Android的网络应用-使用HttpURLConnection
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>
