flag(strings.Join(d.Javadoc.args, " ")).Implicits(d.Javadoc.argFiles)
-	for _, o := range d.Javadoc.properties.Out {
-		cmd.ImplicitOutput(android.PathForModuleGen(ctx, o))
-	}
-
-	// Add options for the other optional tasks: API-lint and check-released.
-	// We generate separate timestamp files for them.
-
-	doApiLint := false
-	doCheckReleased := false
-
-	// Add API lint options.
-
-	if BoolDefault(d.properties.Check_api.Api_lint.Enabled, false) {
-		doApiLint = true
-
-		newSince := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.New_since)
-		if newSince.Valid() {
-			cmd.FlagWithInput("--api-lint ", newSince.Path())
-		} else {
-			cmd.Flag("--api-lint")
-		}
-		d.apiLintReport = android.PathForModuleOut(ctx, "api_lint_report.txt")
-		cmd.FlagWithOutput("--report-even-if-suppressed ", d.apiLintReport) // TODO:  Change to ":api-lint"
-
-		// TODO(b/154317059): Clean up this whitelist by baselining and/or checking in last-released.
-		if d.Name() != "android.car-system-stubs-docs" &&
-			d.Name() != "android.car-stubs-docs" {
-			cmd.Flag("--lints-as-errors")
-			cmd.Flag("--warnings-as-errors") // Most lints are actually warnings.
-		}
-
-		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.Baseline_file)
-		updatedBaselineOutput := android.PathForModuleOut(ctx, "api_lint_baseline.txt")
-		d.apiLintTimestamp = android.PathForModuleOut(ctx, "api_lint.timestamp")
-
-		// Note this string includes a special shell quote $' ... ', which decodes the "\n"s.
-		// However, because $' ... ' doesn't expand environmental variables, we can't just embed
-		// $PWD, so we have to terminate $'...', use "$PWD", then start $' ... ' again,
-		// which is why we have '"$PWD"$' in it.
-		//
-		// TODO: metalava also has a slightly different message hardcoded. Should we unify this
-		// message and metalava's one?
-		msg := `$'` + // Enclose with $' ... '
-			`************************************************************\n` +
-			`Your API changes are triggering API Lint warnings or errors.\n` +
-			`To make these errors go away, fix the code according to the\n` +
-			`error and/or warning messages above.\n` +
-			`\n` +
-			`If it is not possible to do so, there are workarounds:\n` +
-			`\n` +
-			`1. You can suppress the errors with @SuppressLint("<id>")\n`
-
-		if baselineFile.Valid() {
-			cmd.FlagWithInput("--baseline:api-lint ", baselineFile.Path())
-			cmd.FlagWithOutput("--update-baseline:api-lint ", updatedBaselineOutput)
-
-			msg += fmt.Sprintf(``+
-				`2. You can update the baseline by executing the following\n`+
-				`   command:\n`+
-				`       cp \\\n`+
-				`       "'"$PWD"$'/%s" \\\n`+
-				`       "'"$PWD"$'/%s"\n`+
-				`   To submit the revised baseline.txt to the main Android\n`+
-				`   repository, you will need approval.\n`, updatedBaselineOutput, baselineFile.Path())
-		} else {
-			msg += fmt.Sprintf(``+
-				`2. You can add a baseline file of existing lint failures\n`+
-				`   to the build rule of %s.\n`, d.Name())
-		}
-		// Note the message ends with a ' (single quote), to close the $' ... ' .
-		msg += `************************************************************\n'`
-
-		cmd.FlagWithArg("--error-message:api-lint ", msg)
-	}
-
-	// Add "check released" options. (Detect incompatible API changes from the last public release)
-
-	if apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") {
-		doCheckReleased = true
-
-		if len(d.Javadoc.properties.Out) > 0 {
-			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
-		}
-
-		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Api_file))
-		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Removed_api_file))
-		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Last_released.Baseline_file)
-		updatedBaselineOutput := android.PathForModuleOut(ctx, "last_released_baseline.txt")
-
-		d.checkLastReleasedApiTimestamp = android.PathForModuleOut(ctx, "check_last_released_api.timestamp")
-
-		cmd.FlagWithInput("--check-compatibility:api:released ", apiFile)
-		cmd.FlagWithInput("--check-compatibility:removed:released ", removedApiFile)
-
-		if baselineFile.Valid() {
-			cmd.FlagWithInput("--baseline:compatibility:released ", baselineFile.Path())
-			cmd.FlagWithOutput("--update-baseline:compatibility:released ", updatedBaselineOutput)
-		}
-
-		// Note this string includes quote ($' ... '), which decodes the "\n"s.
-		msg := `$'\n******************************\n` +
-			`You have tried to change the API from what has been previously released in\n` +
-			`an SDK.  Please fix the errors listed above.\n` +
-			`******************************\n'`
-
-		cmd.FlagWithArg("--error-message:compatibility:released ", msg)
-	}
-
-	impRule := android.NewRuleBuilder(pctx, ctx)
-	impCmd := impRule.Command()
-	// An action that copies the ninja generated rsp file to a new location. This allows us to
-	// add a large number of inputs to a file without exceeding bash command length limits (which
-	// would happen if we use the WriteFile rule). The cp is needed because RuleBuilder sets the
-	// rsp file to be ${output}.rsp.
-	impCmd.Text("cp").
-		FlagWithRspFileInputList("", android.PathForModuleOut(ctx, "metalava-implicits.rsp"), cmd.GetImplicits()).
-		Output(implicitsRsp)
-	impRule.Build("implicitsGen", "implicits generation")
-	cmd.Implicit(implicitsRsp)
-
-	if generateStubs {
-		rule.Command().
-			BuiltTool("soong_zip").
-			Flag("-write_if_changed").
-			Flag("-jar").
-			FlagWithOutput("-o ", d.Javadoc.stubsSrcJar).
-			FlagWithArg("-C ", stubsDir.String()).
-			FlagWithArg("-D ", stubsDir.String())
-	}
-
-	if Bool(d.properties.Write_sdk_values) {
-		d.metadataZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"-metadata.zip")
-		rule.Command().
-			BuiltTool("soong_zip").
-			Flag("-write_if_changed").
-			Flag("-d").
-			FlagWithOutput("-o ", d.metadataZip).
-			FlagWithArg("-C ", d.metadataDir.String()).
-			FlagWithArg("-D ", d.metadataDir.String())
-	}
-
-	// TODO: We don't really need two separate API files, but this is a reminiscence of how
-	// we used to run metalava separately for API lint and the "last_released" check. Unify them.
-	if doApiLint {
-		rule.Command().Text("touch").Output(d.apiLintTimestamp)
-	}
-	if doCheckReleased {
-		rule.Command().Text("touch").Output(d.checkLastReleasedApiTimestamp)
-	}
-
-	rule.Restat()
-
-	zipSyncCleanupCmd(rule, srcJarDir)
-
-	rule.Build("metalava", "metalava merged")
-
-	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") {
-
-		if len(d.Javadoc.properties.Out) > 0 {
-			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
-		}
-
-		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Api_file))
-		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Removed_api_file))
-		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Current.Baseline_file)
-
-		if baselineFile.Valid() {
-			ctx.PropertyErrorf("baseline_file", "current API check can't have a baseline file. (module %s)", ctx.ModuleName())
-		}
-
-		d.checkCurrentApiTimestamp = android.PathForModuleOut(ctx, "check_current_api.timestamp")
-
-		rule := android.NewRuleBuilder(pctx, ctx)
-
-		// Diff command line.
-		// -F matches the closest "opening" line, such as "package android {"
-		// and "  public class Intent {".
-		diff := `diff -u -F '{ *$'`
-
-		rule.Command().Text("( true")
-		rule.Command().
-			Text(diff).
-			Input(apiFile).Input(d.apiFile)
-
-		rule.Command().
-			Text(diff).
-			Input(removedApiFile).Input(d.removedApiFile)
-
-		msg := fmt.Sprintf(`\n******************************\n`+
-			`You have tried to change the API from what has been previously approved.\n\n`+
-			`To make these errors go away, you have two choices:\n`+
-			`   1. You can add '@hide' javadoc comments (and remove @SystemApi/@TestApi/etc)\n`+
-			`      to the new methods, etc. shown in the above diff.\n\n`+
-			`   2. You can update current.txt and/or removed.txt by executing the following command:\n`+
-			`         m %s-update-current-api\n\n`+
-			`      To submit the revised current.txt to the main Android repository,\n`+
-			`      you will need approval.\n`+
-			`******************************\n`, ctx.ModuleName())
-
-		rule.Command().
-			Text("touch").Output(d.checkCurrentApiTimestamp).
-			Text(") || (").
-			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
-			Text("; exit 38").
-			Text(")")
-
-		rule.Build("metalavaCurrentApiCheck", "check current API")
-
-		d.updateCurrentApiTimestamp = android.PathForModuleOut(ctx, "update_current_api.timestamp")
-
-		// update API rule
-		rule = android.NewRuleBuilder(pctx, ctx)
-
-		rule.Command().Text("( true")
-
-		rule.Command().
-			Text("cp").Flag("-f").
-			Input(d.apiFile).Flag(apiFile.String())
-
-		rule.Command().
-			Text("cp").Flag("-f").
-			Input(d.removedApiFile).Flag(removedApiFile.String())
-
-		msg = "failed to update public API"
-
-		rule.Command().
-			Text("touch").Output(d.updateCurrentApiTimestamp).
-			Text(") || (").
-			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
-			Text("; exit 38").
-			Text(")")
-
-		rule.Build("metalavaCurrentApiUpdate", "update current API")
-	}
-
-	if String(d.properties.Check_nullability_warnings) != "" {
-		if d.nullabilityWarningsFile == nil {
-			ctx.PropertyErrorf("check_nullability_warnings",
-				"Cannot specify check_nullability_warnings unless validating nullability")
-		}
-
-		checkNullabilityWarnings := android.PathForModuleSrc(ctx, String(d.properties.Check_nullability_warnings))
-
-		d.checkNullabilityWarningsTimestamp = android.PathForModuleOut(ctx, "check_nullability_warnings.timestamp")
-
-		msg := fmt.Sprintf(`\n******************************\n`+
-			`The warnings encountered during nullability annotation validation did\n`+
-			`not match the checked in file of expected warnings. The diffs are shown\n`+
-			`above. You have two options:\n`+
-			`   1. Resolve the differences by editing the nullability annotations.\n`+
-			`   2. Update the file of expected warnings by running:\n`+
-			`         cp %s %s\n`+
-			`       and submitting the updated file as part of your change.`,
-			d.nullabilityWarningsFile, checkNullabilityWarnings)
-
-		rule := android.NewRuleBuilder(pctx, ctx)
-
-		rule.Command().
-			Text("(").
-			Text("diff").Input(checkNullabilityWarnings).Input(d.nullabilityWarningsFile).
-			Text("&&").
-			Text("touch").Output(d.checkNullabilityWarningsTimestamp).
-			Text(") || (").
-			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
-			Text("; exit 38").
-			Text(")")
-
-		rule.Build("nullabilityWarningsCheck", "nullability warnings check")
-	}
-}
-
-//
 // Exported Droiddoc Directory
 //
 var droiddocTemplateTag = dependencyTag{name: "droiddoc-template"}
-var metalavaMergeAnnotationsDirTag = dependencyTag{name: "metalava-merge-annotations-dir"}
-var metalavaMergeInclusionAnnotationsDirTag = dependencyTag{name: "metalava-merge-inclusion-annotations-dir"}
-var metalavaAPILevelsAnnotationsDirTag = dependencyTag{name: "metalava-api-levels-annotations-dir"}
 
 type ExportedDroiddocDirProperties struct {
 	// path to the directory containing Droiddoc related files.
@@ -1662,19 +913,6 @@
 	return module
 }
 
-func StubsDefaultsFactory() android.Module {
-	module := &DocDefaults{}
-
-	module.AddProperties(
-		&JavadocProperties{},
-		&DroidstubsProperties{},
-	)
-
-	android.InitDefaultsModule(module)
-
-	return module
-}
-
 func zipSyncCmd(ctx android.ModuleContext, rule *android.RuleBuilder,
 	srcJarDir android.ModuleOutPath, srcJars android.Paths) android.OutputPath {
 
@@ -1699,94 +937,3 @@
 func zipSyncCleanupCmd(rule *android.RuleBuilder, srcJarDir android.ModuleOutPath) {
 	rule.Command().Text("rm -rf").Text(srcJarDir.String())
 }
-
-var _ android.PrebuiltInterface = (*PrebuiltStubsSources)(nil)
-
-type PrebuiltStubsSourcesProperties struct {
-	Srcs []string `android:"path"`
-}
-
-type PrebuiltStubsSources struct {
-	android.ModuleBase
-	android.DefaultableModuleBase
-	prebuilt android.Prebuilt
-	android.SdkBase
-
-	properties PrebuiltStubsSourcesProperties
-
-	stubsSrcJar android.ModuleOutPath
-}
-
-func (p *PrebuiltStubsSources) OutputFiles(tag string) (android.Paths, error) {
-	switch tag {
-	case "":
-		return android.Paths{p.stubsSrcJar}, nil
-	default:
-		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
-	}
-}
-
-func (d *PrebuiltStubsSources) StubsSrcJar() android.Path {
-	return d.stubsSrcJar
-}
-
-func (p *PrebuiltStubsSources) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	p.stubsSrcJar = android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"stubs.srcjar")
-
-	if len(p.properties.Srcs) != 1 {
-		ctx.PropertyErrorf("srcs", "must only specify one directory path, contains %d paths", len(p.properties.Srcs))
-		return
-	}
-
-	localSrcDir := p.properties.Srcs[0]
-	// Although PathForModuleSrc can return nil if either the path doesn't exist or
-	// the path components are invalid it won't in this case because no components
-	// are specified and the module directory must exist in order to get this far.
-	srcDir := android.PathForModuleSrc(ctx).(android.SourcePath).Join(ctx, localSrcDir)
-
-	// Glob the contents of the directory just in case the directory does not exist.
-	srcGlob := localSrcDir + "/**/*"
-	srcPaths := android.PathsForModuleSrc(ctx, []string{srcGlob})
-
-	rule := android.NewRuleBuilder(pctx, ctx)
-	rule.Command().
-		BuiltTool("soong_zip").
-		Flag("-write_if_changed").
-		Flag("-jar").
-		FlagWithOutput("-o ", p.stubsSrcJar).
-		FlagWithArg("-C ", srcDir.String()).
-		FlagWithRspFileInputList("-r ", p.stubsSrcJar.ReplaceExtension(ctx, "rsp"), srcPaths)
-
-	rule.Restat()
-
-	rule.Build("zip src", "Create srcjar from prebuilt source")
-}
-
-func (p *PrebuiltStubsSources) Prebuilt() *android.Prebuilt {
-	return &p.prebuilt
-}
-
-func (p *PrebuiltStubsSources) Name() string {
-	return p.prebuilt.Name(p.ModuleBase.Name())
-}
-
-// prebuilt_stubs_sources imports a set of java source files as if they were
-// generated by droidstubs.
-//
-// By default, a prebuilt_stubs_sources has a single variant that expects a
-// set of `.java` files generated by droidstubs.
-//
-// Specifying `host_supported: true` will produce two variants, one for use as a dependency of device modules and one
-// for host modules.
-//
-// Intended only for use by sdk snapshots.
-func PrebuiltStubsSourcesFactory() android.Module {
-	module := &PrebuiltStubsSources{}
-
-	module.AddProperties(&module.properties)
-
-	android.InitPrebuiltModule(module, &module.properties.Srcs)
-	android.InitSdkAwareModule(module)
-	InitDroiddocModule(module, android.HostAndDeviceSupported)
-	return module
-}
diff --git a/java/droiddoc_test.go b/java/droiddoc_test.go
new file mode 100644
index 0000000..2b324ae
--- /dev/null
+++ b/java/droiddoc_test.go
@@ -0,0 +1,147 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+
+	"android/soong/android"
+)
+
+func TestDroiddoc(t *testing.T) {
+	ctx, _ := testJavaWithFS(t, `
+		droiddoc_exported_dir {
+		    name: "droiddoc-templates-sdk",
+		    path: ".",
+		}
+		filegroup {
+		    name: "bar-doc-aidl-srcs",
+		    srcs: ["bar-doc/IBar.aidl"],
+		    path: "bar-doc",
+		}
+		droidstubs {
+		    name: "bar-stubs",
+		    srcs: [
+		        "bar-doc/a.java",
+		    ],
+		    exclude_srcs: [
+		        "bar-doc/b.java"
+		    ],
+		    api_levels_annotations_dirs: [
+		      "droiddoc-templates-sdk",
+		    ],
+		    api_levels_annotations_enabled: true,
+		}
+		droiddoc {
+		    name: "bar-doc",
+		    srcs: [
+		        ":bar-stubs",
+		        "bar-doc/IFoo.aidl",
+		        ":bar-doc-aidl-srcs",
+		    ],
+		    custom_template: "droiddoc-templates-sdk",
+		    hdf: [
+		        "android.whichdoc offline",
+		    ],
+		    knowntags: [
+		        "bar-doc/known_oj_tags.txt",
+		    ],
+		    proofread_file: "libcore-proofread.txt",
+		    todo_file: "libcore-docs-todo.html",
+		    flags: ["-offlinemode -title \"libcore\""],
+		}
+		`,
+		map[string][]byte{
+			"bar-doc/a.java": nil,
+			"bar-doc/b.java": nil,
+		})
+	barStubs := ctx.ModuleForTests("bar-stubs", "android_common")
+	barStubsOutputs, err := barStubs.Module().(*Droidstubs).OutputFiles("")
+	if err != nil {
+		t.Errorf("Unexpected error %q retrieving \"bar-stubs\" output file", err)
+	}
+	if len(barStubsOutputs) != 1 {
+		t.Errorf("Expected one output from \"bar-stubs\" got %s", barStubsOutputs)
+	}
+
+	barStubsOutput := barStubsOutputs[0]
+	barDoc := ctx.ModuleForTests("bar-doc", "android_common")
+	javaDoc := barDoc.Rule("javadoc").RelativeToTop()
+	if g, w := android.PathsRelativeToTop(javaDoc.Implicits), android.PathRelativeToTop(barStubsOutput); !inList(w, g) {
+		t.Errorf("implicits of bar-doc must contain %q, but was %q.", w, g)
+	}
+
+	expected := "-sourcepath out/soong/.intermediates/bar-doc/android_common/srcjars "
+	if !strings.Contains(javaDoc.RuleParams.Command, expected) {
+		t.Errorf("bar-doc command does not contain flag %q, but should\n%q", expected, javaDoc.RuleParams.Command)
+	}
+
+	aidl := barDoc.Rule("aidl")
+	if g, w := android.PathsRelativeToTop(javaDoc.Implicits), android.PathRelativeToTop(aidl.Output); !inList(w, g) {
+		t.Errorf("implicits of bar-doc must contain %q, but was %q.", w, g)
+	}
+
+	if g, w := aidl.Implicits.Strings(), []string{"bar-doc/IBar.aidl", "bar-doc/IFoo.aidl"}; !reflect.DeepEqual(w, g) {
+		t.Errorf("aidl inputs must be %q, but was %q", w, g)
+	}
+}
+
+func TestDroiddocArgsAndFlagsCausesError(t *testing.T) {
+	testJavaError(t, "flags is set. Cannot set args", `
+		droiddoc_exported_dir {
+		    name: "droiddoc-templates-sdk",
+		    path: ".",
+		}
+		filegroup {
+		    name: "bar-doc-aidl-srcs",
+		    srcs: ["bar-doc/IBar.aidl"],
+		    path: "bar-doc",
+		}
+		droidstubs {
+		    name: "bar-stubs",
+		    srcs: [
+		        "bar-doc/a.java",
+		    ],
+		    exclude_srcs: [
+		        "bar-doc/b.java"
+		    ],
+		    api_levels_annotations_dirs: [
+		      "droiddoc-templates-sdk",
+		    ],
+		    api_levels_annotations_enabled: true,
+		}
+		droiddoc {
+		    name: "bar-doc",
+		    srcs: [
+		        ":bar-stubs",
+		        "bar-doc/IFoo.aidl",
+		        ":bar-doc-aidl-srcs",
+		    ],
+		    custom_template: "droiddoc-templates-sdk",
+		    hdf: [
+		        "android.whichdoc offline",
+		    ],
+		    knowntags: [
+		        "bar-doc/known_oj_tags.txt",
+		    ],
+		    proofread_file: "libcore-proofread.txt",
+		    todo_file: "libcore-docs-todo.html",
+		    flags: ["-offlinemode -title \"libcore\""],
+		    args: "-offlinemode -title \"libcore\"",
+		}
+		`)
+}
diff --git a/java/droidstubs.go b/java/droidstubs.go
new file mode 100644
index 0000000..4dff98c
--- /dev/null
+++ b/java/droidstubs.go
@@ -0,0 +1,878 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/google/blueprint/proptools"
+
+	"android/soong/android"
+	"android/soong/java/config"
+	"android/soong/remoteexec"
+)
+
+func init() {
+	RegisterStubsBuildComponents(android.InitRegistrationContext)
+}
+
+func RegisterStubsBuildComponents(ctx android.RegistrationContext) {
+	ctx.RegisterModuleType("stubs_defaults", StubsDefaultsFactory)
+
+	ctx.RegisterModuleType("droidstubs", DroidstubsFactory)
+	ctx.RegisterModuleType("droidstubs_host", DroidstubsHostFactory)
+
+	ctx.RegisterModuleType("prebuilt_stubs_sources", PrebuiltStubsSourcesFactory)
+}
+
+//
+// Droidstubs
+//
+type Droidstubs struct {
+	Javadoc
+	android.SdkBase
+
+	properties              DroidstubsProperties
+	apiFile                 android.WritablePath
+	apiXmlFile              android.WritablePath
+	lastReleasedApiXmlFile  android.WritablePath
+	privateApiFile          android.WritablePath
+	removedApiFile          android.WritablePath
+	removedDexApiFile       android.WritablePath
+	nullabilityWarningsFile android.WritablePath
+
+	checkCurrentApiTimestamp      android.WritablePath
+	updateCurrentApiTimestamp     android.WritablePath
+	checkLastReleasedApiTimestamp android.WritablePath
+	apiLintTimestamp              android.WritablePath
+	apiLintReport                 android.WritablePath
+
+	checkNullabilityWarningsTimestamp android.WritablePath
+
+	annotationsZip android.WritablePath
+	apiVersionsXml android.WritablePath
+
+	apiFilePath        android.Path
+	removedApiFilePath android.Path
+
+	metadataZip android.WritablePath
+	metadataDir android.WritablePath
+}
+
+type DroidstubsProperties struct {
+	// The generated public API filename by Metalava, defaults to <module>_api.txt
+	Api_filename *string
+
+	// the generated removed API filename by Metalava, defaults to <module>_removed.txt
+	Removed_api_filename *string
+
+	// the generated removed Dex API filename by Metalava.
+	Removed_dex_api_filename *string
+
+	Check_api struct {
+		Last_released ApiToCheck
+
+		Current ApiToCheck
+
+		Api_lint struct {
+			Enabled *bool
+
+			// If set, performs api_lint on any new APIs not found in the given signature file
+			New_since *string `android:"path"`
+
+			// If not blank, path to the baseline txt file for approved API lint violations.
+			Baseline_file *string `android:"path"`
+		}
+	}
+
+	// user can specify the version of previous released API file in order to do compatibility check.
+	Previous_api *string `android:"path"`
+
+	// is set to true, Metalava will allow framework SDK to contain annotations.
+	Annotations_enabled *bool
+
+	// a list of top-level directories containing files to merge qualifier annotations (i.e. those intended to be included in the stubs written) from.
+	Merge_annotations_dirs []string
+
+	// a list of top-level directories containing Java stub files to merge show/hide annotations from.
+	Merge_inclusion_annotations_dirs []string
+
+	// a file containing a list of classes to do nullability validation for.
+	Validate_nullability_from_list *string
+
+	// a file containing expected warnings produced by validation of nullability annotations.
+	Check_nullability_warnings *string
+
+	// if set to true, allow Metalava to generate doc_stubs source files. Defaults to false.
+	Create_doc_stubs *bool
+
+	// if set to true, cause Metalava to output Javadoc comments in the stubs source files. Defaults to false.
+	// Has no effect if create_doc_stubs: true.
+	Output_javadoc_comments *bool
+
+	// if set to false then do not write out stubs. Defaults to true.
+	//
+	// TODO(b/146727827): Remove capability when we do not need to generate stubs and API separately.
+	Generate_stubs *bool
+
+	// if set to true, provides a hint to the build system that this rule uses a lot of memory,
+	// whicih can be used for scheduling purposes
+	High_mem *bool
+
+	// is set to true, Metalava will allow framework SDK to contain API levels annotations.
+	Api_levels_annotations_enabled *bool
+
+	// the dirs which Metalava extracts API levels annotations from.
+	Api_levels_annotations_dirs []string
+
+	// the filename which Metalava extracts API levels annotations from. Defaults to android.jar.
+	Api_levels_jar_filename *string
+
+	// if set to true, collect the values used by the Dev tools and
+	// write them in files packaged with the SDK. Defaults to false.
+	Write_sdk_values *bool
+}
+
+// droidstubs passes sources files through Metalava to generate stub .java files that only contain the API to be
+// documented, filtering out hidden classes and methods.  The resulting .java files are intended to be passed to
+// a droiddoc module to generate documentation.
+func DroidstubsFactory() android.Module {
+	module := &Droidstubs{}
+
+	module.AddProperties(&module.properties,
+		&module.Javadoc.properties)
+
+	InitDroiddocModule(module, android.HostAndDeviceSupported)
+	android.InitSdkAwareModule(module)
+	return module
+}
+
+// droidstubs_host passes sources files through Metalava to generate stub .java files that only contain the API
+// to be documented, filtering out hidden classes and methods.  The resulting .java files are intended to be
+// passed to a droiddoc_host module to generate documentation.  Use a droidstubs_host instead of a droidstubs
+// module when symbols needed by the source files are provided by java_library_host modules.
+func DroidstubsHostFactory() android.Module {
+	module := &Droidstubs{}
+
+	module.AddProperties(&module.properties,
+		&module.Javadoc.properties)
+
+	InitDroiddocModule(module, android.HostSupported)
+	return module
+}
+
+func (d *Droidstubs) OutputFiles(tag string) (android.Paths, error) {
+	switch tag {
+	case "":
+		return android.Paths{d.stubsSrcJar}, nil
+	case ".docs.zip":
+		return android.Paths{d.docZip}, nil
+	case ".api.txt", android.DefaultDistTag:
+		// This is the default dist path for dist properties that have no tag property.
+		return android.Paths{d.apiFilePath}, nil
+	case ".removed-api.txt":
+		return android.Paths{d.removedApiFilePath}, nil
+	case ".annotations.zip":
+		return android.Paths{d.annotationsZip}, nil
+	case ".api_versions.xml":
+		return android.Paths{d.apiVersionsXml}, nil
+	default:
+		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
+	}
+}
+
+func (d *Droidstubs) ApiFilePath() android.Path {
+	return d.apiFilePath
+}
+
+func (d *Droidstubs) RemovedApiFilePath() android.Path {
+	return d.removedApiFilePath
+}
+
+func (d *Droidstubs) StubsSrcJar() android.Path {
+	return d.stubsSrcJar
+}
+
+var metalavaMergeAnnotationsDirTag = dependencyTag{name: "metalava-merge-annotations-dir"}
+var metalavaMergeInclusionAnnotationsDirTag = dependencyTag{name: "metalava-merge-inclusion-annotations-dir"}
+var metalavaAPILevelsAnnotationsDirTag = dependencyTag{name: "metalava-api-levels-annotations-dir"}
+
+func (d *Droidstubs) DepsMutator(ctx android.BottomUpMutatorContext) {
+	d.Javadoc.addDeps(ctx)
+
+	if len(d.properties.Merge_annotations_dirs) != 0 {
+		for _, mergeAnnotationsDir := range d.properties.Merge_annotations_dirs {
+			ctx.AddDependency(ctx.Module(), metalavaMergeAnnotationsDirTag, mergeAnnotationsDir)
+		}
+	}
+
+	if len(d.properties.Merge_inclusion_annotations_dirs) != 0 {
+		for _, mergeInclusionAnnotationsDir := range d.properties.Merge_inclusion_annotations_dirs {
+			ctx.AddDependency(ctx.Module(), metalavaMergeInclusionAnnotationsDirTag, mergeInclusionAnnotationsDir)
+		}
+	}
+
+	if len(d.properties.Api_levels_annotations_dirs) != 0 {
+		for _, apiLevelsAnnotationsDir := range d.properties.Api_levels_annotations_dirs {
+			ctx.AddDependency(ctx.Module(), metalavaAPILevelsAnnotationsDirTag, apiLevelsAnnotationsDir)
+		}
+	}
+}
+
+func (d *Droidstubs) stubsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand, stubsDir android.OptionalPath) {
+	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
+		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
+		String(d.properties.Api_filename) != "" {
+		filename := proptools.StringDefault(d.properties.Api_filename, ctx.ModuleName()+"_api.txt")
+		d.apiFile = android.PathForModuleOut(ctx, filename)
+		cmd.FlagWithOutput("--api ", d.apiFile)
+		d.apiFilePath = d.apiFile
+	} else if sourceApiFile := proptools.String(d.properties.Check_api.Current.Api_file); sourceApiFile != "" {
+		// If check api is disabled then make the source file available for export.
+		d.apiFilePath = android.PathForModuleSrc(ctx, sourceApiFile)
+	}
+
+	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") ||
+		apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") ||
+		String(d.properties.Removed_api_filename) != "" {
+		filename := proptools.StringDefault(d.properties.Removed_api_filename, ctx.ModuleName()+"_removed.txt")
+		d.removedApiFile = android.PathForModuleOut(ctx, filename)
+		cmd.FlagWithOutput("--removed-api ", d.removedApiFile)
+		d.removedApiFilePath = d.removedApiFile
+	} else if sourceRemovedApiFile := proptools.String(d.properties.Check_api.Current.Removed_api_file); sourceRemovedApiFile != "" {
+		// If check api is disabled then make the source removed api file available for export.
+		d.removedApiFilePath = android.PathForModuleSrc(ctx, sourceRemovedApiFile)
+	}
+
+	if String(d.properties.Removed_dex_api_filename) != "" {
+		d.removedDexApiFile = android.PathForModuleOut(ctx, String(d.properties.Removed_dex_api_filename))
+		cmd.FlagWithOutput("--removed-dex-api ", d.removedDexApiFile)
+	}
+
+	if Bool(d.properties.Write_sdk_values) {
+		d.metadataDir = android.PathForModuleOut(ctx, "metadata")
+		cmd.FlagWithArg("--sdk-values ", d.metadataDir.String())
+	}
+
+	if stubsDir.Valid() {
+		if Bool(d.properties.Create_doc_stubs) {
+			cmd.FlagWithArg("--doc-stubs ", stubsDir.String())
+		} else {
+			cmd.FlagWithArg("--stubs ", stubsDir.String())
+			if !Bool(d.properties.Output_javadoc_comments) {
+				cmd.Flag("--exclude-documentation-from-stubs")
+			}
+		}
+	}
+}
+
+func (d *Droidstubs) annotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
+	if Bool(d.properties.Annotations_enabled) {
+		cmd.Flag("--include-annotations")
+
+		validatingNullability :=
+			android.InList("--validate-nullability-from-merged-stubs", d.Javadoc.args) ||
+				String(d.properties.Validate_nullability_from_list) != ""
+
+		migratingNullability := String(d.properties.Previous_api) != ""
+		if migratingNullability {
+			previousApi := android.PathForModuleSrc(ctx, String(d.properties.Previous_api))
+			cmd.FlagWithInput("--migrate-nullness ", previousApi)
+		}
+
+		if s := String(d.properties.Validate_nullability_from_list); s != "" {
+			cmd.FlagWithInput("--validate-nullability-from-list ", android.PathForModuleSrc(ctx, s))
+		}
+
+		if validatingNullability {
+			d.nullabilityWarningsFile = android.PathForModuleOut(ctx, ctx.ModuleName()+"_nullability_warnings.txt")
+			cmd.FlagWithOutput("--nullability-warnings-txt ", d.nullabilityWarningsFile)
+		}
+
+		d.annotationsZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"_annotations.zip")
+		cmd.FlagWithOutput("--extract-annotations ", d.annotationsZip)
+
+		if len(d.properties.Merge_annotations_dirs) != 0 {
+			d.mergeAnnoDirFlags(ctx, cmd)
+		}
+
+		// TODO(tnorbye): find owners to fix these warnings when annotation was enabled.
+		cmd.FlagWithArg("--hide ", "HiddenTypedefConstant").
+			FlagWithArg("--hide ", "SuperfluousPrefix").
+			FlagWithArg("--hide ", "AnnotationExtraction")
+	}
+}
+
+func (d *Droidstubs) mergeAnnoDirFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
+	ctx.VisitDirectDepsWithTag(metalavaMergeAnnotationsDirTag, func(m android.Module) {
+		if t, ok := m.(*ExportedDroiddocDir); ok {
+			cmd.FlagWithArg("--merge-qualifier-annotations ", t.dir.String()).Implicits(t.deps)
+		} else {
+			ctx.PropertyErrorf("merge_annotations_dirs",
+				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
+		}
+	})
+}
+
+func (d *Droidstubs) inclusionAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
+	ctx.VisitDirectDepsWithTag(metalavaMergeInclusionAnnotationsDirTag, func(m android.Module) {
+		if t, ok := m.(*ExportedDroiddocDir); ok {
+			cmd.FlagWithArg("--merge-inclusion-annotations ", t.dir.String()).Implicits(t.deps)
+		} else {
+			ctx.PropertyErrorf("merge_inclusion_annotations_dirs",
+				"module %q is not a metalava merge-annotations dir", ctx.OtherModuleName(m))
+		}
+	})
+}
+
+func (d *Droidstubs) apiLevelsAnnotationsFlags(ctx android.ModuleContext, cmd *android.RuleBuilderCommand) {
+	if !Bool(d.properties.Api_levels_annotations_enabled) {
+		return
+	}
+
+	d.apiVersionsXml = android.PathForModuleOut(ctx, "api-versions.xml")
+
+	if len(d.properties.Api_levels_annotations_dirs) == 0 {
+		ctx.PropertyErrorf("api_levels_annotations_dirs",
+			"has to be non-empty if api levels annotations was enabled!")
+	}
+
+	cmd.FlagWithOutput("--generate-api-levels ", d.apiVersionsXml)
+	cmd.FlagWithInput("--apply-api-levels ", d.apiVersionsXml)
+	cmd.FlagWithArg("--current-version ", ctx.Config().PlatformSdkVersion().String())
+	cmd.FlagWithArg("--current-codename ", ctx.Config().PlatformSdkCodename())
+
+	filename := proptools.StringDefault(d.properties.Api_levels_jar_filename, "android.jar")
+
+	ctx.VisitDirectDepsWithTag(metalavaAPILevelsAnnotationsDirTag, func(m android.Module) {
+		if t, ok := m.(*ExportedDroiddocDir); ok {
+			for _, dep := range t.deps {
+				if strings.HasSuffix(dep.String(), filename) {
+					cmd.Implicit(dep)
+				}
+			}
+			cmd.FlagWithArg("--android-jar-pattern ", t.dir.String()+"/%/public/"+filename)
+		} else {
+			ctx.PropertyErrorf("api_levels_annotations_dirs",
+				"module %q is not a metalava api-levels-annotations dir", ctx.OtherModuleName(m))
+		}
+	})
+}
+
+func metalavaCmd(ctx android.ModuleContext, rule *android.RuleBuilder, javaVersion javaVersion, srcs android.Paths,
+	srcJarList android.Path, bootclasspath, classpath classpath, sourcepaths android.Paths,
+	implicitsRsp, homeDir android.WritablePath, sandbox bool) *android.RuleBuilderCommand {
+	rule.Command().Text("rm -rf").Flag(homeDir.String())
+	rule.Command().Text("mkdir -p").Flag(homeDir.String())
+
+	cmd := rule.Command()
+	cmd.FlagWithArg("ANDROID_PREFS_ROOT=", homeDir.String())
+
+	if ctx.Config().UseRBE() && ctx.Config().IsEnvTrue("RBE_METALAVA") {
+		rule.Remoteable(android.RemoteRuleSupports{RBE: true})
+		pool := ctx.Config().GetenvWithDefault("RBE_METALAVA_POOL", "metalava")
+		execStrategy := ctx.Config().GetenvWithDefault("RBE_METALAVA_EXEC_STRATEGY", remoteexec.LocalExecStrategy)
+		labels := map[string]string{"type": "compile", "lang": "java", "compiler": "metalava"}
+		if !sandbox {
+			execStrategy = remoteexec.LocalExecStrategy
+			labels["shallow"] = "true"
+		}
+		inputs := []string{
+			ctx.Config().HostJavaToolPath(ctx, "metalava").String(),
+			homeDir.String(),
+		}
+		if v := ctx.Config().Getenv("RBE_METALAVA_INPUTS"); v != "" {
+			inputs = append(inputs, strings.Split(v, ",")...)
+		}
+		cmd.Text((&remoteexec.REParams{
+			Labels:               labels,
+			ExecStrategy:         execStrategy,
+			Inputs:               inputs,
+			RSPFiles:             []string{implicitsRsp.String()},
+			ToolchainInputs:      []string{config.JavaCmd(ctx).String()},
+			Platform:             map[string]string{remoteexec.PoolKey: pool},
+			EnvironmentVariables: []string{"ANDROID_PREFS_ROOT"},
+		}).NoVarTemplate(ctx.Config().RBEWrapper()))
+	}
+
+	cmd.BuiltTool("metalava").
+		Flag(config.JavacVmFlags).
+		Flag("-J--add-opens=java.base/java.util=ALL-UNNAMED").
+		FlagWithArg("-encoding ", "UTF-8").
+		FlagWithArg("-source ", javaVersion.String()).
+		FlagWithRspFileInputList("@", android.PathForModuleOut(ctx, "metalava.rsp"), srcs).
+		FlagWithInput("@", srcJarList)
+
+	if javaHome := ctx.Config().Getenv("ANDROID_JAVA_HOME"); javaHome != "" {
+		cmd.Implicit(android.PathForSource(ctx, javaHome))
+	}
+
+	if sandbox {
+		cmd.FlagWithOutput("--strict-input-files ", android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"violations.txt"))
+	} else {
+		cmd.FlagWithOutput("--strict-input-files:warn ", android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"violations.txt"))
+	}
+
+	if implicitsRsp != nil {
+		cmd.FlagWithArg("--strict-input-files-exempt ", "@"+implicitsRsp.String())
+	}
+
+	if len(bootclasspath) > 0 {
+		cmd.FlagWithInputList("-bootclasspath ", bootclasspath.Paths(), ":")
+	}
+
+	if len(classpath) > 0 {
+		cmd.FlagWithInputList("-classpath ", classpath.Paths(), ":")
+	}
+
+	if len(sourcepaths) > 0 {
+		cmd.FlagWithList("-sourcepath ", sourcepaths.Strings(), ":")
+	} else {
+		cmd.FlagWithArg("-sourcepath ", `""`)
+	}
+
+	cmd.Flag("--no-banner").
+		Flag("--color").
+		Flag("--quiet").
+		Flag("--format=v2").
+		FlagWithArg("--repeat-errors-max ", "10").
+		FlagWithArg("--hide ", "UnresolvedImport")
+
+	return cmd
+}
+
+func (d *Droidstubs) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	deps := d.Javadoc.collectDeps(ctx)
+
+	javaVersion := getJavaVersion(ctx, String(d.Javadoc.properties.Java_version), sdkContext(d))
+
+	// Create rule for metalava
+
+	srcJarDir := android.PathForModuleOut(ctx, "srcjars")
+
+	rule := android.NewRuleBuilder(pctx, ctx)
+
+	if BoolDefault(d.properties.High_mem, false) {
+		// This metalava run uses lots of memory, restrict the number of metalava jobs that can run in parallel.
+		rule.HighMem()
+	}
+
+	generateStubs := BoolDefault(d.properties.Generate_stubs, true)
+	var stubsDir android.OptionalPath
+	if generateStubs {
+		d.Javadoc.stubsSrcJar = android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"stubs.srcjar")
+		stubsDir = android.OptionalPathForPath(android.PathForModuleOut(ctx, "stubsDir"))
+		rule.Command().Text("rm -rf").Text(stubsDir.String())
+		rule.Command().Text("mkdir -p").Text(stubsDir.String())
+	}
+
+	srcJarList := zipSyncCmd(ctx, rule, srcJarDir, d.Javadoc.srcJars)
+
+	implicitsRsp := android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"implicits.rsp")
+	homeDir := android.PathForModuleOut(ctx, "metalava-home")
+	cmd := metalavaCmd(ctx, rule, javaVersion, d.Javadoc.srcFiles, srcJarList,
+		deps.bootClasspath, deps.classpath, d.Javadoc.sourcepaths, implicitsRsp, homeDir,
+		Bool(d.Javadoc.properties.Sandbox))
+	cmd.Implicits(d.Javadoc.implicits)
+
+	d.stubsFlags(ctx, cmd, stubsDir)
+
+	d.annotationsFlags(ctx, cmd)
+	d.inclusionAnnotationsFlags(ctx, cmd)
+	d.apiLevelsAnnotationsFlags(ctx, cmd)
+
+	if android.InList("--generate-documentation", d.Javadoc.args) {
+		// Currently Metalava have the ability to invoke Javadoc in a seperate process.
+		// Pass "-nodocs" to suppress the Javadoc invocation when Metalava receives
+		// "--generate-documentation" arg. This is not needed when Metalava removes this feature.
+		d.Javadoc.args = append(d.Javadoc.args, "-nodocs")
+	}
+
+	cmd.Flag(strings.Join(d.Javadoc.args, " ")).Implicits(d.Javadoc.argFiles)
+	for _, o := range d.Javadoc.properties.Out {
+		cmd.ImplicitOutput(android.PathForModuleGen(ctx, o))
+	}
+
+	// Add options for the other optional tasks: API-lint and check-released.
+	// We generate separate timestamp files for them.
+
+	doApiLint := false
+	doCheckReleased := false
+
+	// Add API lint options.
+
+	if BoolDefault(d.properties.Check_api.Api_lint.Enabled, false) {
+		doApiLint = true
+
+		newSince := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.New_since)
+		if newSince.Valid() {
+			cmd.FlagWithInput("--api-lint ", newSince.Path())
+		} else {
+			cmd.Flag("--api-lint")
+		}
+		d.apiLintReport = android.PathForModuleOut(ctx, "api_lint_report.txt")
+		cmd.FlagWithOutput("--report-even-if-suppressed ", d.apiLintReport) // TODO:  Change to ":api-lint"
+
+		// TODO(b/154317059): Clean up this whitelist by baselining and/or checking in last-released.
+		if d.Name() != "android.car-system-stubs-docs" &&
+			d.Name() != "android.car-stubs-docs" {
+			cmd.Flag("--lints-as-errors")
+			cmd.Flag("--warnings-as-errors") // Most lints are actually warnings.
+		}
+
+		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Api_lint.Baseline_file)
+		updatedBaselineOutput := android.PathForModuleOut(ctx, "api_lint_baseline.txt")
+		d.apiLintTimestamp = android.PathForModuleOut(ctx, "api_lint.timestamp")
+
+		// Note this string includes a special shell quote $' ... ', which decodes the "\n"s.
+		// However, because $' ... ' doesn't expand environmental variables, we can't just embed
+		// $PWD, so we have to terminate $'...', use "$PWD", then start $' ... ' again,
+		// which is why we have '"$PWD"$' in it.
+		//
+		// TODO: metalava also has a slightly different message hardcoded. Should we unify this
+		// message and metalava's one?
+		msg := `$'` + // Enclose with $' ... '
+			`************************************************************\n` +
+			`Your API changes are triggering API Lint warnings or errors.\n` +
+			`To make these errors go away, fix the code according to the\n` +
+			`error and/or warning messages above.\n` +
+			`\n` +
+			`If it is not possible to do so, there are workarounds:\n` +
+			`\n` +
+			`1. You can suppress the errors with @SuppressLint("<id>")\n`
+
+		if baselineFile.Valid() {
+			cmd.FlagWithInput("--baseline:api-lint ", baselineFile.Path())
+			cmd.FlagWithOutput("--update-baseline:api-lint ", updatedBaselineOutput)
+
+			msg += fmt.Sprintf(``+
+				`2. You can update the baseline by executing the following\n`+
+				`   command:\n`+
+				`       cp \\\n`+
+				`       "'"$PWD"$'/%s" \\\n`+
+				`       "'"$PWD"$'/%s"\n`+
+				`   To submit the revised baseline.txt to the main Android\n`+
+				`   repository, you will need approval.\n`, updatedBaselineOutput, baselineFile.Path())
+		} else {
+			msg += fmt.Sprintf(``+
+				`2. You can add a baseline file of existing lint failures\n`+
+				`   to the build rule of %s.\n`, d.Name())
+		}
+		// Note the message ends with a ' (single quote), to close the $' ... ' .
+		msg += `************************************************************\n'`
+
+		cmd.FlagWithArg("--error-message:api-lint ", msg)
+	}
+
+	// Add "check released" options. (Detect incompatible API changes from the last public release)
+
+	if apiCheckEnabled(ctx, d.properties.Check_api.Last_released, "last_released") {
+		doCheckReleased = true
+
+		if len(d.Javadoc.properties.Out) > 0 {
+			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
+		}
+
+		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Api_file))
+		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Last_released.Removed_api_file))
+		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Last_released.Baseline_file)
+		updatedBaselineOutput := android.PathForModuleOut(ctx, "last_released_baseline.txt")
+
+		d.checkLastReleasedApiTimestamp = android.PathForModuleOut(ctx, "check_last_released_api.timestamp")
+
+		cmd.FlagWithInput("--check-compatibility:api:released ", apiFile)
+		cmd.FlagWithInput("--check-compatibility:removed:released ", removedApiFile)
+
+		if baselineFile.Valid() {
+			cmd.FlagWithInput("--baseline:compatibility:released ", baselineFile.Path())
+			cmd.FlagWithOutput("--update-baseline:compatibility:released ", updatedBaselineOutput)
+		}
+
+		// Note this string includes quote ($' ... '), which decodes the "\n"s.
+		msg := `$'\n******************************\n` +
+			`You have tried to change the API from what has been previously released in\n` +
+			`an SDK.  Please fix the errors listed above.\n` +
+			`******************************\n'`
+
+		cmd.FlagWithArg("--error-message:compatibility:released ", msg)
+	}
+
+	impRule := android.NewRuleBuilder(pctx, ctx)
+	impCmd := impRule.Command()
+	// An action that copies the ninja generated rsp file to a new location. This allows us to
+	// add a large number of inputs to a file without exceeding bash command length limits (which
+	// would happen if we use the WriteFile rule). The cp is needed because RuleBuilder sets the
+	// rsp file to be ${output}.rsp.
+	impCmd.Text("cp").
+		FlagWithRspFileInputList("", android.PathForModuleOut(ctx, "metalava-implicits.rsp"), cmd.GetImplicits()).
+		Output(implicitsRsp)
+	impRule.Build("implicitsGen", "implicits generation")
+	cmd.Implicit(implicitsRsp)
+
+	if generateStubs {
+		rule.Command().
+			BuiltTool("soong_zip").
+			Flag("-write_if_changed").
+			Flag("-jar").
+			FlagWithOutput("-o ", d.Javadoc.stubsSrcJar).
+			FlagWithArg("-C ", stubsDir.String()).
+			FlagWithArg("-D ", stubsDir.String())
+	}
+
+	if Bool(d.properties.Write_sdk_values) {
+		d.metadataZip = android.PathForModuleOut(ctx, ctx.ModuleName()+"-metadata.zip")
+		rule.Command().
+			BuiltTool("soong_zip").
+			Flag("-write_if_changed").
+			Flag("-d").
+			FlagWithOutput("-o ", d.metadataZip).
+			FlagWithArg("-C ", d.metadataDir.String()).
+			FlagWithArg("-D ", d.metadataDir.String())
+	}
+
+	// TODO: We don't really need two separate API files, but this is a reminiscence of how
+	// we used to run metalava separately for API lint and the "last_released" check. Unify them.
+	if doApiLint {
+		rule.Command().Text("touch").Output(d.apiLintTimestamp)
+	}
+	if doCheckReleased {
+		rule.Command().Text("touch").Output(d.checkLastReleasedApiTimestamp)
+	}
+
+	rule.Restat()
+
+	zipSyncCleanupCmd(rule, srcJarDir)
+
+	rule.Build("metalava", "metalava merged")
+
+	if apiCheckEnabled(ctx, d.properties.Check_api.Current, "current") {
+
+		if len(d.Javadoc.properties.Out) > 0 {
+			ctx.PropertyErrorf("out", "out property may not be combined with check_api")
+		}
+
+		apiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Api_file))
+		removedApiFile := android.PathForModuleSrc(ctx, String(d.properties.Check_api.Current.Removed_api_file))
+		baselineFile := android.OptionalPathForModuleSrc(ctx, d.properties.Check_api.Current.Baseline_file)
+
+		if baselineFile.Valid() {
+			ctx.PropertyErrorf("baseline_file", "current API check can't have a baseline file. (module %s)", ctx.ModuleName())
+		}
+
+		d.checkCurrentApiTimestamp = android.PathForModuleOut(ctx, "check_current_api.timestamp")
+
+		rule := android.NewRuleBuilder(pctx, ctx)
+
+		// Diff command line.
+		// -F matches the closest "opening" line, such as "package android {"
+		// and "  public class Intent {".
+		diff := `diff -u -F '{ *$'`
+
+		rule.Command().Text("( true")
+		rule.Command().
+			Text(diff).
+			Input(apiFile).Input(d.apiFile)
+
+		rule.Command().
+			Text(diff).
+			Input(removedApiFile).Input(d.removedApiFile)
+
+		msg := fmt.Sprintf(`\n******************************\n`+
+			`You have tried to change the API from what has been previously approved.\n\n`+
+			`To make these errors go away, you have two choices:\n`+
+			`   1. You can add '@hide' javadoc comments (and remove @SystemApi/@TestApi/etc)\n`+
+			`      to the new methods, etc. shown in the above diff.\n\n`+
+			`   2. You can update current.txt and/or removed.txt by executing the following command:\n`+
+			`         m %s-update-current-api\n\n`+
+			`      To submit the revised current.txt to the main Android repository,\n`+
+			`      you will need approval.\n`+
+			`******************************\n`, ctx.ModuleName())
+
+		rule.Command().
+			Text("touch").Output(d.checkCurrentApiTimestamp).
+			Text(") || (").
+			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
+			Text("; exit 38").
+			Text(")")
+
+		rule.Build("metalavaCurrentApiCheck", "check current API")
+
+		d.updateCurrentApiTimestamp = android.PathForModuleOut(ctx, "update_current_api.timestamp")
+
+		// update API rule
+		rule = android.NewRuleBuilder(pctx, ctx)
+
+		rule.Command().Text("( true")
+
+		rule.Command().
+			Text("cp").Flag("-f").
+			Input(d.apiFile).Flag(apiFile.String())
+
+		rule.Command().
+			Text("cp").Flag("-f").
+			Input(d.removedApiFile).Flag(removedApiFile.String())
+
+		msg = "failed to update public API"
+
+		rule.Command().
+			Text("touch").Output(d.updateCurrentApiTimestamp).
+			Text(") || (").
+			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
+			Text("; exit 38").
+			Text(")")
+
+		rule.Build("metalavaCurrentApiUpdate", "update current API")
+	}
+
+	if String(d.properties.Check_nullability_warnings) != "" {
+		if d.nullabilityWarningsFile == nil {
+			ctx.PropertyErrorf("check_nullability_warnings",
+				"Cannot specify check_nullability_warnings unless validating nullability")
+		}
+
+		checkNullabilityWarnings := android.PathForModuleSrc(ctx, String(d.properties.Check_nullability_warnings))
+
+		d.checkNullabilityWarningsTimestamp = android.PathForModuleOut(ctx, "check_nullability_warnings.timestamp")
+
+		msg := fmt.Sprintf(`\n******************************\n`+
+			`The warnings encountered during nullability annotation validation did\n`+
+			`not match the checked in file of expected warnings. The diffs are shown\n`+
+			`above. You have two options:\n`+
+			`   1. Resolve the differences by editing the nullability annotations.\n`+
+			`   2. Update the file of expected warnings by running:\n`+
+			`         cp %s %s\n`+
+			`       and submitting the updated file as part of your change.`,
+			d.nullabilityWarningsFile, checkNullabilityWarnings)
+
+		rule := android.NewRuleBuilder(pctx, ctx)
+
+		rule.Command().
+			Text("(").
+			Text("diff").Input(checkNullabilityWarnings).Input(d.nullabilityWarningsFile).
+			Text("&&").
+			Text("touch").Output(d.checkNullabilityWarningsTimestamp).
+			Text(") || (").
+			Text("echo").Flag("-e").Flag(`"` + msg + `"`).
+			Text("; exit 38").
+			Text(")")
+
+		rule.Build("nullabilityWarningsCheck", "nullability warnings check")
+	}
+}
+
+func StubsDefaultsFactory() android.Module {
+	module := &DocDefaults{}
+
+	module.AddProperties(
+		&JavadocProperties{},
+		&DroidstubsProperties{},
+	)
+
+	android.InitDefaultsModule(module)
+
+	return module
+}
+
+var _ android.PrebuiltInterface = (*PrebuiltStubsSources)(nil)
+
+type PrebuiltStubsSourcesProperties struct {
+	Srcs []string `android:"path"`
+}
+
+type PrebuiltStubsSources struct {
+	android.ModuleBase
+	android.DefaultableModuleBase
+	prebuilt android.Prebuilt
+	android.SdkBase
+
+	properties PrebuiltStubsSourcesProperties
+
+	stubsSrcJar android.ModuleOutPath
+}
+
+func (p *PrebuiltStubsSources) OutputFiles(tag string) (android.Paths, error) {
+	switch tag {
+	case "":
+		return android.Paths{p.stubsSrcJar}, nil
+	default:
+		return nil, fmt.Errorf("unsupported module reference tag %q", tag)
+	}
+}
+
+func (d *PrebuiltStubsSources) StubsSrcJar() android.Path {
+	return d.stubsSrcJar
+}
+
+func (p *PrebuiltStubsSources) GenerateAndroidBuildActions(ctx android.ModuleContext) {
+	p.stubsSrcJar = android.PathForModuleOut(ctx, ctx.ModuleName()+"-"+"stubs.srcjar")
+
+	if len(p.properties.Srcs) != 1 {
+		ctx.PropertyErrorf("srcs", "must only specify one directory path, contains %d paths", len(p.properties.Srcs))
+		return
+	}
+
+	localSrcDir := p.properties.Srcs[0]
+	// Although PathForModuleSrc can return nil if either the path doesn't exist or
+	// the path components are invalid it won't in this case because no components
+	// are specified and the module directory must exist in order to get this far.
+	srcDir := android.PathForModuleSrc(ctx).(android.SourcePath).Join(ctx, localSrcDir)
+
+	// Glob the contents of the directory just in case the directory does not exist.
+	srcGlob := localSrcDir + "/**/*"
+	srcPaths := android.PathsForModuleSrc(ctx, []string{srcGlob})
+
+	rule := android.NewRuleBuilder(pctx, ctx)
+	rule.Command().
+		BuiltTool("soong_zip").
+		Flag("-write_if_changed").
+		Flag("-jar").
+		FlagWithOutput("-o ", p.stubsSrcJar).
+		FlagWithArg("-C ", srcDir.String()).
+		FlagWithRspFileInputList("-r ", p.stubsSrcJar.ReplaceExtension(ctx, "rsp"), srcPaths)
+
+	rule.Restat()
+
+	rule.Build("zip src", "Create srcjar from prebuilt source")
+}
+
+func (p *PrebuiltStubsSources) Prebuilt() *android.Prebuilt {
+	return &p.prebuilt
+}
+
+func (p *PrebuiltStubsSources) Name() string {
+	return p.prebuilt.Name(p.ModuleBase.Name())
+}
+
+// prebuilt_stubs_sources imports a set of java source files as if they were
+// generated by droidstubs.
+//
+// By default, a prebuilt_stubs_sources has a single variant that expects a
+// set of `.java` files generated by droidstubs.
+//
+// Specifying `host_supported: true` will produce two variants, one for use as a dependency of device modules and one
+// for host modules.
+//
+// Intended only for use by sdk snapshots.
+func PrebuiltStubsSourcesFactory() android.Module {
+	module := &PrebuiltStubsSources{}
+
+	module.AddProperties(&module.properties)
+
+	android.InitPrebuiltModule(module, &module.properties.Srcs)
+	android.InitSdkAwareModule(module)
+	InitDroiddocModule(module, android.HostAndDeviceSupported)
+	return module
+}
diff --git a/java/droidstubs_test.go b/java/droidstubs_test.go
new file mode 100644
index 0000000..d450c1a
--- /dev/null
+++ b/java/droidstubs_test.go
@@ -0,0 +1,138 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package java
+
+import (
+	"strings"
+	"testing"
+
+	"android/soong/android"
+)
+
+func TestDroidstubs(t *testing.T) {
+	ctx, _ := testJavaWithFS(t, `
+		droiddoc_exported_dir {
+			name: "droiddoc-templates-sdk",
+			path: ".",
+		}
+
+		droidstubs {
+			name: "bar-stubs",
+			srcs: ["bar-doc/a.java"],
+			api_levels_annotations_dirs: ["droiddoc-templates-sdk"],
+			api_levels_annotations_enabled: true,
+		}
+
+		droidstubs {
+			name: "bar-stubs-other",
+			srcs: ["bar-doc/a.java"],
+			high_mem: true,
+			api_levels_annotations_dirs: ["droiddoc-templates-sdk"],
+			api_levels_annotations_enabled: true,
+			api_levels_jar_filename: "android.other.jar",
+		}
+		`,
+		map[string][]byte{
+			"bar-doc/a.java": nil,
+		})
+	testcases := []struct {
+		moduleName          string
+		expectedJarFilename string
+		high_mem            bool
+	}{
+		{
+			moduleName:          "bar-stubs",
+			expectedJarFilename: "android.jar",
+			high_mem:            false,
+		},
+		{
+			moduleName:          "bar-stubs-other",
+			expectedJarFilename: "android.other.jar",
+			high_mem:            true,
+		},
+	}
+	for _, c := range testcases {
+		m := ctx.ModuleForTests(c.moduleName, "android_common")
+		metalava := m.Rule("metalava")
+		rp := metalava.RuleParams
+		expected := "--android-jar-pattern ./%/public/" + c.expectedJarFilename
+		if actual := rp.Command; !strings.Contains(actual, expected) {
+			t.Errorf("For %q, expected metalava argument %q, but was not found %q", c.moduleName, expected, actual)
+		}
+
+		if actual := rp.Pool != nil && strings.Contains(rp.Pool.String(), "highmem"); actual != c.high_mem {
+			t.Errorf("Expected %q high_mem to be %v, was %v", c.moduleName, c.high_mem, actual)
+		}
+	}
+}
+
+func TestDroidstubsWithSystemModules(t *testing.T) {
+	ctx, _ := testJava(t, `
+		droidstubs {
+		    name: "stubs-source-system-modules",
+		    srcs: [
+		        "bar-doc/a.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "source-system-modules",
+		}
+
+		java_library {
+				name: "source-jar",
+		    srcs: [
+		        "a.java",
+		    ],
+		}
+
+		java_system_modules {
+				name: "source-system-modules",
+				libs: ["source-jar"],
+		}
+
+		droidstubs {
+		    name: "stubs-prebuilt-system-modules",
+		    srcs: [
+		        "bar-doc/a.java",
+		    ],
+				sdk_version: "none",
+				system_modules: "prebuilt-system-modules",
+		}
+
+		java_import {
+				name: "prebuilt-jar",
+				jars: ["a.jar"],
+		}
+
+		java_system_modules_import {
+				name: "prebuilt-system-modules",
+				libs: ["prebuilt-jar"],
+		}
+		`)
+
+	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-source-system-modules", "source-jar.jar")
+
+	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-prebuilt-system-modules", "prebuilt-jar.jar")
+}
+
+func checkSystemModulesUseByDroidstubs(t *testing.T, ctx *android.TestContext, moduleName string, systemJar string) {
+	metalavaRule := ctx.ModuleForTests(moduleName, "android_common").Rule("metalava")
+	var systemJars []string
+	for _, i := range metalavaRule.Implicits {
+		systemJars = append(systemJars, i.Base())
+	}
+	if len(systemJars) < 1 || systemJars[0] != systemJar {
+		t.Errorf("inputs of %q must be []string{%q}, but was %#v.", moduleName, systemJar, systemJars)
+	}
+}
diff --git a/java/java_test.go b/java/java_test.go
index 5a13044..2ade0fe 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -1370,246 +1370,6 @@
 	}
 }
 
-func TestDroiddoc(t *testing.T) {
-	ctx, _ := testJavaWithFS(t, `
-		droiddoc_exported_dir {
-		    name: "droiddoc-templates-sdk",
-		    path: ".",
-		}
-		filegroup {
-		    name: "bar-doc-aidl-srcs",
-		    srcs: ["bar-doc/IBar.aidl"],
-		    path: "bar-doc",
-		}
-		droidstubs {
-		    name: "bar-stubs",
-		    srcs: [
-		        "bar-doc/a.java",
-		    ],
-		    exclude_srcs: [
-		        "bar-doc/b.java"
-		    ],
-		    api_levels_annotations_dirs: [
-		      "droiddoc-templates-sdk",
-		    ],
-		    api_levels_annotations_enabled: true,
-		}
-		droiddoc {
-		    name: "bar-doc",
-		    srcs: [
-		        ":bar-stubs",
-		        "bar-doc/IFoo.aidl",
-		        ":bar-doc-aidl-srcs",
-		    ],
-		    custom_template: "droiddoc-templates-sdk",
-		    hdf: [
-		        "android.whichdoc offline",
-		    ],
-		    knowntags: [
-		        "bar-doc/known_oj_tags.txt",
-		    ],
-		    proofread_file: "libcore-proofread.txt",
-		    todo_file: "libcore-docs-todo.html",
-		    flags: ["-offlinemode -title \"libcore\""],
-		}
-		`,
-		map[string][]byte{
-			"bar-doc/a.java": nil,
-			"bar-doc/b.java": nil,
-		})
-	barStubs := ctx.ModuleForTests("bar-stubs", "android_common")
-	barStubsOutputs, err := barStubs.Module().(*Droidstubs).OutputFiles("")
-	if err != nil {
-		t.Errorf("Unexpected error %q retrieving \"bar-stubs\" output file", err)
-	}
-	if len(barStubsOutputs) != 1 {
-		t.Errorf("Expected one output from \"bar-stubs\" got %s", barStubsOutputs)
-	}
-
-	barStubsOutput := barStubsOutputs[0]
-	barDoc := ctx.ModuleForTests("bar-doc", "android_common")
-	javaDoc := barDoc.Rule("javadoc").RelativeToTop()
-	if g, w := android.PathsRelativeToTop(javaDoc.Implicits), android.PathRelativeToTop(barStubsOutput); !inList(w, g) {
-		t.Errorf("implicits of bar-doc must contain %q, but was %q.", w, g)
-	}
-
-	expected := "-sourcepath out/soong/.intermediates/bar-doc/android_common/srcjars "
-	if !strings.Contains(javaDoc.RuleParams.Command, expected) {
-		t.Errorf("bar-doc command does not contain flag %q, but should\n%q", expected, javaDoc.RuleParams.Command)
-	}
-
-	aidl := barDoc.Rule("aidl")
-	if g, w := android.PathsRelativeToTop(javaDoc.Implicits), android.PathRelativeToTop(aidl.Output); !inList(w, g) {
-		t.Errorf("implicits of bar-doc must contain %q, but was %q.", w, g)
-	}
-
-	if g, w := aidl.Implicits.Strings(), []string{"bar-doc/IBar.aidl", "bar-doc/IFoo.aidl"}; !reflect.DeepEqual(w, g) {
-		t.Errorf("aidl inputs must be %q, but was %q", w, g)
-	}
-}
-
-func TestDroiddocArgsAndFlagsCausesError(t *testing.T) {
-	testJavaError(t, "flags is set. Cannot set args", `
-		droiddoc_exported_dir {
-		    name: "droiddoc-templates-sdk",
-		    path: ".",
-		}
-		filegroup {
-		    name: "bar-doc-aidl-srcs",
-		    srcs: ["bar-doc/IBar.aidl"],
-		    path: "bar-doc",
-		}
-		droidstubs {
-		    name: "bar-stubs",
-		    srcs: [
-		        "bar-doc/a.java",
-		    ],
-		    exclude_srcs: [
-		        "bar-doc/b.java"
-		    ],
-		    api_levels_annotations_dirs: [
-		      "droiddoc-templates-sdk",
-		    ],
-		    api_levels_annotations_enabled: true,
-		}
-		droiddoc {
-		    name: "bar-doc",
-		    srcs: [
-		        ":bar-stubs",
-		        "bar-doc/IFoo.aidl",
-		        ":bar-doc-aidl-srcs",
-		    ],
-		    custom_template: "droiddoc-templates-sdk",
-		    hdf: [
-		        "android.whichdoc offline",
-		    ],
-		    knowntags: [
-		        "bar-doc/known_oj_tags.txt",
-		    ],
-		    proofread_file: "libcore-proofread.txt",
-		    todo_file: "libcore-docs-todo.html",
-		    flags: ["-offlinemode -title \"libcore\""],
-		    args: "-offlinemode -title \"libcore\"",
-		}
-		`)
-}
-
-func TestDroidstubs(t *testing.T) {
-	ctx, _ := testJavaWithFS(t, `
-		droiddoc_exported_dir {
-			name: "droiddoc-templates-sdk",
-			path: ".",
-		}
-
-		droidstubs {
-			name: "bar-stubs",
-			srcs: ["bar-doc/a.java"],
-			api_levels_annotations_dirs: ["droiddoc-templates-sdk"],
-			api_levels_annotations_enabled: true,
-		}
-
-		droidstubs {
-			name: "bar-stubs-other",
-			srcs: ["bar-doc/a.java"],
-			high_mem: true,
-			api_levels_annotations_dirs: ["droiddoc-templates-sdk"],
-			api_levels_annotations_enabled: true,
-			api_levels_jar_filename: "android.other.jar",
-		}
-		`,
-		map[string][]byte{
-			"bar-doc/a.java": nil,
-		})
-	testcases := []struct {
-		moduleName          string
-		expectedJarFilename string
-		high_mem            bool
-	}{
-		{
-			moduleName:          "bar-stubs",
-			expectedJarFilename: "android.jar",
-			high_mem:            false,
-		},
-		{
-			moduleName:          "bar-stubs-other",
-			expectedJarFilename: "android.other.jar",
-			high_mem:            true,
-		},
-	}
-	for _, c := range testcases {
-		m := ctx.ModuleForTests(c.moduleName, "android_common")
-		metalava := m.Rule("metalava")
-		rp := metalava.RuleParams
-		expected := "--android-jar-pattern ./%/public/" + c.expectedJarFilename
-		if actual := rp.Command; !strings.Contains(actual, expected) {
-			t.Errorf("For %q, expected metalava argument %q, but was not found %q", c.moduleName, expected, actual)
-		}
-
-		if actual := rp.Pool != nil && strings.Contains(rp.Pool.String(), "highmem"); actual != c.high_mem {
-			t.Errorf("Expected %q high_mem to be %v, was %v", c.moduleName, c.high_mem, actual)
-		}
-	}
-}
-
-func TestDroidstubsWithSystemModules(t *testing.T) {
-	ctx, _ := testJava(t, `
-		droidstubs {
-		    name: "stubs-source-system-modules",
-		    srcs: [
-		        "bar-doc/a.java",
-		    ],
-				sdk_version: "none",
-				system_modules: "source-system-modules",
-		}
-
-		java_library {
-				name: "source-jar",
-		    srcs: [
-		        "a.java",
-		    ],
-		}
-
-		java_system_modules {
-				name: "source-system-modules",
-				libs: ["source-jar"],
-		}
-
-		droidstubs {
-		    name: "stubs-prebuilt-system-modules",
-		    srcs: [
-		        "bar-doc/a.java",
-		    ],
-				sdk_version: "none",
-				system_modules: "prebuilt-system-modules",
-		}
-
-		java_import {
-				name: "prebuilt-jar",
-				jars: ["a.jar"],
-		}
-
-		java_system_modules_import {
-				name: "prebuilt-system-modules",
-				libs: ["prebuilt-jar"],
-		}
-		`)
-
-	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-source-system-modules", "source-jar.jar")
-
-	checkSystemModulesUseByDroidstubs(t, ctx, "stubs-prebuilt-system-modules", "prebuilt-jar.jar")
-}
-
-func checkSystemModulesUseByDroidstubs(t *testing.T, ctx *android.TestContext, moduleName string, systemJar string) {
-	metalavaRule := ctx.ModuleForTests(moduleName, "android_common").Rule("metalava")
-	var systemJars []string
-	for _, i := range metalavaRule.Implicits {
-		systemJars = append(systemJars, i.Base())
-	}
-	if len(systemJars) < 1 || systemJars[0] != systemJar {
-		t.Errorf("inputs of %q must be []string{%q}, but was %#v.", moduleName, systemJar, systemJars)
-	}
-}
-
 func TestJarGenrules(t *testing.T) {
 	ctx, _ := testJava(t, `
 		java_library {