diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
index 4ada909..e1cb195 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
@@ -25,7 +25,10 @@
 import android.util.Log;
 
 import java.io.File;
-import java.io.RandomAccessFile;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Locale;
@@ -349,17 +352,21 @@
         // ad-hock ## HACK ##
         if (!Locale.ENGLISH.getLanguage().equals(locale.getLanguage())) return true;
 
+        FileInputStream inStream = null;
         try {
             // Read the version of the file
-            final RandomAccessFile raf = new RandomAccessFile(f, "r");
-            final int magic = raf.readInt();
+            inStream = new FileInputStream(f);
+            final ByteBuffer buffer = inStream.getChannel().map(
+                    FileChannel.MapMode.READ_ONLY, 0, f.length());
+            final int magic = buffer.getInt();
             if (magic != BinaryDictInputOutput.VERSION_2_MAGIC_NUMBER) {
                 return false;
             }
-            final int formatVersion = raf.readInt();
-            final int headerSize = raf.readInt();
+            final int formatVersion = buffer.getInt();
+            final int headerSize = buffer.getInt();
             final HashMap<String, String> options = CollectionUtils.newHashMap();
-            BinaryDictInputOutput.populateOptionsFromFile(raf, headerSize, options);
+            BinaryDictInputOutput.populateOptions(buffer, headerSize, options);
+
             final String version = options.get(VERSION_KEY);
             if (null == version) {
                 // No version in the options : the format is unexpected
@@ -374,6 +381,14 @@
             return false;
         } catch (NumberFormatException e) {
             return false;
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
         }
     }
 
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
index b23b7db..161b94c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -22,10 +22,13 @@
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 
 import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
@@ -307,33 +310,32 @@
         }
 
         /**
-         * Reads a string from a RandomAccessFile. This is the converse of the above method.
+         * Reads a string from a ByteBuffer. This is the converse of the above method.
          */
-        private static String readString(final RandomAccessFile source) throws IOException {
+        private static String readString(final ByteBuffer buffer) {
             final StringBuilder s = new StringBuilder();
-            int character = readChar(source);
+            int character = readChar(buffer);
             while (character != INVALID_CHARACTER) {
                 s.appendCodePoint(character);
-                character = readChar(source);
+                character = readChar(buffer);
             }
             return s.toString();
         }
 
         /**
-         * Reads a character from the file.
+         * Reads a character from the ByteBuffer.
          *
          * This follows the character format documented earlier in this source file.
          *
-         * @param source the file, positioned over an encoded character.
+         * @param buffer the buffer, positioned over an encoded character.
          * @return the character code.
          */
-        private static int readChar(RandomAccessFile source) throws IOException {
-            int character = source.readUnsignedByte();
+        private static int readChar(final ByteBuffer buffer) {
+            int character = readUnsignedByte(buffer);
             if (!fitsOnOneByte(character)) {
-                if (GROUP_CHARACTERS_TERMINATOR == character)
-                    return INVALID_CHARACTER;
+                if (GROUP_CHARACTERS_TERMINATOR == character) return INVALID_CHARACTER;
                 character <<= 16;
-                character += source.readUnsignedShort();
+                character += readUnsignedShort(buffer);
             }
             return character;
         }
@@ -1091,46 +1093,46 @@
     // readDictionaryBinary is the public entry point for them.
 
     static final int[] characterBuffer = new int[MAX_WORD_LENGTH];
-    private static CharGroupInfo readCharGroup(RandomAccessFile source,
-            final int originalGroupAddress) throws IOException {
+    private static CharGroupInfo readCharGroup(final ByteBuffer buffer,
+            final int originalGroupAddress) {
         int addressPointer = originalGroupAddress;
-        final int flags = source.readUnsignedByte();
+        final int flags = readUnsignedByte(buffer);
         ++addressPointer;
         final int characters[];
         if (0 != (flags & FLAG_HAS_MULTIPLE_CHARS)) {
             int index = 0;
-            int character = CharEncoding.readChar(source);
+            int character = CharEncoding.readChar(buffer);
             addressPointer += CharEncoding.getCharSize(character);
             while (-1 != character) {
                 characterBuffer[index++] = character;
-                character = CharEncoding.readChar(source);
+                character = CharEncoding.readChar(buffer);
                 addressPointer += CharEncoding.getCharSize(character);
             }
             characters = Arrays.copyOfRange(characterBuffer, 0, index);
         } else {
-            final int character = CharEncoding.readChar(source);
+            final int character = CharEncoding.readChar(buffer);
             addressPointer += CharEncoding.getCharSize(character);
             characters = new int[] { character };
         }
         final int frequency;
         if (0 != (FLAG_IS_TERMINAL & flags)) {
             ++addressPointer;
-            frequency = source.readUnsignedByte();
+            frequency = readUnsignedByte(buffer);
         } else {
             frequency = CharGroup.NOT_A_TERMINAL;
         }
         int childrenAddress = addressPointer;
         switch (flags & MASK_GROUP_ADDRESS_TYPE) {
         case FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
-            childrenAddress += source.readUnsignedByte();
+            childrenAddress += readUnsignedByte(buffer);
             addressPointer += 1;
             break;
         case FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
-            childrenAddress += source.readUnsignedShort();
+            childrenAddress += readUnsignedShort(buffer);
             addressPointer += 2;
             break;
         case FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
-            childrenAddress += (source.readUnsignedByte() << 16) + source.readUnsignedShort();
+            childrenAddress += readUnsignedInt24(buffer);
             addressPointer += 3;
             break;
         case FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
@@ -1140,38 +1142,38 @@
         }
         ArrayList<WeightedString> shortcutTargets = null;
         if (0 != (flags & FLAG_HAS_SHORTCUT_TARGETS)) {
-            final long pointerBefore = source.getFilePointer();
+            final int pointerBefore = buffer.position();
             shortcutTargets = new ArrayList<WeightedString>();
-            source.readUnsignedShort(); // Skip the size
+            buffer.getShort(); // Skip the size
             while (true) {
-                final int targetFlags = source.readUnsignedByte();
-                final String word = CharEncoding.readString(source);
+                final int targetFlags = readUnsignedByte(buffer);
+                final String word = CharEncoding.readString(buffer);
                 shortcutTargets.add(new WeightedString(word,
                         targetFlags & FLAG_ATTRIBUTE_FREQUENCY));
                 if (0 == (targetFlags & FLAG_ATTRIBUTE_HAS_NEXT)) break;
             }
-            addressPointer += (source.getFilePointer() - pointerBefore);
+            addressPointer += buffer.position() - pointerBefore;
         }
         ArrayList<PendingAttribute> bigrams = null;
         if (0 != (flags & FLAG_HAS_BIGRAMS)) {
             bigrams = new ArrayList<PendingAttribute>();
             while (true) {
-                final int bigramFlags = source.readUnsignedByte();
+                final int bigramFlags = readUnsignedByte(buffer);
                 ++addressPointer;
                 final int sign = 0 == (bigramFlags & FLAG_ATTRIBUTE_OFFSET_NEGATIVE) ? 1 : -1;
                 int bigramAddress = addressPointer;
                 switch (bigramFlags & MASK_ATTRIBUTE_ADDRESS_TYPE) {
                 case FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
-                    bigramAddress += sign * source.readUnsignedByte();
+                    bigramAddress += sign * readUnsignedByte(buffer);
                     addressPointer += 1;
                     break;
                 case FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
-                    bigramAddress += sign * source.readUnsignedShort();
+                    bigramAddress += sign * readUnsignedShort(buffer);
                     addressPointer += 2;
                     break;
                 case FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
-                    final int offset = ((source.readUnsignedByte() << 16)
-                            + source.readUnsignedShort());
+                    final int offset = (readUnsignedByte(buffer) << 16)
+                            + readUnsignedShort(buffer);
                     bigramAddress += sign * offset;
                     addressPointer += 3;
                     break;
@@ -1188,15 +1190,15 @@
     }
 
     /**
-     * Reads and returns the char group count out of a file and forwards the pointer.
+     * Reads and returns the char group count out of a buffer and forwards the pointer.
      */
-    private static int readCharGroupCount(RandomAccessFile source) throws IOException {
-        final int msb = source.readUnsignedByte();
+    private static int readCharGroupCount(final ByteBuffer buffer) {
+        final int msb = readUnsignedByte(buffer);
         if (MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT >= msb) {
             return msb;
         } else {
             return ((MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT & msb) << 8)
-                    + source.readUnsignedByte();
+                    + readUnsignedByte(buffer);
         }
     }
 
@@ -1204,31 +1206,29 @@
     // of this method. Since it performs direct, unbuffered random access to the file and
     // may be called hundreds of thousands of times, the resulting performance is not
     // reasonable without some kind of cache. Thus:
-    // TODO: perform buffered I/O here and in other places in the code.
     private static TreeMap<Integer, String> wordCache = new TreeMap<Integer, String>();
     /**
      * Finds, as a string, the word at the address passed as an argument.
      *
-     * @param source the file to read from.
+     * @param buffer the buffer to read from.
      * @param headerSize the size of the header.
      * @param address the address to seek.
      * @return the word, as a string.
-     * @throws IOException if the file can't be read.
      */
-    private static String getWordAtAddress(final RandomAccessFile source, final long headerSize,
-            int address) throws IOException {
+    private static String getWordAtAddress(final ByteBuffer buffer, final int headerSize,
+            final int address) {
         final String cachedString = wordCache.get(address);
         if (null != cachedString) return cachedString;
-        final long originalPointer = source.getFilePointer();
-        source.seek(headerSize);
-        final int count = readCharGroupCount(source);
+        final int originalPointer = buffer.position();
+        buffer.position(headerSize);
+        final int count = readCharGroupCount(buffer);
         int groupOffset = getGroupCountSize(count);
         final StringBuilder builder = new StringBuilder();
         String result = null;
 
         CharGroupInfo last = null;
         for (int i = count - 1; i >= 0; --i) {
-            CharGroupInfo info = readCharGroup(source, groupOffset);
+            CharGroupInfo info = readCharGroup(buffer, groupOffset);
             groupOffset = info.mEndAddress;
             if (info.mOriginalAddress == address) {
                 builder.append(new String(info.mCharacters, 0, info.mCharacters.length));
@@ -1239,9 +1239,9 @@
                 if (info.mChildrenAddress > address) {
                     if (null == last) continue;
                     builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
-                    source.seek(last.mChildrenAddress + headerSize);
+                    buffer.position(last.mChildrenAddress + headerSize);
                     groupOffset = last.mChildrenAddress + 1;
-                    i = source.readUnsignedByte();
+                    i = readUnsignedByte(buffer);
                     last = null;
                     continue;
                 }
@@ -1249,14 +1249,14 @@
             }
             if (0 == i && hasChildrenAddress(last.mChildrenAddress)) {
                 builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
-                source.seek(last.mChildrenAddress + headerSize);
+                buffer.position(last.mChildrenAddress + headerSize);
                 groupOffset = last.mChildrenAddress + 1;
-                i = source.readUnsignedByte();
+                i = readUnsignedByte(buffer);
                 last = null;
                 continue;
             }
         }
-        source.seek(originalPointer);
+        buffer.position(originalPointer);
         wordCache.put(address, result);
         return result;
     }
@@ -1269,44 +1269,47 @@
      * This will recursively read other nodes into the structure, populating the reverse
      * maps on the fly and using them to keep track of already read nodes.
      *
-     * @param source the data file, correctly positioned at the start of a node.
+     * @param buffer the buffer, correctly positioned at the start of a node.
      * @param headerSize the size, in bytes, of the file header.
      * @param reverseNodeMap a mapping from addresses to already read nodes.
      * @param reverseGroupMap a mapping from addresses to already read character groups.
      * @return the read node with all his children already read.
      */
-    private static Node readNode(RandomAccessFile source, long headerSize,
-            Map<Integer, Node> reverseNodeMap, Map<Integer, CharGroup> reverseGroupMap)
+    private static Node readNode(final ByteBuffer buffer, final int headerSize,
+            final Map<Integer, Node> reverseNodeMap, final Map<Integer, CharGroup> reverseGroupMap)
             throws IOException {
-        final int nodeOrigin = (int)(source.getFilePointer() - headerSize);
-        final int count = readCharGroupCount(source);
+        final int nodeOrigin = buffer.position() - headerSize;
+        final int count = readCharGroupCount(buffer);
         final ArrayList<CharGroup> nodeContents = new ArrayList<CharGroup>();
         int groupOffset = nodeOrigin + getGroupCountSize(count);
         for (int i = count; i > 0; --i) {
-            CharGroupInfo info = readCharGroup(source, groupOffset);
+            CharGroupInfo info =readCharGroup(buffer, groupOffset);
             ArrayList<WeightedString> shortcutTargets = info.mShortcutTargets;
             ArrayList<WeightedString> bigrams = null;
             if (null != info.mBigrams) {
                 bigrams = new ArrayList<WeightedString>();
                 for (PendingAttribute bigram : info.mBigrams) {
-                    final String word = getWordAtAddress(source, headerSize, bigram.mAddress);
+                    final String word = getWordAtAddress(
+                            buffer, headerSize, bigram.mAddress);
                     bigrams.add(new WeightedString(word, bigram.mFrequency));
                 }
             }
             if (hasChildrenAddress(info.mChildrenAddress)) {
                 Node children = reverseNodeMap.get(info.mChildrenAddress);
                 if (null == children) {
-                    final long currentPosition = source.getFilePointer();
-                    source.seek(info.mChildrenAddress + headerSize);
-                    children = readNode(source, headerSize, reverseNodeMap, reverseGroupMap);
-                    source.seek(currentPosition);
+                    final int currentPosition = buffer.position();
+                    buffer.position(info.mChildrenAddress + headerSize);
+                    children = readNode(
+                            buffer, headerSize, reverseNodeMap, reverseGroupMap);
+                    buffer.position(currentPosition);
                 }
                 nodeContents.add(
-                        new CharGroup(info.mCharacters, shortcutTargets, bigrams, info.mFrequency,
-                                children));
+                        new CharGroup(info.mCharacters, shortcutTargets,
+                                bigrams, info.mFrequency, children));
             } else {
                 nodeContents.add(
-                        new CharGroup(info.mCharacters, shortcutTargets, bigrams, info.mFrequency));
+                        new CharGroup(info.mCharacters, shortcutTargets,
+                                bigrams, info.mFrequency));
             }
             groupOffset = info.mEndAddress;
         }
@@ -1318,12 +1321,13 @@
 
     /**
      * Helper function to get the binary format version from the header.
+     * @throws IOException
      */
-    private static int getFormatVersion(final RandomAccessFile source) throws IOException {
-        final int magic_v1 = source.readUnsignedShort();
-        if (VERSION_1_MAGIC_NUMBER == magic_v1) return source.readUnsignedByte();
-        final int magic_v2 = (magic_v1 << 16) + source.readUnsignedShort();
-        if (VERSION_2_MAGIC_NUMBER == magic_v2) return source.readUnsignedShort();
+    private static int getFormatVersion(final ByteBuffer buffer) throws IOException {
+        final int magic_v1 = readUnsignedShort(buffer);
+        if (VERSION_1_MAGIC_NUMBER == magic_v1) return readUnsignedByte(buffer);
+        final int magic_v2 = (magic_v1 << 16) + readUnsignedShort(buffer);
+        if (VERSION_2_MAGIC_NUMBER == magic_v2) return readUnsignedShort(buffer);
         return NOT_A_VERSION_NUMBER;
     }
 
@@ -1333,53 +1337,60 @@
      * The file is read at the current file pointer, so the caller must take care the pointer
      * is in the right place before calling this.
      */
-    public static void populateOptionsFromFile(final RandomAccessFile source, final long headerSize,
-            final HashMap<String, String> options) throws IOException {
-        while (source.getFilePointer() < headerSize) {
-            final String key = CharEncoding.readString(source);
-            final String value = CharEncoding.readString(source);
+    public static void populateOptions(final ByteBuffer buffer, final int headerSize,
+            final HashMap<String, String> options) {
+        while (buffer.position() < headerSize) {
+            final String key = CharEncoding.readString(buffer);
+            final String value = CharEncoding.readString(buffer);
             options.put(key, value);
         }
     }
 
     /**
-     * Reads a random access file and returns the memory representation of the dictionary.
+     * Reads a byte buffer and returns the memory representation of the dictionary.
      *
      * This high-level method takes a binary file and reads its contents, populating a
      * FusionDictionary structure. The optional dict argument is an existing dictionary to
      * which words from the file should be added. If it is null, a new dictionary is created.
      *
-     * @param source the file to read.
+     * @param buffer the buffer to read.
      * @param dict an optional dictionary to add words to, or null.
      * @return the created (or merged) dictionary.
      */
-    public static FusionDictionary readDictionaryBinary(final RandomAccessFile source,
+    public static FusionDictionary readDictionaryBinary(final ByteBuffer buffer,
             final FusionDictionary dict) throws IOException, UnsupportedFormatException {
         // Check file version
-        final int version = getFormatVersion(source);
-        if (version < MINIMUM_SUPPORTED_VERSION || version > MAXIMUM_SUPPORTED_VERSION ) {
+        final int version = getFormatVersion(buffer);
+        if (version < MINIMUM_SUPPORTED_VERSION || version > MAXIMUM_SUPPORTED_VERSION) {
             throw new UnsupportedFormatException("This file has version " + version
                     + ", but this implementation does not support versions above "
                     + MAXIMUM_SUPPORTED_VERSION);
         }
 
-        // Read options
-        final int optionsFlags = source.readUnsignedShort();
+        // clear cache
+        wordCache.clear();
 
-        final long headerSize;
+        // Read options
+        final int optionsFlags = readUnsignedShort(buffer);
+
+        final int headerSize;
         final HashMap<String, String> options = new HashMap<String, String>();
         if (version < FIRST_VERSION_WITH_HEADER_SIZE) {
-            headerSize = source.getFilePointer();
+            headerSize = buffer.position();
         } else {
-            headerSize = (source.readUnsignedByte() << 24) + (source.readUnsignedByte() << 16)
-                    + (source.readUnsignedByte() << 8) + source.readUnsignedByte();
-            populateOptionsFromFile(source, headerSize, options);
-            source.seek(headerSize);
+            headerSize = buffer.getInt();
+            populateOptions(buffer, headerSize, options);
+            buffer.position(headerSize);
+        }
+
+        if (headerSize < 0) {
+            throw new UnsupportedFormatException("header size can't be negative.");
         }
 
         Map<Integer, Node> reverseNodeMapping = new TreeMap<Integer, Node>();
         Map<Integer, CharGroup> reverseGroupMapping = new TreeMap<Integer, CharGroup>();
-        final Node root = readNode(source, headerSize, reverseNodeMapping, reverseGroupMapping);
+        final Node root = readNode(
+                buffer, headerSize, reverseNodeMapping, reverseGroupMapping);
 
         FusionDictionary newDict = new FusionDictionary(root,
                 new FusionDictionary.DictionaryOptions(options,
@@ -1403,6 +1414,28 @@
     }
 
     /**
+     * Helper function to read one byte from ByteBuffer.
+     */
+    private static int readUnsignedByte(final ByteBuffer buffer) {
+        return ((int)buffer.get()) & 0xFF;
+    }
+
+    /**
+     * Helper function to read two byte from ByteBuffer.
+     */
+    private static int readUnsignedShort(final ByteBuffer buffer) {
+        return ((int)buffer.getShort()) & 0xFFFF;
+    }
+
+    /**
+     * Helper function to read three byte from ByteBuffer.
+     */
+    private static int readUnsignedInt24(final ByteBuffer buffer) {
+        final int value = readUnsignedByte(buffer) << 16;
+        return value + readUnsignedShort(buffer);
+    }
+
+    /**
      * Basic test to find out whether the file is a binary dictionary or not.
      *
      * Concretely this only tests the magic number.
@@ -1411,14 +1444,26 @@
      * @return true if it's a binary dictionary, false otherwise
      */
     public static boolean isBinaryDictionary(final String filename) {
+        FileInputStream inStream = null;
         try {
-            RandomAccessFile f = new RandomAccessFile(filename, "r");
-            final int version = getFormatVersion(f);
+            final File file = new File(filename);
+            inStream = new FileInputStream(file);
+            final ByteBuffer buffer = inStream.getChannel().map(
+                    FileChannel.MapMode.READ_ONLY, 0, file.length());
+            final int version = getFormatVersion(buffer);
             return (version >= MINIMUM_SUPPORTED_VERSION && version <= MAXIMUM_SUPPORTED_VERSION);
         } catch (FileNotFoundException e) {
             return false;
         } catch (IOException e) {
             return false;
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
         }
     }
 
diff --git a/tests/src/com/android/inputmethod/latin/BinaryDictIOTests.java b/tests/src/com/android/inputmethod/latin/BinaryDictIOTests.java
new file mode 100644
index 0000000..0094db8
--- /dev/null
+++ b/tests/src/com/android/inputmethod/latin/BinaryDictIOTests.java
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * 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 com.android.inputmethod.latin;
+
+import com.android.inputmethod.latin.makedict.BinaryDictInputOutput;
+import com.android.inputmethod.latin.makedict.FusionDictionary;
+import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
+
+import android.test.AndroidTestCase;
+import android.util.Log;
+import android.util.SparseArray;
+
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Random;
+import java.util.Set;
+
+/**
+ * Unit tests for BinaryDictInputOutput
+ */
+public class BinaryDictIOTests extends AndroidTestCase {
+    private static final String TAG = BinaryDictIOTests.class.getSimpleName();
+    private static final int MAX_UNIGRAMS = 1000;
+    private static final int UNIGRAM_FREQ = 10;
+    private static final int BIGRAM_FREQ = 50;
+
+    private static final String[] CHARACTERS =
+        {
+        "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
+        "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"
+        };
+
+    /**
+     * Generates a random word.
+     */
+    private String generateWord(final int value) {
+        final int lengthOfChars = CHARACTERS.length;
+        StringBuilder builder = new StringBuilder("a");
+        long lvalue = Math.abs((long)value);
+        while (lvalue > 0) {
+            builder.append(CHARACTERS[(int)(lvalue % lengthOfChars)]);
+            lvalue /= lengthOfChars;
+        }
+        return builder.toString();
+    }
+
+    private List<String> generateWords(final int number, final Random random) {
+        final Set<String> wordSet = CollectionUtils.newHashSet();
+        while (wordSet.size() < number) {
+            wordSet.add(generateWord(random.nextInt()));
+        }
+        return new ArrayList<String>(wordSet);
+    }
+
+    private void addUnigrams(final int number,
+            final FusionDictionary dict,
+            final List<String> words) {
+        for (int i = 0; i < number; ++i) {
+            final String word = words.get(i);
+            dict.add(word, UNIGRAM_FREQ, null);
+        }
+    }
+
+    private void addBigrams(final FusionDictionary dict,
+            final List<String> words,
+            final SparseArray<List<Integer>> sparseArray) {
+        for (int i = 0; i < sparseArray.size(); ++i) {
+            final int w1 = sparseArray.keyAt(i);
+            for (int w2 : sparseArray.valueAt(i)) {
+                dict.setBigram(words.get(w1), words.get(w2), BIGRAM_FREQ);
+            }
+        }
+    }
+
+    private long timeWritingDictToFile(final String fileName,
+            final FusionDictionary dict) {
+
+        final File file = new File(getContext().getFilesDir(), fileName);
+        long now = -1, diff = -1;
+
+        try {
+            final FileOutputStream out = new FileOutputStream(file);
+
+            now = System.currentTimeMillis();
+            BinaryDictInputOutput.writeDictionaryBinary(out, dict, 2);
+            diff = System.currentTimeMillis() - now;
+
+            out.flush();
+            out.close();
+        } catch (IOException e) {
+            Log.e(TAG, "IO exception while writing file: " + e);
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "UnsupportedFormatException: " + e);
+        }
+
+        return diff;
+    }
+
+    private void checkDictionary(final FusionDictionary dict,
+            final List<String> words,
+            final SparseArray<List<Integer>> bigrams) {
+        assertNotNull(dict);
+
+        // check unigram
+        for (final String word : words) {
+            final CharGroup cg = FusionDictionary.findWordInTree(dict.mRoot, word);
+            assertNotNull(cg);
+        }
+
+        // check bigram
+        for (int i = 0; i < bigrams.size(); ++i) {
+            final int w1 = bigrams.keyAt(i);
+            for (final int w2 : bigrams.valueAt(i)) {
+                final CharGroup cg = FusionDictionary.findWordInTree(dict.mRoot, words.get(w1));
+                assertNotNull(words.get(w1) + "," + words.get(w2), cg.getBigram(words.get(w2)));
+            }
+        }
+    }
+
+    private long timeReadingAndCheckDict(final String fileName,
+            final List<String> words,
+            final SparseArray<List<Integer>> bigrams) {
+
+        long now, diff = -1;
+
+        try {
+            final File file = new File(getContext().getFilesDir(), fileName);
+            final FileInputStream inStream = new FileInputStream(file);
+            final ByteBuffer buffer = inStream.getChannel().map(
+                    FileChannel.MapMode.READ_ONLY, 0, file.length());
+
+            now = System.currentTimeMillis();
+
+            final FusionDictionary dict =
+                    BinaryDictInputOutput.readDictionaryBinary(buffer, null);
+
+            diff = System.currentTimeMillis() - now;
+
+            checkDictionary(dict, words, bigrams);
+            return diff;
+
+        } catch (IOException e) {
+            Log.e(TAG, "raise IOException while reading file " + e);
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "Unsupported format: " + e);
+        }
+
+        return diff;
+    }
+
+    private String runReadAndWrite(final List<String> words,
+            final SparseArray<List<Integer>> bigrams,
+            final String message) {
+        final FusionDictionary dict = new FusionDictionary(new Node(),
+                new FusionDictionary.DictionaryOptions(
+                        new HashMap<String,String>(), false, false));
+
+        final String fileName = generateWord((int)System.currentTimeMillis()) + ".dict";
+
+        addUnigrams(words.size(), dict, words);
+        addBigrams(dict, words, bigrams);
+        // check original dictionary
+        checkDictionary(dict, words, bigrams);
+
+        final long write = timeWritingDictToFile(fileName, dict);
+        final long read = timeReadingAndCheckDict(fileName, words, bigrams);
+        deleteFile(fileName);
+
+        return "PROF: read=" + read + "ms, write=" + write + "ms    :" + message;
+    }
+
+    private void deleteFile(final String fileName) {
+        final File file = new File(getContext().getFilesDir(), fileName);
+        file.delete();
+    }
+
+    public void testReadAndWrite() {
+        final List<String> results = new ArrayList<String>();
+
+        final Random random = new Random(123456);
+        final List<String> words = generateWords(MAX_UNIGRAMS, random);
+        final SparseArray<List<Integer>> emptyArray = CollectionUtils.newSparseArray();
+
+        final SparseArray<List<Integer>> chain = CollectionUtils.newSparseArray();
+        for (int i = 0; i < words.size(); ++i) chain.put(i, new ArrayList<Integer>());
+        for (int i = 1; i < words.size(); ++i) chain.get(i-1).add(i);
+
+        final SparseArray<List<Integer>> star = CollectionUtils.newSparseArray();
+        final List<Integer> list0 = CollectionUtils.newArrayList();
+        star.put(0, list0);
+        for (int i = 1; i < words.size(); ++i) star.get(0).add(i);
+
+        results.add(runReadAndWrite(words, emptyArray, "only unigram"));
+        results.add(runReadAndWrite(words, chain, "chain"));
+        results.add(runReadAndWrite(words, star, "star"));
+
+        for (final String result : results) {
+            Log.d(TAG, result);
+        }
+    }
+}
diff --git a/tools/dicttool/src/android/inputmethod/latin/dicttool/DictionaryMaker.java b/tools/dicttool/src/android/inputmethod/latin/dicttool/DictionaryMaker.java
index 25e1740..fbfc1da 100644
--- a/tools/dicttool/src/android/inputmethod/latin/dicttool/DictionaryMaker.java
+++ b/tools/dicttool/src/android/inputmethod/latin/dicttool/DictionaryMaker.java
@@ -27,7 +27,8 @@
 import java.io.FileOutputStream;
 import java.io.FileWriter;
 import java.io.IOException;
-import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
 import java.util.Arrays;
 import java.util.LinkedList;
 
@@ -238,8 +239,23 @@
      */
     private static FusionDictionary readBinaryFile(final String binaryFilename)
             throws FileNotFoundException, IOException, UnsupportedFormatException {
-        final RandomAccessFile inputFile = new RandomAccessFile(binaryFilename, "r");
-        return BinaryDictInputOutput.readDictionaryBinary(inputFile, null);
+        FileInputStream inStream = null;
+
+        try {
+            final File file = new File(binaryFilename);
+            inStream = new FileInputStream(file);
+            final ByteBuffer buffer = inStream.getChannel().map(
+                    FileChannel.MapMode.READ_ONLY, 0, file.length());
+            return BinaryDictInputOutput.readDictionaryBinary(buffer, null);
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
     }
 
     /**