使用HttpURLConnection实现多线程下载

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HttpURLConnection继承了URLConnection，因此也可用于向指定网站发送GET请求、POST请求，而且它在URLConnection基础上提供了如下便捷方法：

实现多线程下载的步骤：

下面用一个示例来示范使用HttpURLConnection实现多线程下载。此代码来源疯狂讲义一书，该代码主要思路：在Activity中点击按钮,调用DownUtil的download()方法，在download()中启动四个线程去下载资源，每个线程负责下载自己的那部分资源，代码如下：

Activity：

package com.home.activity;import java.util.Timer;
import java.util.TimerTask;import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;import com.home.multithreaddown.R;
import com.home.util.DownUtil;public class MultiThreadDownActivity extends Activity {private EditText urlText;private EditText targetText;private Button downBtn;private ProgressBar bar;private DownUtil downUtil;private int mDownStatus;private Handler handler;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);// 获取界面中控件targetText = (EditText) findViewById(R.id.main_et_name);urlText = (EditText) findViewById(R.id.main_et_url);downBtn = (Button) findViewById(R.id.main_btn_download);bar = (ProgressBar) findViewById(R.id.main_progressBar);// 创建一个Handler对象handler = new Handler() {public void handleMessage(Message msg) {if (msg.what == 0x123) {bar.setProgress(mDownStatus);}}};downBtn.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// 初始化DownUtil对象downUtil = new DownUtil(urlText.getText().toString(),targetText.getText().toString(), 4);try {// 开始下载downUtil.download();} catch (Exception e) {e.printStackTrace();}// 定义每秒调度获取一次系统的完成进度final Timer timer = new Timer();timer.schedule(new TimerTask() {public void run() {// 获取下载任务的完成比率double completeRate = downUtil.getCompleteRate();mDownStatus = (int) (completeRate * 100);// 发送消息通知界面更新进度条handler.sendEmptyMessage(0x123);// 下载完成后取消任务调度if (mDownStatus >= 100) {timer.cancel();}}}, 0, 100);}});}}

下载的工具类（DownUtil）：

package com.home.util;import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;public class DownUtil {// 定义下载资源的路径private String path;// 指定所下载的文件的保存位置private String targetFile;// 定义需要使用多少线程下载资源private int threadNum;// 定义下载的文件的总大小private int fileSize;// 定义下载的线程对象private DownloadThread[] threads;public DownUtil(String path, String targetFile, int threadNum) {this.path = path;this.threadNum = threadNum;// 初始化threads数组threads = new DownloadThread[threadNum];this.targetFile = targetFile;}public void download() throws Exception {URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif,image/jpeg,image/pjpeg,application/x-shockwaveflash,application/x-ms-xbap,application/xaml+xml,application/vnd.ms-xpsdocument,application/x-ms-application,application/vnd.ms-excel,application/vnd.ms-powerpoint,application/msword,*/*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");conn.setRequestProperty("User-Agent","Mozilla/4.0(compatible;MSIE7.0;Windows NT 5.2;Trident/4.0;.NET CLR 1.1.4322;.NET CLR 2.0.50727;.NET CLR 3.0.04506.30;.NET CLR 3.0.4506.2152;.NET CLR 3.5.30729)");conn.setRequestProperty("Connection", "Keep-Alive");// 得到文件大小fileSize = conn.getContentLength();conn.disconnect();int currentPartSize = fileSize / threadNum + 1;RandomAccessFile file = new RandomAccessFile(targetFile, "rw");// 设置本地文件的大小file.setLength(fileSize);file.close();for (int i = 0; i < threadNum; i++) {// 计算每条线程的下载的开始位置int startPos = i * currentPartSize;// 每个线程使用一个RandomAccessFile进行下载RandomAccessFile currentPart = new RandomAccessFile(targetFile,"rw");// 定位该线程的下载位置currentPart.seek(startPos);// 创建下载线程threads[i] = new DownloadThread(startPos, currentPartSize,currentPart);// 启动下载线程threads[i].start();}}/*** 获取下载完成的百分比* * @return*/public double getCompleteRate() {// 统计多条线程已经下载的总大小int sumSize = 0;for (int i = 0; i < threadNum; i++) {sumSize += threads[i].length;}// 返回已经完成的百分比return sumSize * 1.0 / fileSize;}private class DownloadThread extends Thread {// 当前线程的下载位置private int startPos;// 定义当前线程负责下载的文件大小private int currentPartSize;// 当前线程需要下载的文件块private RandomAccessFile currentPart;// 定义该线程已下载的字节数private int length = 0;public DownloadThread(int startPos, int currentPartSize,RandomAccessFile currentPart) {this.startPos = startPos;this.currentPartSize = currentPartSize;this.currentPart = currentPart;}public void run() {try {URL url = new URL(path);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setConnectTimeout(5 * 1000);conn.setRequestMethod("GET");conn.setRequestProperty("Accept","image/gif,image/jpeg,image/pjpeg,application/x-shockwaveflash,application/x-ms-xbap,application/xaml+xml,application/vnd.ms-xpsdocument,application/x-ms-application,application/vnd.ms-excel,application/vnd.ms-powerpoint,application/msword,*/*");conn.setRequestProperty("Accept-Language", "zh-CN");conn.setRequestProperty("Charset", "UTF-8");InputStream is = conn.getInputStream();// 跳过startPos个字符，表明该线程只下载自己负责那部分文件is.skip(startPos);byte[] by = new byte[1024];int hasRead = 0;// 读取网络数据，并写入本地文件while (length < currentPartSize&& (hasRead = is.read(by)) != -1) {currentPart.write(by, 0, hasRead);// 累计该线程下载的总大小length += hasRead;}currentPart.close();is.close();} catch (Exception e) {e.printStackTrace();}}}
}

Activity布局XML：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal" ><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="输入url:" /><EditTextandroid:id="@+id/main_et_url"android:layout_width="match_parent"android:layout_height="wrap_content" /></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal" ><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="输入保存的文件名:" /><EditTextandroid:id="@+id/main_et_name"android:layout_width="match_parent"android:layout_height="wrap_content" /></LinearLayout><Buttonandroid:id="@+id/main_btn_download"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="下载" /><ProgressBarandroid:id="@+id/main_progressBar"style="@android:style/Widget.ProgressBar.Horizontal"android:layout_width="match_parent"android:layout_height="wrap_content" /></LinearLayout>

权限：

<!-- 在SD卡中创建与删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 向SD卡写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<!-- 授权访问网络 -->
<uses-permission android:name="android.permission.INTERNET"/>

 

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