android的Environment类

public static File getExternalStoragePublicDirectory (String type)

Since: API Level 8

Get a top-level public external storage directory for placing files of a particular type. This is where the user will typically place and manage their own files, so you should be careful about what you put here to ensure you don‘t erase their files or get in the way of their own organization.

Here is an example of typical code to manipulate a picture on the public external storage:

void createExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user‘s
    // public pictures directory.  Note that you should be careful about
    // what you place here, since the user often manages these files.  For
    // pictures and other media owned by the application, consider
    // Context.getExternalMediaDir().
    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");

    try {
        // Make sure the Pictures directory exists.
        path.mkdirs();

        // Very simple code to copy a picture from the application‘s
        // resource into the external file.  Note that this code does
        // no error checking, and assumes the picture is small (does not
        // try to copy it in chunks).  Note that if external storage is
        // not currently mounted this will silently fail.
        InputStream is = getResources().openRawResource(R.drawable.balloons);
        OutputStream os = new FileOutputStream(file);
        byte[] data = new byte[is.available()];
        is.read(data);
        os.write(data);
        is.close();
        os.close();

        // Tell the media scanner about the new file so that it is // 这一步非常重要！！
        // immediately available to the user.
        MediaScannerConnection.scanFile(this,
                new String[] { file.toString() }, null,
                new MediaScannerConnection.OnScanCompletedListener() {
            public void onScanCompleted(String path, Uri uri) {
                Log.i("ExternalStorage", "Scanned " + path + ":");
                Log.i("ExternalStorage", "-> uri=" + uri);
            }
        });
    } catch (IOException e) {
        // Unable to create file, likely because external storage is
        // not currently mounted.
        Log.w("ExternalStorage", "Error writing " + file, e);
    }
}

void deleteExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user‘s
    // public pictures directory and delete the file.  If external
    // storage is not currently mounted this will fail.
    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");
    file.delete();
}

boolean hasExternalStoragePublicPicture() {
    // Create a path where we will place our picture in the user‘s
    // public pictures directory and check if the file exists.  If
    // external storage is not currently mounted this will think the
    // picture doesn‘t exist.
    File path = Environment.getExternalStoragePublicDirectory(
            Environment.DIRECTORY_PICTURES);
    File file = new File(path, "DemoPicture.jpg");
    return file.exists();
}

Parameters

Returns

• Returns the File path for the directory. Note that this directory may not yet exist, so you must make sure it exists before using it such as withFile.mkdirs().

http://blog.csdn.net/aiqing0119/article/details/7718494