封装一个工具类，搞定图片批量下载

   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

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：

 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();

  原文链接：http://www.67tgb.com/?p=590

  转载注明：望月听涛