Android的网络应用-使用HttpURLConnection
实例：多线程下载
实现多线程的步骤：
1.创建URL对象。
2.获取指定URL对象所指向资源的大小。
3.在本地磁盘上创建一个与网络资源相同大小的空文件。
4.计算每条线程应该下载网络资源的哪个部分（从哪个字节开始，到哪个字节结束）
5.依次创建，启动多线程来下载网络资源的指定部分
创建项目:MultiThreadDown
程序清单
下载工具类：DownUtil.java
Activity：MultiThreadDown.java
项目运行效果：
package org.wwj.net;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; // 定义下载的线程对象 private DownloadThread[] threads; // 定义下载的文件的总大小 private int fileSize; 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, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, 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; MSIE 7.0; 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(); } } // 获取下载的完成百分比 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; // 定义已经该线程已下载的字节数 public int length; public DownloadThread(int startPos, int currentPartSize, RandomAccessFile currentPart) { this.startPos = startPos; this.currentPartSize = currentPartSize; this.currentPart = currentPart; } @Override 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, image/pjpeg, application/x-shockwave-flash, application/xaml+xml, application/vnd.ms-xpsdocument, application/x-ms-xbap, 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 inStream = conn.getInputStream(); // 跳过startPos个字节，表明该线程只下载自己负责哪部分文件。 inStream.skip(this.startPos); byte[] buffer = new byte[1024]; int hasRead = 0; // 读取网络数据，并写入本地文件 while (length < currentPartSize && (hasRead = inStream.read(buffer)) != -1) { currentPart.write(buffer, 0, hasRead); // 累计该线程下载的总大小 length += hasRead; } currentPart.close(); inStream.close(); } catch (Exception e) { e.printStackTrace(); } } }}
package org.wwj.net;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;public class MultiThreadDown extends Activity{ EditText url; EditText target; Button downBn; ProgressBar bar; DownUtil downUtil; private int mDownStatus; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // 获取程序界面中的三个界面控件 url = (EditText) findViewById(R.id.url); target = (EditText) findViewById(R.id.target); downBn = (Button) findViewById(R.id.down); bar = (ProgressBar) findViewById(R.id.bar); // 创建一个Handler对象 final Handler handler = new Handler() { @Override public void handleMessage(Message msg) { if (msg.what == 0x123) { bar.setProgress(mDownStatus); } } }; downBn.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { // 初始化DownUtil对象 downUtil = new DownUtil(url.getText().toString(), target.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() { @Override 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); // 下载完全后取消任务调度 if (mDownStatus >= 100) { timer.cancel(); } } }, 0, 100); } }); }}
<!-- 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"/>
<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" ><TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="要下载的资源的URL：" /><EditText android:id="@+id/url" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="http://www.crazyit.org/attachment.php?aid=1093&k=4ec76aeaa41ee84acf667b420e926783&t=1297311085" /><TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="目标文件：" /><EditText android:id="@+id/target" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="/mnt/sdcard/a.rar" /> <Button android:id="@+id/down" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/down" /><!-- 定义一个水平进度条,用于显示下载进度 --><ProgressBar android:id="@+id/bar" android:layout_width="fill_parent" android:layout_height="wrap_content" android:max="100" style="@android:style/Widget.ProgressBar.Horizontal" /></LinearLayout>