安卓，DiskLruChche，不能存取到bitmap的内容，求指教

Question

布局就只有一个imageview，不贴了.

以下是mainactivity,只贴有关的部分，avd是安卓6.0

 public class MainActivity extends AppCompatActivity 
 {

    ImageView imageView;
    File file;                             //cache的位置
    DiskLruCache mDiskLruCache;
    DiskLruCache.Editor editor;
    URL imgurl;
    HttpURLConnection con;
    OutputStream editorOutput;            //editor的输出流
    InputStream in;                        //从网络获取的输入流
    DiskLruCache.Snapshot snapshot;
    Bitmap bitmap;
    Handler handler;


        //子线程已获取到bitmap时发消息给主线程
        class MyHandler extends Handler
    {
        public void handleMessage(Message msg)
        {
            switch(msg.arg1)
            {
                case 1:

                    imageView.setImageBitmap(bitmap);
                    Log.e("this","已接受到消息");

            }
        }
        }

        //计算md5
    public String hashKeyForDisk(String key)
    {
          String cacheKey;
          try {
                 final MessageDigest mDigest = MessageDigest.getInstance("MD5");
                 mDigest.update(key.getBytes());
                   cacheKey = bytesToHexString(mDigest.digest());
               } catch (NoSuchAlgorithmException e) {
                cacheKey = String.valueOf(key.hashCode());
             }
          return cacheKey;
    }

    private String bytesToHexString(byte[] bytes) {
          StringBuilder sb = new StringBuilder();
          for (int i = 0; i < bytes.length; i++) {
                 String hex = Integer.toHexString(0xFF & bytes[i]);
                if (hex.length() == 1) {
                        sb.append('0');
                     }
                 sb.append(hex);
              }
           return sb.toString();
        }


    class myThread extends Thread
    {
        public void run() {
           // String path = getExternalCacheDir().getPath();
            String path=Environment.getExternalStorageDirectory().getPath();
            file = new File(path + "/mytest");
            if (!file.exists())  file.mkdirs();
            try {
                mDiskLruCache = DiskLruCache.open(file, 1, 1, 50 * 1024 * 1024);


                String url = "http://v1.qzone.cc/skin/201310/08/17/19/5253ce06a29c2425.jpg%21600x600.jpg";
                String key = hashKeyForDisk(url);


                editor = mDiskLruCache.edit(key);
                editorOutput = editor.newOutputStream(0);

                //从网络获取数据流
                imgurl = new URL(url);
                con = (HttpURLConnection) imgurl.openConnection();
                in = con.getInputStream();
                int b;

                                 //把输入流写到editor的输出流
                while ((b = in.read()) != 0) editorOutput.write(b);       
                editorOutput.flush();
                con.disconnect();

                editor.commit();
                mDiskLruCache.flush();


                //从缓存中读取bitmap
                snapshot = mDiskLruCache.get(key);
                if (snapshot != null) {
                    FileInputStream is = (FileInputStream) snapshot.getInputStream(0);
                    bitmap = BitmapFactory.decodeStream(is);
                    Message msg = handler.obtainMessage();
                    msg.arg1 = 1;
                    handler.sendMessage(msg);
                } else {
                    Log.e("this", "snapshot为空");
                }
            } catch (Exception e) {
                Log.e("this",  e.toString());
            }
        }

    }


        @Override
    protected void onCreate(Bundle savedInstanceState) 
        {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

                int REQUEST_EXTERNAL_STORAGE=1;
        String[] PERMISSIONS_STORAGE={Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE};

        ActivityCompat.requestPermissions(this, PERMISSIONS_STORAGE, REQUEST_EXTERNAL_STORAGE);

        Log.e("this", "已拿到权限");

        handler=new MyHandler();


        imageView = (ImageView) MainActivity.this.findViewById(R.id.imageview);

        Thread thread=new myThread();
        thread.start();


        }
}

下面再贴贴manifest中的权限

 <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.INTERNET"/>

代码如上，运行效果如下

我试过直接从网络获取的流中直接获取bitmap是可以的，而这样先用DiskLruCache存了再取回来就不行，求大神指点指点