使用HttpURLConnection实现多线程下载
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; @Override protected 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() { @Override public 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" > <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="输入url:" /> <EditText android:id="@+id/main_et_url" android:layout_width="match_parent" android:layout_height="wrap_content" /> </LinearLayout> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="输入保存的文件名:" /> <EditText android:id="@+id/main_et_name" android:layout_width="match_parent" android:layout_height="wrap_content" /> </LinearLayout> <Button android:id="@+id/main_btn_download" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="下载" /> <ProgressBar android: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"/>