Java多线程下载文件实例详解

本文实例为大家分享了java多线程下载文件的具体代码，供大家参考，具体内容如下

import java.io.file; 
import java.io.inputstream; 
import java.io.randomaccessfile; 
import java.net.httpurlconnection; 
import java.net.url; 
 
public class multhreaddownload { 
  public static void main(string[] args) throws exception { 
    string path = "http://192.168.1.100:8080/hello/big.exe"; 
    new multhreaddownload().download(path, 3); 
  } 
 
  /** 
   * 下载文件 
   * 
   * @param path 
   *      网络文件路径 
   * @param threadsize 
   *      线程数 
   * @throws exception 
   */ 
  private void download(string path, int threadsize) throws exception { 
    url url = new url(path); 
    httpurlconnection connection = (httpurlconnection) url.openconnection(); 
    connection.setrequestmethod("get"); 
    connection.setconnecttimeout(5000); 
    if (connection.getresponsecode() == 200) { 
      int length = connection.getcontentlength();// 获取网络文件长度 
      file file = new file(getfilename(path)); 
      // 在本地生成一个长度与网络文件相同的文件 
      randomaccessfile accessfile = new randomaccessfile(file, "rwd"); 
      accessfile.setlength(length); 
      accessfile.close(); 
 
      // 计算每条线程负责下载的数据量 
      int block = length % threadsize == 0 ? length / threadsize : length 
          / threadsize + 1; 
      for (int threadid = 0; threadid < threadsize; threadid++) { 
        new downloadthread(threadid, block, url, file).start(); 
      } 
    } else { 
      system.out.println("download fail"); 
    } 
  } 
 
  private class downloadthread extends thread { 
 
    private int threadid; 
    private int block; 
    private url url; 
    private file file; 
 
    public downloadthread(int threadid, int block, url url, file file) { 
      this.threadid = threadid; 
      this.block = block; 
      this.url = url; 
      this.file = file; 
    } 
 
    @override 
    public void run() { 
      int start = threadid * block; // 计算该线程从网络文件什么位置开始下载 
      int end = (threadid + 1) * block - 1; // 计算下载到网络文件什么位置结束 
      try { 
        randomaccessfile accessfile = new randomaccessfile(file, "rwd"); 
        accessfile.seek(start); //从start开始 
 
        httpurlconnection connection = (httpurlconnection) url 
            .openconnection(); 
        connection.setrequestmethod("get"); 
        connection.setconnecttimeout(5000); 
        //设置获取资源数据的范围，从start到end 
        connection.setrequestproperty("range", "bytes=" + start + "-" 
            + end); 
        //注意多线程下载状态码是 206 不是200 
        if (connection.getresponsecode() == 206) { 
          inputstream inputstream = connection.getinputstream(); 
          byte[] buffer = new byte[1024]; 
          int len = 0; 
          while ((len = inputstream.read(buffer)) != -1) { 
            accessfile.write(buffer, 0, len); 
          } 
          accessfile.close(); 
          inputstream.close(); 
        } 
        system.out.println("第" + (threadid + 1) + "条线程已经下载完成"); 
      } catch (exception e) { 
        e.printstacktrace(); 
      } 
    } 
  } 
 
  /** 
   * 获取文件名称 
   * 
   * @param path 
   *      网络文件路径 
   * @return 
   */ 
  private string getfilename(string path) { 
    return path.substring(path.lastindexof("/") + 1); 
  } 
} 

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