Android 多线程网络下载图片

最近项目中碰到了多线程下载图片的问题，我自己写了一个工具类 ImageLoader， 该工具类支持图片缓存：有SDCARD缓存，内存缓存等，支持多线程下载，其具体实现思路为：

1、实现一个线程池 ExecutorService，将下载多线程的任务添加到该线程池中，可以定义线程池的大小

2、下载到图片成功之后，如何通知UI线程去更新UI

3、图片的缓存处理等。

其核心代码如下：

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 android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.text.TextUtils;
import android.widget.ImageView;
import com.giant.lib.utils.GiantLog;
import giant.activity.R;

public class ImageLoader {

final int stub_id = R.drawable.default_user_ico;
MemoryCache memoryCache = new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews = Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
private static final String TAG = "ImageLoader";

public ImageLoader(Context context){
fileCache = new FileCache(context);
executorService = Executors.newFixedThreadPool(5);
}

/**
* 显示图片需要默认图片
* @param url
* @param imageView
*/
public void DisplayImage(String url, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap = memoryCache.get(url);

if(TextUtils.isEmpty(url)){
imageView.setImageResource(R.drawable.default_user_ico);
}

//        Bitmap bitmap = null;
if(bitmap!= null)   { //先加载内存中的缓存
imageView.setImageBitmap(bitmap);
GiantLog.d(TAG, "load image data form memory");
}

else
{
queuePhoto(url,imageView);
imageView.setImageResource(stub_id);
}
}

/**
* 显示图片不需要默认图片
* @param url
* @param imageView
*/
public void DisplayImageWithNodefault(String url, ImageView imageView)
{
imageViews.put(imageView, url);
Bitmap bitmap = memoryCache.get(url);

//        Bitmap bitmap = null;
if(bitmap!= null)   { //先加载内存中的缓存
imageView.setImageBitmap(bitmap);
GiantLog.d(TAG, "load image data form memory");
}

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)  {
GiantLog.d(TAG,"load image from sdcard");
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);
GiantLog.d(TAG,"load image from network" );

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 options = new BitmapFactory.Options();
options.inSampleSize = 1;
return BitmapFactory.decodeStream(new FileInputStream(f), null, options);
} catch (FileNotFoundException e) {
GiantLog.d(TAG,"exception:" + e);
}
return null;
}

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 bitmapDisplayer = new BitmapDisplayer(bmp, photoToLoad);
Activity activity =(Activity)photoToLoad.imageView.getContext();
activity.runOnUiThread(bitmapDisplayer);
}
}

boolean imageViewReused(PhotoToLoad photoToLoad){
String tag = imageViews.get(photoToLoad.imageView);
return tag == null || !tag.equals(photoToLoad.url);
}

//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);
}
}

/**
* 清除所有的缓存(包括内存和SD卡)
*/
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}

/**
* 只清除内存中的缓存
*/
public void clearMemoryCache(){
memoryCache.clear();
}

}

具体使用很简单：

ImageLoader imageLoader = new ImageLoader(Activity.this) ;

imageLoader.DisplayImageWithNodefault(pic_url,imageVew,false); //不需要显示默认图片

全部源码下载链接：

http://download.csdn.net/detail/nanzhiwen666/5955391