android下载网络图片并缓存

异步下载网络图片，并提供是否缓存至内存或外部文件的功能

异步加载类AsyncImageLoader

    public void downloadImage(final String url, final ImageCallback callback);

    public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback);

    public void setCache2File(boolean flag);

    public void setCachedDir(String dir);

图片下载和缓存实现类LoaderImpl

package com.imagecache;


import java.lang.ref.SoftReference;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


import android.content.Context;
import android.graphics.Bitmap;
import android.os.Handler;
import android.util.Log;


public class AsyncImageLoader {
//保存正在下载的图片URL集合，避免重复下载用
private static HashSet<String> sDownloadingSet;
//软引用内存缓存
private static Map<String,SoftReference<Bitmap>> sImageCache; 
//图片三种获取方式管理者，网络URL获取、内存缓存获取、外部文件缓存获取
private static LoaderImpl impl;
//线程池相关
private static ExecutorService sExecutorService;

//通知UI线程图片获取ok时使用
private Handler handler; 


/**
* 异步加载图片完毕的回调接口
*/
public interface ImageCallback{
/**
* 回调函数
* @param bitmap: may be null!
* @param imageUrl 
*/
public void onImageLoaded(Bitmap bitmap, String imageUrl);
}

static{
sDownloadingSet = new HashSet<String>();
sImageCache = new HashMap<String,SoftReference<Bitmap>>();
impl = new LoaderImpl(sImageCache);
}


public AsyncImageLoader(Context context){
handler = new Handler();
startThreadPoolIfNecessary();

String defaultDir = context.getCacheDir().getAbsolutePath();
setCachedDir(defaultDir);
}

/**
* 是否缓存图片至/data/data/package/cache/目录
* 默认不缓存
*/
public void setCache2File(boolean flag){
impl.setCache2File(flag);
}

/**
* 设置缓存路径，setCache2File(true)时有效
*/
public void setCachedDir(String dir){
impl.setCachedDir(dir);
}


/**开启线程池*/
public static void startThreadPoolIfNecessary(){
if(sExecutorService == null || sExecutorService.isShutdown() || sExecutorService.isTerminated()){
sExecutorService = Executors.newFixedThreadPool(3);
//sExecutorService = Executors.newSingleThreadExecutor();
}
}

/**
* 异步下载图片，并缓存到memory中
* @param url
* @param callbacksee ImageCallback interface
*/
public void downloadImage(final String url, final ImageCallback callback){
downloadImage(url, true, callback);
}

/**
* 
* @param url
* @param cache2Memory 是否缓存至memory中
* @param callback
*/
public void downloadImage(final String url, final boolean cache2Memory, final ImageCallback callback){
if(sDownloadingSet.contains(url)){
Log.i("AsyncImageLoader", "###该图片正在下载，不能重复下载！");
return;
}

Bitmap bitmap = impl.getBitmapFromMemory(url);
if(bitmap != null){
if(callback != null){
callback.onImageLoaded(bitmap, url);
}
}else{
//从网络端下载图片
sDownloadingSet.add(url);
sExecutorService.submit(new Runnable(){
@Override
public void run() {
final Bitmap bitmap = impl.getBitmapFromUrl(url, cache2Memory);
handler.post(new Runnable(){
@Override
public void run(){
if(callback != null)
callback.onImageLoaded(bitmap, url);
sDownloadingSet.remove(url);
}
});
}
});
}
}

/**
* 预加载下一张图片，缓存至memory中
* @param url 
*/
public void preLoadNextImage(final String url){
//将callback置为空，只将bitmap缓存到memory即可。
downloadImage(url, null);
}

}

package com.imagecache;


import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.lang.ref.SoftReference;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Map;


import android.graphics.Bitmap;
import android.graphics.BitmapFactory;


/**
 * 
 * @author Administrator
 * @desc 异步加载图片管理器
 *
 */
public class LoaderImpl {
//内存中的软应用缓存
private Map<String, SoftReference<Bitmap>> imageCache;

//是否缓存图片至本地文件
private boolean cache2FileFlag = false;

//缓存目录,默认是/data/data/package/cache/目录
private String cachedDir;

public LoaderImpl(Map<String, SoftReference<Bitmap>> imageCache){
this.imageCache = imageCache;
}

/**
* 是否缓存图片至外部文件
* @param flag 
*/
public void setCache2File(boolean flag){
cache2FileFlag = flag;
}

/**
* 设置缓存图片到外部文件的路径
* @param cacheDir
*/
public void setCachedDir(String cacheDir){
this.cachedDir = cacheDir;
}

/**
* 从网络端下载图片
* @param url 网络图片的URL地址
* @param cache2Memory 是否缓存(缓存在内存中)
* @return bitmap 图片bitmap结构
* 
*/
public Bitmap getBitmapFromUrl(String url, boolean cache2Memory){
Bitmap bitmap = null;
try{
URL u = new URL(url);
HttpURLConnection conn = (HttpURLConnection)u.openConnection();  
InputStream is = conn.getInputStream();
bitmap = BitmapFactory.decodeStream(is);

if(cache2Memory){
//1.缓存bitmap至内存软引用中
imageCache.put(url, new SoftReference<Bitmap>(bitmap));
if(cache2FileFlag){
//2.缓存bitmap至/data/data/packageName/cache/文件夹中
String fileName = getMD5Str(url);
String filePath = this.cachedDir + "/" +fileName;
FileOutputStream fos = new FileOutputStream(filePath);
bitmap.compress(Bitmap.CompressFormat.PNG, 100, fos);
}
}

is.close();
conn.disconnect();
return bitmap;
}catch(IOException e){
e.printStackTrace();
return null;
}
}

/**
* 从内存缓存中获取bitmap
* @param url
* @return bitmap or null.
*/
public Bitmap getBitmapFromMemory(String url){
Bitmap bitmap = null;
if(imageCache.containsKey(url)){
synchronized(imageCache){
SoftReference<Bitmap> bitmapRef = imageCache.get(url);
if(bitmapRef != null){
bitmap = bitmapRef.get();
return bitmap;
}
}
}
//从外部缓存文件读取
if(cache2FileFlag){
bitmap = getBitmapFromFile(url);
if(bitmap != null)
imageCache.put(url, new SoftReference<Bitmap>(bitmap));
}

return bitmap;
}

/**
* 从外部文件缓存中获取bitmap
* @param url
* @return
*/
private Bitmap getBitmapFromFile(String url){
Bitmap bitmap = null;
String fileName = getMD5Str(url);
if(fileName == null)
return null;

String filePath = cachedDir + "/" + fileName;

try {
FileInputStream fis = new FileInputStream(filePath);
bitmap = BitmapFactory.decodeStream(fis);
} catch (FileNotFoundException e) {
e.printStackTrace();
bitmap = null;
}
return bitmap;
}


/**  
     * MD5 加密  
     */   
    private static String getMD5Str(String str) {   
        MessageDigest messageDigest = null;   
        try {   
            messageDigest = MessageDigest.getInstance("MD5");   
            messageDigest.reset();   
            messageDigest.update(str.getBytes("UTF-8"));   
        } catch (NoSuchAlgorithmException e) {   
            System.out.println("NoSuchAlgorithmException caught!");   
            return null;
        } catch (UnsupportedEncodingException e) {   
            e.printStackTrace();
            return null;
        }   
   
        byte[] byteArray = messageDigest.digest();   
        StringBuffer md5StrBuff = new StringBuffer();   
        for (int i = 0; i < byteArray.length; i++) {               
            if (Integer.toHexString(0xFF & byteArray[i]).length() == 1)   
                md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));   
            else   
                md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));   
        }   
   
        return md5StrBuff.toString();   
    }  


/**  
     * MD5 加密  
    private static String getMD5Str(Object...objects){
    StringBuilder stringBuilder=new StringBuilder();
    for (Object object : objects) {
stringBuilder.append(object.toString());
}
    return getMD5Str(stringBuilder.toString());
    }*/ 
}

package com.imagecache;


import android.app.Activity;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.widget.ImageView;


public class MainActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        final ImageView iv = (ImageView)findViewById(R.id.iv);
        //网络图片地址
        String imgUrl = "http://...";
        
        //for test
        AsyncImageLoader loader = new AsyncImageLoader(getApplicationContext());
        
        //将图片缓存至外部文件中
        loader.setCache2File(true); //false
        //设置外部缓存文件夹
        loader.setCachedDir(this.getCacheDir().getAbsolutePath());
        
        //下载图片，第二个参数是否缓存至内存中
        loader.downloadImage(imgUrl, true/*false*/, new AsyncImageLoader.ImageCallback() {
@Override
public void onImageLoaded(Bitmap bitmap, String imageUrl) {
if(bitmap != null){
iv.setImageBitmap(bitmap);
}else{
//下载失败，设置默认图片
}
}
});
    }
    
}

添加网络权限

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