java多线程下载文件和断点下载

多线程，断点下载文件

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.URL;

import javax.print.attribute.standard.Finishings;

public class MultiDownload {

	static int ThreadCount = 3;       //代表3个进程
	static int finishedThread = 0;   //记录文件下完的数字
	//确定下载地址
	static String path = "http://192.168.13.13:8080/QQPlayer.exe";
	public static void main(String[] args) {
		
		//发送get请求，请求这个地址的资源
		try {
			URL url = new URL(path);
			HttpURLConnection conn = (HttpURLConnection) url.openConnection();
			conn.setRequestMethod("GET");
			conn.setConnectTimeout(5000);
			conn.setReadTimeout(5000);
			
			if(conn.getResponseCode() == 200){
				//拿到所请求资源文件的长度
				int length = conn.getContentLength();
				
				File file = new File("QQPlayer.exe");
				//生成临时文件
				RandomAccessFile raf = new RandomAccessFile(file, "rwd");
				//设置临时文件的大小
				raf.setLength(length);
				raf.close();
				//计算出每个线程应该下载多少字节
				int size = length / ThreadCount;
				
				for (int i = 0; i < ThreadCount; i++) {
					//计算线程下载的开始位置和结束位置
					int startIndex = i * size;
					int endIndex = (i + 1) * size - 1;
					//如果是最后一个线程，那么结束位置写死
					if(i == ThreadCount - 1){
						endIndex = length - 1;
					}
//					System.out.println("线程" + i + "的下载区间是：" + startIndex + "---" + endIndex);
					new DownLoadThread(startIndex, endIndex, i).start();
				}
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	
	
}
class DownLoadThread extends Thread{
	int startIndex;
	int endIndex;
	int threadId;
	
	public DownLoadThread(int startIndex, int endIndex, int threadId) {
		super();
		this.startIndex = startIndex;
		this.endIndex = endIndex;
		this.threadId = threadId;
	}

	@Override
	public void run() {
		//再次发送http请求，下载原文件
		try {
			File progressFile = new File(threadId + ".txt");
			//判断进度临时文件是否存在
			if(progressFile.exists()){
				FileInputStream fis = new FileInputStream(progressFile);
				BufferedReader br = new BufferedReader(new InputStreamReader(fis));
				//从进度临时文件中读取出上一次下载的总进度，然后与原本的开始位置相加，得到新的开始位置
				startIndex += Integer.parseInt(br.readLine());
				fis.close();
			}
			System.out.println("线程" + threadId + "的下载区间是：" + startIndex + "---" + endIndex);
			HttpURLConnection conn;
			URL url = new URL(MultiDownload.path);
			conn = (HttpURLConnection) url.openConnection();
			conn.setRequestMethod("GET");
			conn.setConnectTimeout(5000);
			conn.setReadTimeout(5000);
			//设置本次http请求所请求的数据的区间
			conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
			
			//请求部分数据，相应码是206
			if(conn.getResponseCode() == 206){
				//流里此时只有1/3原文件的数据
				InputStream is = conn.getInputStream();
				byte[] b = new byte[1024];
				int len = 0;
				int total = 0;
				//拿到临时文件的输出流
				File file = new File("QQPlayer.exe");
				RandomAccessFile raf = new RandomAccessFile(file, "rwd");
				//把文件的写入位置移动至startIndex
				raf.seek(startIndex);
				while((len = is.read(b)) != -1){
					//每次读取流里数据之后，同步把数据写入临时文件
					raf.write(b, 0, len);
					total += len;
//					System.out.println("线程" + threadId + "下载了" + total);
					
					//生成一个专门用来记录下载进度的临时文件
					RandomAccessFile progressRaf = new RandomAccessFile(progressFile, "rwd");
					//每次读取流里数据之后，同步把当前线程下载的总进度写入进度临时文件中
					progressRaf.write((total + "").getBytes());
					progressRaf.close();
				}
				System.out.println("线程" + threadId + "下载完毕-------------------小志参上！");
				raf.close();
				
				//把记录进程的文件删除    必须3个进程全部都下载完成后才可以删除
				MultiDownload.finishedThread++;
				synchronized (MultiDownload.path) {  //有线程安全问题，静态变量为唯一的
					if(MultiDownload.finishedThread == MultiDownload.ThreadCount){
						for (int i = 0; i < MultiDownload.ThreadCount; i++) {
							File f = new File(i + ".txt");
							f.delete();
						}
						MultiDownload.finishedThread = 0;
					}
				}
				
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}