HTTP文件下载Java编程

import java.io.RandomAccessFile;
import java.io.File;
import java.io.InputStream;
import java.io.DataInputStream;
import java.io.BufferedInputStream;
import java.io.FileInputStream;

import java.net.HttpURLConnection;
import java.net.ConnectException;
import java.net.URL;

import java.lang.Runnable;
import java.lang.Thread;

import java.util.Date;

public class TestUpDown2 implements Runnable {

private HttpURLConnection connection;//存储连接  

private int downsize = -1;//下载文件大小,初始值为-1  

private int downed = 0;//文加已下载大小,初始值为0  

private RandomAccessFile savefile;//记录下载信息存储文件  

private URL fileurl;//记录要下载文件的地址  

private DataInputStream fileStream;//记录下载的数据流  

public TestUpDown2() {
  try {
   /*开始创建下载的存储文件,并初始化值*/
   File tempfileobject = new File("C:\\200504091iis51.rar");
   if (!tempfileobject.exists()) {
    /*文件不存在则建立*/
    tempfileobject.createNewFile();
   }
   savefile = new RandomAccessFile(tempfileobject, "rw");

   /*建立连接*/
   fileurl = new URL(
     "http://localhost:9080/web_services_serverClient/sample/FileServiceProxy/200504091iis51.rar");
   connection = (HttpURLConnection) fileurl.openConnection();
   connection.setRequestProperty("Range", "byte=" + this.downed + "-");

   this.downsize = connection.getContentLength();
   //System.out.println(connection.getContentLength());  

   new Thread(this).start();
  } catch (Exception e) {
   System.out.println(e.toString());
   System.out.println("构建器错误");
   System.exit(0);
  }
}

public void run() {
  /*开始下载文件,以下测试非断点续传,下载的文件存在问题*/
  try {
   System.out.println("begin!");
   Date begintime = new Date();
   begintime.setTime(new Date().getTime());
   byte[] filebyte;
   int onecelen;
   //System.out.println(this.connection.getInputStream().getClass().getName());  
   this.fileStream = new DataInputStream(new BufferedInputStream(
     this.connection.getInputStream()));
   System.out.println("size   =   " + this.downsize);
   while (this.downsize != this.downed) {
    if (this.downsize - this.downed > 262144) {//设置为最大256KB的缓存  
     filebyte = new byte[262144];
     onecelen = 262144;
    } else {
     filebyte = new byte[this.downsize - this.downed];
     onecelen = this.downsize - this.downed;
    }
    onecelen = this.fileStream.read(filebyte, 0, onecelen);
    this.savefile.write(filebyte, 0, onecelen);
    this.downed += onecelen;
    System.out.println(this.downed);
   }
   this.savefile.close();
   System.out.println("end!");
   System.out.println(begintime.getTime());
   System.out.println(new Date().getTime());
   System.out.println(begintime.getTime() - new Date().getTime());
  } catch (Exception e) {
   System.out.println(e.toString());
   System.out.println("run()方法有问题!");
  }
}

public static void main(String[] src) throws Exception {
  new TestUpDown2();
}
}