An example analysis of the third-level caching mechanism of Android pictures

public class ImageCacheUtil {
  private LruCache<String, Bitmap> lruCache;
  private File cacheDir;
  private ExecutorService newFixedThreadPool;
  private Handler handler;
  public static final int SUCCESS = 100;
  public static final int FAIL = 101;
  //When we get the picture, we have three steps  //1. Get the picture from the cache  //2. Get the image from the local cache directory and after obtaining it, put it in the cache  //3. Download the picture from the network, and after the download is completed, save it to the local cache directory and put it in the cache  public ImageCacheUtil(Context context,Handler handler){
    //Get the cache size    int maxsize = (int) (().maxMemory()/8);
    //maxSize: Set the maximum cache space    lruCache = new LruCache<String, Bitmap>(maxsize){
      //Get the space occupied by the moved out image. When the image is moved out, the cache space occupied by the image needs to be moved out of the cache.       @Override
      protected int sizeOf(String key, Bitmap value) {
         //Calculate the cache size occupied by the picture         //getRowBytes: Get the size occupied by a line of the image         //getHeight: Get the number of rows occupied by the picture        return ()*();
      }
    };
    //Get cache directory    cacheDir = ();
    //Get thread pool    //nThreads: Number of threads in the thread pool    newFixedThreadPool = (5);
     = handler;
  }
  /**
    * Methods to get pictures
    * @param url
    * @param positon
    * @return
    */
  public Bitmap getBitmap(String url,int position){
    Bitmap bitmap = null;
    //1. Get the image from the cache (LRUCache<k,v>) k:key Save the image mark, generally the url address of the image, v:value picture    bitmap = (url);//Get the corresponding picture from the cache according to the key    //(url, bitmap): Save the image to cache    if (bitmap!=null) {
      return bitmap;
    }
    //2. Get the image from the local cache directory and after obtaining it, put it in the cache    bitmap = getFromLocal(url);
    if (bitmap!=null) {
      return bitmap;
    }
    //3. Download the picture from the network, and after the download is completed, save it to the local cache directory and put it in the cache    getFromNet(url,position);
    return null;
  }
  /**
    * Download pictures from the network, asynchronous methods, thread pools
    * @param url
    * @param position
    */
  private void getFromNet(String url, int position) {
    (new RunnableTask(url,position));
  }
  class RunnableTask implements Runnable{
    private String imageUrl;
    private int position;
    public RunnableTask(String url,int position){
       = url;
       = position;
    }

    @Override
    public void run() {
      Message message = ();
      //Download pictures      try {
        URL url = new URL(imageUrl);
        HttpURLConnection conn = (HttpURLConnection) ();
        (3000);
        (5000);
        ("GET");
        InputStream inputStream = ();
        Bitmap bitmap = (inputStream);
        //Save to local cache        wirteToLocal(imageUrl, bitmap);
        //Save to system buffer        (imageUrl, bitmap);
        //Show the picture and send a message to the handler         = SUCCESS;
         = bitmap;
        message.arg1 = position;
        (message);
        return;
      } catch (Exception e) {
        ();
      }
       = FAIL;
      (message);
    }
  }
  /**
    * Get pictures from local cache directory
    * @param url
    */
  private Bitmap getFromLocal(String url) {
    //Get the picture based on the name of the picture    try {
      String fileName = (url).substring(10);
      File file = new File(cacheDir, fileName);
      Bitmap bitmap = (());
      //Anti-theft cache is in      (url, bitmap);
      return bitmap;
    } catch (Exception e) {
      ();
    }
    return null;
  }
  /**
    * Save the image to the local cache directory
    */
  public void wirteToLocal(String url,Bitmap bitmap){
    //url name, encrypted by MD5, and intercept the first 10 digits as names    try {
      String fileName = (url).substring(10);
      File file = new File(cacheDir, fileName);
      FileOutputStream out = new FileOutputStream(file);
      //format: The format of the picture (there are many pngs used in Android because the quality of the png will not change)      //quality: compression ratio      //stream: Stream information      (, 100, out);//Save the image to that location    } catch (Exception e) {
      ();
    }
  }

}

public class MD5Encoder {

  public static String encode(String string) throws Exception {
    byte[] hash = ("MD5").digest(("UTF-8"));
    StringBuilder hex = new StringBuilder( * 2);
    for (byte b : hash) {
      if ((b & 0xFF) < 0x10) {
        ("0");
      }
      ((b & 0xFF));
    }
    return ();
  }
}

ImageCacheUtil imageCacheUtil = new ImageCacheUtil(getApplicationContext, handler);

private Handler handler = new Handler(){
  public void handleMessage( msg) {
    switch () {
    case :
      //Set pictures for the control      Bitmap bitmap = (Bitmap) ;
      int position = msg.arg1;
      ImageView image= (ImageView) (position);//It is to obtain the corresponding control based on the position of the entry      if (image != null && bitmap != null) {
        (bitmap);
      }
      break;
    case :
      (getApplicationContext, "Image download failed", 0).show();
      break;
    }
  };
};

Bitmap bitmap = ((position).listimage, position);
if (bitmap != null) {
  (bitmap);
}