项目中用到的，要求一次下载30张图片。开始时使用谷歌bitmap fun中提供的ImageFetcher来下载，但是发现一个蛋疼无比现象，图片总是莫名其妙的少几张。
排除了图片地址存在无效链接外，怀疑是并发下载线程个数太多，线程池满了以后，使用抛弃策略将以前的下载线程抛弃了。
求人不如求己，自己写一个吧。
在这里使用线程池，支持并发下载。线程池可以自己选择，使用 newSingleThreadExecutor，newFixedThreadPool，newCachedThreadPool中的任意一种。使用 时，自己实现监听器，当监听下载个数与url集合的个数相同时，会回调监听器的onSuccess()方法。
源码如下，希望大家指正
代码语言：javascript复制import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
import android.util.Log;
/**
* 批量图片下载类 无需与界面交互的下载类
*
* @Description:
*
* @author- liubing
* @create- 2013-5 -6
* @modify by:
* @modify- time
*/
public class DownloadService {
private static String TAG = "DownloadService" ;
public static final int IO_BUFFER_SIZE = 8 * 1024;
private static final String CACHE_FILENAME_PREFIX = "cache_";
private static ExecutorService SINGLE_TASK_EXECUTOR = null;
private static ExecutorService LIMITED_TASK_EXECUTOR = null;
private static final ExecutorService FULL_TASK_EXECUTOR = null;
private static final ExecutorService DEFAULT_TASK_EXECUTOR ;
private static Object lock = new Object();
static {
// SINGLE_TASK_EXECUTOR = (ExecutorService)
// Executors.newSingleThreadExecutor();
LIMITED_TASK_EXECUTOR = (ExecutorService) Executors
. newFixedThreadPool(1);
// FULL_TASK_EXECUTOR = (ExecutorService)
// Executors.newCachedThreadPool();
DEFAULT_TASK_EXECUTOR = LIMITED_TASK_EXECUTOR ;
};
// 下载状态监听，提供回调
DownloadStateListener listener;
// 下载目录
private String downloadPath;
// 下载链接集合
private List<String> listURL;
// 下载个数
private int size = 0;
// 下载完成回调接口
public interface DownloadStateListener {
public void onFinish();
public void onFailed();
}
public DownloadService(String downloadPath, List<String> listURL,
DownloadStateListener listener) {
this.downloadPath = downloadPath;
this.listURL = listURL;
this.listener = listener;
}
/**
* 暂未提供设置
*/
public void setDefaultExecutor() {
}
/**
* 开始下载
*/
public void startDownload() {
// 首先检测path是否存在
File downloadDirectory = new File(downloadPath );
if (!downloadDirectory.exists()) {
downloadDirectory.mkdirs();
}
for (final String url : listURL) {
//捕获线程池拒绝执行异常
try {
// 线程放入线程池
DEFAULT_TASK_EXECUTOR.execute(new Runnable() {
@Override
public void run() {
downloadBitmap(url);
}
});
} catch (RejectedExecutionException e) {
e.printStackTrace();
Log. e(TAG, "thread pool rejected error");
listener.onFailed();
} catch (Exception e) {
e.printStackTrace();
listener.onFailed();
}
}
}
/**
* 下载图片
*
* @param urlString
* @return
*/
private File downloadBitmap(String urlString) {
String fileName = urlString;
// 图片命名方式
final File cacheFile = new File(createFilePath(new File(
downloadPath), fileName));
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
final InputStream in = new BufferedInputStream(
urlConnection.getInputStream(), IO_BUFFER_SIZE);
out = new BufferedOutputStream(new FileOutputStream(cacheFile),
IO_BUFFER_SIZE);
int b;
while ((b = in.read()) != -1) {
out.write(b);
}
// 每下载成功一个，统计一下图片个数
statDownloadNum();
return cacheFile;
} catch (final IOException e) {
// 有一个下载失败，则表示批量下载没有成功
Log. e(TAG, "download " urlString " error");
listener.onFailed();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (out != null ) {
try {
out.close();
} catch (final IOException e) {
Log. e(TAG, "Error in downloadBitmap - " e);
}
}
}
return null ;
}
/**
* Creates a constant cache file path given a target cache directory and an
* image key.
*
* @param cacheDir
* @param key
* @return
*/
public static String createFilePath(File cacheDir, String key) {
try {
// Use URLEncoder to ensure we have a valid filename, a tad hacky
// but it will do for
// this example
return cacheDir.getAbsolutePath() File.separator CACHE_FILENAME_PREFIX
URLEncoder.encode(key.replace("*", ""), "UTF-8" );
} catch (final UnsupportedEncodingException e) {
Log. e(TAG, "createFilePath - " e);
}
return null ;
}
/**
* 统计下载个数
*/
private void statDownloadNum() {
synchronized (lock ) {
size ;
if (size == listURL .size()) {
Log. d(TAG, "download finished total " size);
// 释放资源
DEFAULT_TASK_EXECUTOR.shutdownNow();
// 如果下载成功的个数与列表中 url个数一致，说明下载成功
listener.onFinish(); // 下载成功回调
}
}
}
} 使用方法如下：
代码语言：javascript复制new DownloadService( "/mnt/sdcard/test", listUrl, new DownloadStateListener() {
@Override
public void onFinish() {
//图片下载成功后，实现您的代码
}
@Override
public void onFailed() {
//图片下载成功后，实现您的代码
}
}).startDownload();
