Adapt between Android's Context.openFile{Input,Output} and its mode support, and Guava's sinks and sources.

AndroidPrivateFileGuavaAdapter.java

// Available under the MIT license, http://opensource.org/licenses/MIT
/**
 * Adapt between Context's file input/output streams and Guava's sinks and sources.
 *
 * This supports file modes.
 *
 * Usage:
 *   ByteSink sink =
 *     new AndroidPrivateFileGuavaAdapter(
 *       "foo", Context.MODE_PRIVATE, context).asByteSink();
 */
public class AndroidPrivateFileGuavaAdapter {

  private final String mName;
  private final int mMode;
  private final Context mContext;

  public AndroidPrivateFileHelper(String name, int mode, Context context) {
    mName = name;
    mMode = mode;
    mContext = context.getApplicationContext();
  }

  public ByteSink asByteSink() {
    return new ByteSink() {
      public OutputStream openStream() throws IOException {
        return mContext.openFileOutput(mName, mMode);
      }
    };
  }

  public ByteSource asByteSource() {
    return new ByteSource() {
      public InputStream openStream() throws IOException {
        return mContext.openFileInput(mName);
      }
    };
  }

  public CharSink asCharSink() {
    return asByteSink().asCharSink(Charsets.UTF_8);
  }

  public CharSource asCharSource() {
    return asByteSource().asCharSource(Charsets.UTF_8);
  }
}