网络下载图片并显示代码片段

一、DowdloadImage

package org.app.netmusic.tool;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Collections;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.app.netmusic.tool.HttpTool.FileCache;
import org.app.netmusic.tool.HttpTool.MemoryCache;
import org.app.netmusic.tool.HttpTool.Utils;
import org.app.qqmusicplayer.R;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.widget.ImageView;

public class DowdloadImage {
       MemoryCache memoryCache=new MemoryCache();   
        FileCache fileCache;   
        private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());   
        ExecutorService executorService;    
        
        public DowdloadImage(Context context){   
            fileCache=new FileCache(context);   
            executorService=Executors.newFixedThreadPool(5);   
        }   
        
        final int stub_id = R.drawable.music;
        public void DisplayImage(String url, ImageView imageView)   
        {   
            imageViews.put(imageView, url);   
            Bitmap bitmap=memoryCache.get(url);   
            if(bitmap!=null)   
                imageView.setImageBitmap(bitmap);   
            else  
            {   
                queuePhoto(url, imageView);   
                imageView.setImageResource(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)   
        {   
            File f=fileCache.getFile(url);   
        
            //从sd卡  
            Bitmap b = decodeFile(f);   
            if(b!=null)   
                return b;   
        
            //从网络  
            try {   
                Bitmap bitmap=null;   
                URL imageUrl = new URL(url);   
                HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();   
                conn.setConnectTimeout(30000);   
                conn.setReadTimeout(30000);   
                conn.setInstanceFollowRedirects(true);   
                InputStream is=conn.getInputStream();   
                OutputStream os = new FileOutputStream(f);   
                Utils.CopyStream(is, os);   
                os.close();   
                bitmap = decodeFile(f);   
                return bitmap;   
            } catch (Exception ex){   
               ex.printStackTrace();   
               return null;   
            }   
        }   
        
        //解码图像用来减少内存消耗  
        private 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  
        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;   
        }   
        
        //用于显示位图在UI线程  
        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)   
                    photoToLoad.imageView.setImageBitmap(bitmap);   
                else  
                    photoToLoad.imageView.setImageResource(stub_id);   
            }   
        }   
        
        public void clearCache() {   
            memoryCache.clear();   
            fileCache.clear();   
        }
}

二、HttpTool

package com.ct.app.netmusic;

import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;
import java.lang.ref.SoftReference;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import android.content.Context;
import android.graphics.Bitmap;

public class HttpTool {
    public static 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();  
        }  
    }
    public static class FileCache{
         private File cacheDir;  
         public FileCache(Context context){  
                //找一个用来缓存图片的路径  
                if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))  
                    cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"musicLists");  
                else  
                    cacheDir=context.getCacheDir();  
                if(!cacheDir.exists())  
                    cacheDir.mkdirs();  
            }  
              
            public File getFile(String url){  
                  
                String filename=String.valueOf(url.hashCode());  
                File f = new File(cacheDir, filename);  
                return f;  
                  
            }  
              
            public void clear(){  
                File[] files=cacheDir.listFiles();  
                if(files==null)  
                    return;  
                for(File f:files)  
                    f.delete();  
            }  
          
    }
    public static class Utils{
        public static void CopyStream(InputStream is, OutputStream os)  
        {  
            final int buffer_size=1024;  
            try  
            {  
                byte[] bytes=new byte[buffer_size];  
                for(;;)  
                {  
                  int count=is.read(bytes, 0, buffer_size);  
                  if(count==-1)  
                      break;  
                  os.write(bytes, 0, count);  
                 
                }  
                is.close();  
                os.close();  
            }  
            catch(Exception ex){}  
        }  
    }
}

三、使用

imageLoader.DisplayImage(song.get(MusicOnlineActivity.KEY_THUMB_URL), thumb_image);