downloadthread.java

android4.0网络编程详解

package com.wangjialin.internet.service.downloader;

import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

import android.util.Log;

/**
 * 下载线程，根据具体下载地址、保持到的文件、下载块的大小、已经下载的数据大小等信息进行下载
 * @author Wang Jialin
 *
 */
public class DownloadThread extends Thread {
	private static final String TAG = "DownloadThread";	//定义TAG，方便日子的打印输出
	private File saveFile;	//下载的数据保存到的文件
	private URL downUrl;	//下载的URL
	private int block;	//每条线程下载的大小
	private int threadId = -1;	//初始化线程id设置
	private int downloadedLength;	//该线程已经下载的数据长度
	private boolean finished = false;	//该线程是否完成下载的标志
	private FileDownloader downloader;	//文件下载器
	
	public DownloadThread(FileDownloader downloader, URL downUrl, File saveFile, int block, int downloadedLength, int threadId) {
		this.downUrl = downUrl;
		this.saveFile = saveFile;
		this.block = block;
		this.downloader = downloader;
		this.threadId = threadId;
		this.downloadedLength = downloadedLength;
	}
	
	@Override
	public void run() {
		if(downloadedLength < block){//未下载完成
			try {
				HttpURLConnection http = (HttpURLConnection) downUrl.openConnection();	//开启HttpURLConnection连接
				http.setConnectTimeout(5 * 1000);	//设置连接超时时间为5秒钟
				http.setRequestMethod("GET");	//设置请求的方法为GET
				http.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, */*");	//设置客户端可以接受的返回数据类型
				http.setRequestProperty("Accept-Language", "zh-CN");	//设置客户端使用的语言问中文
				http.setRequestProperty("Referer", downUrl.toString()); 	//设置请求的来源，便于对访问来源进行统计
				http.setRequestProperty("Charset", "UTF-8");	//设置通信编码为UTF-8
				int startPos = block * (threadId - 1) + downloadedLength;//开始位置
				int endPos = block * threadId -1;//结束位置
				http.setRequestProperty("Range", "bytes=" + startPos + "-"+ endPos);//设置获取实体数据的范围,如果超过了实体数据的大小会自动返回实际的数据大小
				http.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 8.0; 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)");	//客户端用户代理
				http.setRequestProperty("Connection", "Keep-Alive");	//使用长连接
				
				InputStream inStream = http.getInputStream();	//获取远程连接的输入流
				byte[] buffer = new byte[1024];	//设置本地数据缓存的大小为1M
				int offset = 0;	//设置每次读取的数据量
				print("Thread " + this.threadId + " starts to download from position "+ startPos);	//打印该线程开始下载的位置
				RandomAccessFile threadFile = new RandomAccessFile(this.saveFile, "rwd");	//If the file does not already exist then an attempt will be made to create it and it require that every update to the file's content be written synchronously to the underlying storage device. 
				threadFile.seek(startPos);	//文件指针指向开始下载的位置
				while (!downloader.getExited() && (offset = inStream.read(buffer, 0, 1024)) != -1) {	//但用户没有要求停止下载，同时没有到达请求数据的末尾时候会一直循环读取数据
					threadFile.write(buffer, 0, offset);	//直接把数据写到文件中
					downloadedLength += offset;	//把新下载的已经写到文件中的数据加入到下载长度中
					downloader.update(this.threadId, downloadedLength);	//把该线程已经下载的数据长度更新到数据库和内存哈希表中
					downloader.append(offset);	//把新下载的数据长度加入到已经下载的数据总长度中
				}//该线程下载数据完毕或者下载被用户停止
				threadFile.close();	//Closes this random access file stream and releases any system resources associated with the stream.
				inStream.close();	//Concrete implementations of this class should free any resources during close
				if(downloader.getExited())
				{
					print("Thread " + this.threadId + " has been paused");
				}
				else
				{
					print("Thread " + this.threadId + " download finish");
				}
				
				this.finished = true;	//设置完成标志为true，无论是下载完成还是用户主动中断下载
			} catch (Exception e) {	//出现异常
				this.downloadedLength = -1;	//设置该线程已经下载的长度为-1
				print("Thread "+ this.threadId+ ":"+ e);	//打印出异常信息
			}
		}
	}
	/**
	 * 打印信息
	 * @param msg	信息
	 */
	private static void print(String msg){
		Log.i(TAG, msg);	//使用Logcat的Information方式打印信息
	}
	
	/**
	 * 下载是否完成
	 * @return
	 */
	public boolean isFinished() {
		return finished;
	}
	
	/**
	 * 已经下载的内容大小
	 * @return 如果返回值为-1,代表下载失败
	 */
	public long getDownloadedLength() {
		return downloadedLength;
	}
}