<!-- sdcard权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"></uses-permission>

private final static String PATH = "/sdcard/digu";
private final static String FILENAME = "/notes.txt";

/**
* 写文件
*/
private void onWrite() {
   try {
     Log.d(LOG_TAG, "Start Write");
     //1.判断是否存在sdcard
     if (Environment.MEDIA_MOUNTED.equals(Environment
         .getExternalStorageState())) {
       //目录
       File path = new File(PATH);
       //文件
       File f = new File(PATH + FILENAME);
       if(!path.exists()){
         //2.创建目录，可以在应用启动的时候创建
         path.mkdirs();
       }
       if (!f.exists()) {
         //3.创建文件
         f.createNewFile();
       }
       OutputStreamWriter osw = new OutputStreamWriter(
           new FileOutputStream(f));
       //4.写文件，从EditView获得文本值
       osw.write(editor.getText().toString());
       osw.close();
     }
   } catch (Exception e) {
     Log.d(LOG_TAG, "file create error");
   }
 }