diff --git a/jar/jar.go b/jar/jar.go
new file mode 100644
index 0000000..d8f063c
--- /dev/null
+++ b/jar/jar.go
@@ -0,0 +1,55 @@
+// Copyright 2017 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 jar
+
+import (
+	"fmt"
+	"strings"
+)
+
+// EntryNamesLess tells whether <filepathA> should precede <filepathB> in
+// the order of files with a .jar
+func EntryNamesLess(filepathA string, filepathB string) (less bool) {
+	diff := index(filepathA) - index(filepathB)
+	if diff == 0 {
+		return filepathA < filepathB
+	}
+	return diff < 0
+}
+
+// Treats trailing * as a prefix match
+func patternMatch(pattern, name string) bool {
+	if strings.HasSuffix(pattern, "*") {
+		return strings.HasPrefix(name, strings.TrimSuffix(pattern, "*"))
+	} else {
+		return name == pattern
+	}
+}
+
+var jarOrder = []string{
+	"META-INF/",
+	"META-INF/MANIFEST.MF",
+	"META-INF/*",
+	"*",
+}
+
+func index(name string) int {
+	for i, pattern := range jarOrder {
+		if patternMatch(pattern, name) {
+			return i
+		}
+	}
+	panic(fmt.Errorf("file %q did not match any pattern", name))
+}