multithreadgetfile.java

java多线程下载实现断点续传--- --- --- --

package down;
/**
 * 多线程下载调度程序
 */
import java.io.File;

import java.net.HttpURLConnection;
import java.net.URL;
import java.util.StringTokenizer;


public class MultiThreadGetFile extends Thread
{
  long startPos=0,endPos=0;
  String currentFileThreadName;//要带上完整的路径
  String urlFile;//网络文件地址
  String urlFileName;//网络文件名
  String localFileAddress;//下载文件要存放的地址
  int threadNum;//要同时下载的线程数
  long[] eachThreadLength;//每个线程要下载的文件分块的大小
  long urlFileLength;//网络文件的大小
  URL url;
  HttpURLConnection httpURLConnection;
  public static boolean[] checkList;//检测线程
  public MultiThreadGetFile(String urlFile,int threadNum,String localFileAddress)
  {
    this.urlFile=urlFile;
    this.threadNum=threadNum;//要同时下载的线程数
    this.localFileAddress=localFileAddress;
    
  }
  private void init_getEachThreadLength()//确定每个线程文件最终要写的文件在大小
  {
    long l;
    l=urlFileLength/threadNum;
    for(int i=0;i<threadNum;i++)
    {
      if(i==threadNum-1)//如果是分配最后一个线程了
      {
        eachThreadLength[i]=urlFileLength-i*l;
      }
      else
        eachThreadLength[i]=l;
    }
  }
  private String GetFileName(String file)
  {
    StringTokenizer st=new StringTokenizer(file,"/");
    while(st.hasMoreTokens())
    {
      file=st.nextToken();
    }
    return file;
  }
  private void init()
  {
	File file1 = new File(localFileAddress+"tmp");
    if(!file1.mkdir())//创建一个临时文件夹
    {
      System.out.println("创建文件夹失败！");
    }
    eachThreadLength=new long[threadNum];
    try
    {
      url=new URL(urlFile);
      httpURLConnection=(HttpURLConnection)url.openConnection();
      urlFileLength=Long.parseLong(httpURLConnection.getHeaderField("Content-Length"));      
      urlFileName=url.getFile();//取得在服务器上的路径及文件名
      urlFileName=GetFileName(urlFileName);//只得文件名
      init_getEachThreadLength();
      httpURLConnection.disconnect();
      checkList=new boolean[threadNum+1];
      for(int i=1;i<=threadNum;i++)
      {
        if(i>1)
          startPos=startPos+eachThreadLength[i-2];
        endPos=startPos+eachThreadLength[i-1];
        currentFileThreadName=localFileAddress+"tmp\\"+urlFileName+".part"+i;
        //System.out.println("thteadNum"+(i)+":");
        //System.out.println("startPos:"+(startPos));
        //System.out.println("endPos:"+(endPos));
        //System.out.println("Size:"+(endPos-startPos));
        Thread thread=new Thread(new GetFileThread(urlFile,startPos,endPos,currentFileThreadName,i));
        thread.start();
        checkList[i]=false;//表示该线程开始
      }
      Thread policeThread=new Thread(new PoliceThread(threadNum,localFileAddress,localFileAddress+"tmp"));
      policeThread.start();
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  }
  public void run()
  {
    init();
  }
}