多线程下载和断点续传

package com.zzw.constant;

public class Contant 
{
    public static int threadCount = 3;
}

主要代码:

package com.zzw.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.zzw.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");
                    }
                }
            }
        }
        
    }
}