Android实现网络多线程文件下载

实现原理

(1)首先获得下载文件的长度，然后设置本地文件的长度。

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示：

（网上找的图）

 例如10M大小，使用3个线程来下载，

线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M
下载开始位置：线程id*每条线程下载的数据长度 = ?
下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用数据库，不再加了，网上有很多成熟的项目可以直接用。

实例

MainApp：

package com.amos.app;import java.io.File;import java.io.IOException;import java.net.MalformedURLException;import java.net.URL;import java.net.URLConnection;import com.amos.download.R;import android.annotation.SuppressLint;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.os.Handler;import android.os.Message;import android.util.Log;import android.view.View;import android.view.View.OnClickListener;import android.widget.ProgressBar;import android.widget.TextView;import android.widget.Toast;/** * @author yangxiaolong * @2014-5-6 */public class MainApp extends Activity implements OnClickListener {private static final String TAG = MainApp.class.getSimpleName();/** 显示下载进度TextView */private TextView mMessageView;/** 显示下载进度ProgressBar */private ProgressBar mProgressbar;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.progress_activity);findViewById(R.id.download_btn).setOnClickListener(this);mMessageView = (TextView) findViewById(R.id.download_message);mProgressbar = (ProgressBar) findViewById(R.id.download_progress);}@Overridepublic void onClick(View v) {if (v.getId() == R.id.download_btn) {doDownload();}}/** * 使用Handler更新UI界面信息 */@SuppressLint("HandlerLeak")Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {mProgressbar.setProgress(msg.getData().getInt("size"));float temp = (float) mProgressbar.getProgress()/ (float) mProgressbar.getMax();int progress = (int) (temp * 100);if (progress == 100) {Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH_LONG).show();}mMessageView.setText("下载进度:" + progress + " %");}};/** * 下载准备工作，获取SD卡路径、开启线程 */private void doDownload() {// 获取SD卡路径String path = Environment.getExternalStorageDirectory()+ "/amosdownload/";File file = new File(path);// 如果SD卡目录不存在创建if (!file.exists()) {file.mkdir();}// 设置progressBar初始化mProgressbar.setProgress(0);// 简单起见，我先把URL和文件名称写死，其实这些都可以通过HttpHeader获取到String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk";String fileName = "baidu_16785426.apk";int threadNum = 5;String filepath = path + fileName;Log.d(TAG, "download file  path:" + filepath);downloadTask task = new downloadTask(downloadUrl, threadNum, filepath);task.start();}/** * 多线程文件下载 *  * @author yangxiaolong * @2014-8-7 */class downloadTask extends Thread {private String downloadUrl;// 下载链接地址private int threadNum;// 开启的线程数private String filePath;// 保存文件路径地址private int blockSize;// 每一个线程的下载量public downloadTask(String downloadUrl, int threadNum, String fileptah) {this.downloadUrl = downloadUrl;this.threadNum = threadNum;this.filePath = fileptah;}@Overridepublic void run() {FileDownloadThread[] threads = new FileDownloadThread[threadNum];try {URL url = new URL(downloadUrl);Log.d(TAG, "download file http path:" + downloadUrl);URLConnection conn = url.openConnection();// 读取下载文件总大小int fileSize = conn.getContentLength();if (fileSize <= 0) {System.out.println("读取文件失败");return;}// 设置ProgressBar最大的长度为文件SizemProgressbar.setMax(fileSize);// 计算每条线程下载的数据长度blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum: fileSize / threadNum + 1;Log.d(TAG, "fileSize:" + fileSize + "  blockSize:");File file = new File(filePath);for (int i = 0; i < threads.length; i++) {// 启动线程，分别下载每个线程需要下载的部分threads[i] = new FileDownloadThread(url, file, blockSize,(i + 1));threads[i].setName("Thread:" + i);threads[i].start();}boolean isfinished = false;int downloadedAllSize = 0;while (!isfinished) {isfinished = true;// 当前所有线程下载总量downloadedAllSize = 0;for (int i = 0; i < threads.length; i++) {downloadedAllSize += threads[i].getDownloadLength();if (!threads[i].isCompleted()) {isfinished = false;}}// 通知handler去更新视图组件Message msg = new Message();msg.getData().putInt("size", downloadedAllSize);mHandler.sendMessage(msg);// Log.d(TAG, "current downloadSize:" + downloadedAllSize);Thread.sleep(1000);// 休息1秒后再读取下载进度}Log.d(TAG, " all of downloadSize:" + downloadedAllSize);} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} catch (InterruptedException e) {e.printStackTrace();}}}}

FileDownloadThread:

package com.amos.app;import java.io.BufferedInputStream;import java.io.File;import java.io.IOException;import java.io.RandomAccessFile;import java.net.URL;import java.net.URLConnection;import android.util.Log;/** * 文件下载类 *  * @author yangxiaolong * @2014-5-6 */public class FileDownloadThread extends Thread {private static final String TAG = FileDownloadThread.class.getSimpleName();/** 当前下载是否完成 */private boolean isCompleted = false;/** 当前下载文件长度 */private int downloadLength = 0;/** 文件保存路径 */private File file;/** 文件下载路径 */private URL downloadUrl;/** 当前下载线程ID */private int threadId;/** 线程下载数据长度 */private int blockSize;/** *  * @param url:文件下载地址 * @param file:文件保存路径 * @param blocksize:下载数据长度 * @param threadId:线程ID */public FileDownloadThread(URL downloadUrl, File file, int blocksize,int threadId) {this.downloadUrl = downloadUrl;this.file = file;this.threadId = threadId;this.blockSize = blocksize;}@Overridepublic void run() {BufferedInputStream bis = null;RandomAccessFile raf = null;try {URLConnection conn = downloadUrl.openConnection();conn.setAllowUserInteraction(true);int startPos = blockSize * (threadId - 1);//开始位置int endPos = blockSize * threadId - 1;//结束位置//设置当前线程下载的起点、终点conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);System.out.println(Thread.currentThread().getName() + "  bytes="+ startPos + "-" + endPos);byte[] buffer = new byte[1024];bis = new BufferedInputStream(conn.getInputStream());raf = new RandomAccessFile(file, "rwd");raf.seek(startPos);int len;while ((len = bis.read(buffer, 0, 1024)) != -1) {raf.write(buffer, 0, len);downloadLength += len;}isCompleted = true;Log.d(TAG, "current thread task has finished,all size:"+ downloadLength);} catch (IOException e) {e.printStackTrace();} finally {if (bis != null) {try {bis.close();} catch (IOException e) {e.printStackTrace();}}if (raf != null) {try {raf.close();} catch (IOException e) {e.printStackTrace();}}}}/** * 线程文件是否下载完毕 */public boolean isCompleted() {return isCompleted;}/** * 线程下载文件长度 */public int getDownloadLength() {return downloadLength;}}

效果图：

Log控制台：

可以看到文件总大小、我们创建的5个线程每个负责下载的区间

SD卡：

断点续传

这个用到了数据存储保存当前每个线程下载文件的长度，等下一次再下载时读取，网上有成熟的案例，就不再造轮子了，资源里我打包了自己的项目和带断点续传的项目（别人的），大家可以下载下来直接用，全部免费：

http://download.csdn.net/detail/mad1989/7727133