Android实现图片异步加载并缓存到本地

MemoryCache.java

import java.lang.ref.SoftReference; 
import java.util.Collections; 
import java.util.HashMap; 
import java.util.Map; 
import android.graphics.Bitmap; 
 
public class MemoryCache { 
  private Map<String, SoftReference<Bitmap>> cache = Collections 
      .synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());// 软引用 
 
  public Bitmap get(String id) { 
    if (!cache.containsKey(id)) 
      return null; 
    SoftReference<Bitmap> ref = cache.get(id); 
    return ref.get(); 
  } 
 
  public void put(String id, Bitmap bitmap) { 
    cache.put(id, new SoftReference<Bitmap>(bitmap)); 
  } 
 
  public void clear() { 
    cache.clear(); 
  } 
} 

ImageLoader.java

import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.UnsupportedEncodingException; 
import java.net.URLEncoder; 
import java.util.Collections; 
import java.util.Map; 
import java.util.WeakHashMap; 
import java.util.concurrent.ExecutorService; 
import java.util.concurrent.Executors; 
import android.app.Activity; 
import android.content.Context; 
import android.graphics.Bitmap; 
import android.graphics.BitmapFactory; 
import android.graphics.drawable.BitmapDrawable; 
import android.widget.ImageView; 
 
public class ImageLoader { 
 
  private MemoryCache memoryCache = new MemoryCache(); 
  private FileCache fileCache; 
  private Map<ImageView, String> imageViews = Collections 
      .synchronizedMap(new WeakHashMap<ImageView, String>()); 
  private ExecutorService executorService; 
  private boolean isSrc; 
 
  /**
  * @param context
  *      上下文对象
  * @param flag
  *      true为source资源，false为background资源
  */ 
  public ImageLoader(Context context, boolean flag) { 
    fileCache = new FileCache(context); 
    executorService = Executors.newFixedThreadPool(5); 
    isSrc = flag; 
  } 
 
  final int stub_id = R.drawable.ic_launcher; 
 
  public void DisplayImage(String url, ImageView imageView) { 
    String u1 = url.substring(0, url.lastIndexOf("/") + 1); 
    String u2 = url.substring(url.lastIndexOf("/") + 1); 
    try { 
      u2 = URLEncoder.encode(u2, "UTF-8"); 
    } catch (UnsupportedEncodingException e) { 
      e.printStackTrace(); 
    } 
    url = u1 + u2; 
    imageViews.put(imageView, url); 
    Bitmap bitmap = memoryCache.get(url); 
    if (bitmap != null) { 
      if (isSrc) 
        imageView.setImageBitmap(bitmap); 
      else 
        imageView.setBackgroundDrawable(new BitmapDrawable(bitmap)); 
    } else { 
      queuePhoto(url, imageView); 
      if (isSrc) 
        imageView.setImageResource(stub_id); 
      else 
        imageView.setBackgroundResource(stub_id); 
    } 
  } 
 
  private void queuePhoto(String url, ImageView imageView) { 
    PhotoToLoad p = new PhotoToLoad(url, imageView); 
    executorService.submit(new PhotosLoader(p)); 
  } 
 
  private Bitmap getBitmap(String url) { 
    try { 
      File f = fileCache.getFile(url); 
      // 从sd卡 
      Bitmap b = onDecodeFile(f); 
      if (b != null) 
        return b; 
      // 从网络 
      Bitmap bitmap = null; 
      System.out.println("ImageLoader-->download"); 
      HttpUtil.CopyStream(url, f); 
      bitmap = onDecodeFile(f); 
 
      return bitmap; 
    } catch (Exception ex) { 
      ex.printStackTrace(); 
      return null; 
    } 
  } 
 
  public Bitmap onDecodeFile(File f) { 
    try { 
      return BitmapFactory.decodeStream(new FileInputStream(f)); 
    } catch (FileNotFoundException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
    } 
    return null; 
  } 
 
  /**
  * 解码图像用来减少内存消耗
  * 
  * @param f
  * @return
  */ 
  public Bitmap decodeFile(File f) { 
    try { 
      // 解码图像大小 
      BitmapFactory.Options o = new BitmapFactory.Options(); 
      o.inJustDecodeBounds = true; 
      BitmapFactory.decodeStream(new FileInputStream(f), null, o); 
      // 找到正确的刻度值，它应该是2的幂。 
      final int REQUIRED_SIZE = 70; 
      int width_tmp = o.outWidth, height_tmp = o.outHeight; 
      int scale = 1; 
      while (true) { 
        if (width_tmp / 2 < REQUIRED_SIZE || height_tmp / 2 < REQUIRED_SIZE) 
          break; 
        width_tmp /= 2; 
        height_tmp /= 2; 
        scale *= 2; 
      } 
      BitmapFactory.Options o2 = new BitmapFactory.Options(); 
      o2.inSampleSize = scale; 
      return BitmapFactory.decodeStream(new FileInputStream(f), null, o2); 
    } catch (FileNotFoundException e) { 
    } 
    return null; 
  } 
 
  /**
  * 任务队列
  * 
  * @author Scorpio.Liu
  * 
  */ 
  private class PhotoToLoad { 
    public String url; 
    public ImageView imageView; 
 
    public PhotoToLoad(String u, ImageView i) { 
      url = u; 
      imageView = i; 
    } 
  } 
 
  class PhotosLoader implements Runnable { 
    PhotoToLoad photoToLoad; 
 
    PhotosLoader(PhotoToLoad photoToLoad) { 
      this.photoToLoad = photoToLoad; 
    } 
 
    @Override 
    public void run() { 
      if (imageViewReused(photoToLoad)) 
        return; 
      Bitmap bmp = getBitmap(photoToLoad.url); 
      memoryCache.put(photoToLoad.url, bmp); 
      if (imageViewReused(photoToLoad)) 
        return; 
      BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad); 
      Activity a = (Activity) photoToLoad.imageView.getContext(); 
      a.runOnUiThread(bd); 
    } 
  } 
 
  boolean imageViewReused(PhotoToLoad photoToLoad) { 
    String tag = imageViews.get(photoToLoad.imageView); 
    if (tag == null || !tag.equals(photoToLoad.url)) 
      return true; 
    return false; 
  } 
 
  /**
  * 显示位图在UI线程
  * 
  * @author Scorpio.Liu
  * 
  */ 
  class BitmapDisplayer implements Runnable { 
    Bitmap bitmap; 
    PhotoToLoad photoToLoad; 
 
    public BitmapDisplayer(Bitmap b, PhotoToLoad p) { 
      bitmap = b; 
      photoToLoad = p; 
    } 
 
    public void run() { 
      if (imageViewReused(photoToLoad)) 
        return; 
      if (bitmap != null) { 
        if (isSrc) 
          photoToLoad.imageView.setImageBitmap(bitmap); 
        else 
          photoToLoad.imageView.setBackgroundDrawable(new BitmapDrawable(bitmap)); 
      } else { 
        if (isSrc) 
          photoToLoad.imageView.setImageResource(stub_id); 
        else 
          photoToLoad.imageView.setBackgroundResource(stub_id); 
      } 
    } 
  } 
 
  public void clearCache() { 
    memoryCache.clear(); 
    fileCache.clear(); 
  } 
 
} 
								 
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