多线程下载

package com.hx.zy.download;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

import javax.tools.FileObject;

import com.hx.zy.constant.Contant;

public class TestDownload
{
//public static int threadCount = 3;
public static int blockSize = 0;

public static void main(String[] args) throws Exception
{
URL url = new URL("http://localhost:8080/download/cc.zip");

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setReadTimeout(10000);

long length = conn.getContentLength();

conn.connect(); //连接
File file = new File("cc.zip");

RandomAccessFile randomFile = new RandomAccessFile(file,"rwd");
randomFile.setLength(length);

//每一个线程他需要下载的大小
System.out.println("总大小:" + length);
blockSize = (int) (length / Contant.threadCount);
System.out.println("每一个线程下载的大小：" + blockSize);
long start = 1;
long end = 0;
for(int i=1; i < (Contant.threadCount+1); i++)
{

//1 》》 0 - 46354938 123456
// 2 >> 46354939 -(46354939 + 46354938)
//3 》》
start = blockSize * (i -1);
end = blockSize*i -1;
if(i == Contant.threadCount)
{
end = length;
}
System.out.println("第" + i + "个线程下载的区间:" + start + " - " + end);
new downloadThread(file, i, start, end).start();
}

conn.disconnect();
}
}

class downloadThread extends Thread
{
private File path; //本地磁盘的地址
private String url = "http://localhost:8080/download/cc.zip" ; //HTTP请求的地址
private Integer threadID; //当前是第几个线程
private long start; //该线程下载的起始位置
private long end; //该线程的结束位置

public downloadThread(File path, Integer threadID, long start,
long end) {
this.path = path;
this.threadID = threadID;
this.start = start;
this.end = end;

}

@Override
public void run()
{
try {
System.out.println(threadID + "开启读取");
File contextFile = new File(threadID +".txt");
if(!contextFile.exists())
{
contextFile.createNewFile();
}

//读取断线信息里面的数据来重新的指定从哪里开始写
BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(contextFile)));
String info = reader.readLine();
if(null != info && info.length() > 0)
{
start = start + Integer.parseInt(info);
}

System.out.println("start........=" + start);
URL uri = new URL(url);
HttpURLConnection conn = (HttpURLConnection) uri.openConnection();
conn.setRequestProperty("Range", "bytes="+start +"-" + end);
conn.setReadTimeout(50000);
conn.setConnectTimeout(50000);

conn.connect();

//让http请求只请求一个片段
System.out.println("bytes="+start +"-" + end);

//判断一下是否为200？
int status = conn.getResponseCode();

if(status / 100 == 2)
{
int total = 0; //总共下载的字节数
//FileOutputStream out = new FileOutputStream(new File(threadID +".txt")); 不靠谱了
RandomAccessFile random = new RandomAccessFile(path, "rw");

random.seek(start);
InputStream in = conn.getInputStream();
byte[] buffer = new byte[1024];
int len = 0;

while((len = in.read(buffer)) != -1)
{
RandomAccessFile duandian = new RandomAccessFile(contextFile, "rwd");
random.write(buffer, 0, len);
total += len;
duandian.write(String.valueOf(total).getBytes());
duandian.close();
}
in.close();
random.close();
}
conn.disconnect();
System.out.println(threadID + "读取完成");
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally
{
synchronized (TestDownload.class)
{
Contant.threadCount --;
System.out.println("Contant.threadCount = " + Contant.threadCount);
if(Contant.threadCount == 0)
{
for(int i=1; i < 4; i++)
{
File contextFile = new File(i +".txt");
System.out.println(contextFile.delete() +" ccc");
}
}
}
}

}
}