Java实现文件断点续传

package com.chinacick.yummy.Httpftp.test;

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

  

public classDownloadFile {

  

    /**

     * @param args

     */

    staticint len;//线程平均下载文件长度

    staticint bn ;//每个线程写入文件的字节数

    staticint tn; //线程数

    staticString urlt;//下载地址

    staticString fileName;

    staticRandomAccessFile osf; //文件操作

    publicstatic void main(String[] args) {

        // TODO Auto-generated method stub

          

        try{

            urlt ="http://192.168.16.77:8080/Stargreat/html/baidu player";

            fileName ="C:\" + urlt.split("//")[1].split("/")[urlt.split("//")[1].split("/").length-1];

            System.out.println(fileName);

            URL url =new URL(urlt);

            HttpURLConnection http = (HttpURLConnection) url.openConnection();

  

            /**

             * 此处设定5个线程下载一个文件tn = 5;

             * 判断平均每个线程需下载文件长度：

             */

            System.out.println("file size:"+ http.getContentLength());

            tn =3;        

            len = http.getContentLength() / tn ;//舍去余数（余数自动舍去）计算每个线程应下载平均长度，最后一个线程再加上余数，则是整个文件的长度,

            File f =new File(fileName);

            if(f.exists()){

                f.delete();

                osf =new RandomAccessFile(f, "rw");

                osf.seek(http.getContentLength()-1);

                osf.write(0);

            }else{

                osf =new RandomAccessFile(f, "rw");

                osf.seek(http.getContentLength()-1);

                osf.write(0);

            }

            System.out.println("temp 文件长度："+ f.length());

            Thread t;//下载子线程，

            for(int j = 0; j < tn; j++) {

                if(j == tn -1){//如果最后一个线程则加上余数长度字节

                    bn = len + (http.getContentLength() % tn);

                }else{

                    bn = len;

                }

                System.out.println("t"+ j +"线程下载长度：" + bn + "起始字节："+ len*j);

                t =new DT(

                        j,

                        urlt,

                        fileName,

                        len*j,

                        bn

                          

                );

                t.start();

            }

  

        } catch (IOException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

  

}

 

 

//该代码片段来自于: http://www.sharejs.com/codes/java/6863

package com.chinacick.yummy.Httpftp.test;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.MalformedURLException;

import java.net.URL;

import java.util.Date;

  

  

public classDT extends Thread {

  

    String urlt;//下载地址

    intstartl;//子线程读取/写入起始字节

    intend;//子线程写入结束字节长度

    String fileName;

    RandomAccessFile osf;

    publicDT(int i ,String url,String fileName,int start,int end){

        this.setName("t"+i);//子线程名称

        this.urlt = url;//下载地址

        this.fileName = fileName;

        this.startl = start;//子线程读取/写入起始字节

        this.end = end;//子线程写入结束字节长度

    }

    publicvoid run(){

            try{

                osf =new RandomAccessFile(fileName,"rw");

                URL url =new URL(urlt);

                HttpURLConnection http2 = (HttpURLConnection) url.openConnection();

                http2.setRequestProperty("User-Agent","NetFox");

              

                /*

                 * 断点续传和多线程下载的关键代码关键位置：即设置断点

                 * http2.setRequestProperty("RANGE", "bytes="+startl+"-");//设置断点位置，向服务器请求从文件的哪个字节开始读取。

                 * osf.seek(startl);//设置本地文件从哪个字节开始写入

                 * 如果是单线程，则首先要判断下载文件是否已经存在 及DownloadFile.java 里的 fileName = "C:\eclipse.zip";

                 * 如果存在则开始断点续传，方法同多线程：

                 * 因为断点续传是从上次传输中断的字节开始，则首先要得到上次中断的位置，既是文件长度（针对单线程）f.length()

                 * 然后设置HTTP请求头属性RANGE，该属性告知服务器从哪个自己开始读取文件。

                 * 设置本地文件写入起始字节，及接从上次传输断点继续写入（断点续传）

                 * osf.seek(offset) 该方法设定从offset后一个字节开始写入文件

                 * 注意：多线程不能用文件长度做为写文件起始字节，需有配置文件记录上次读写的位置，迅雷下载既是使用该种方法。

                 *

                 */

                http2.setRequestProperty("RANGE","bytes="+startl+"-");//设置断点位置，向服务器请求从文件的哪个字节开始读取。

                osf.seek(startl);//设置本地文件从哪个字节开始写入

                  

                InputStream input = http2.getInputStream();

                byteb[] = new byte[1024];//设置缓冲池，每次只读1024字节

                Date d =new Date();//子线程开始下载时间

                intl;//计算子线程读取和写入的文件长度，当长度大于每个子线程平均下载长度则终止线程

                inti;

                l =0;

                System.out.println(this.getName() +" 开始下载。。。");

                while( (i = input.read(b,0,1024)) != -1&& l < end){    //线程下载字节长度控制误差小于缓冲池大小，本示例为缓冲池1024字节

                    osf.write(b,0, i);

                    b =new byte[1024];//重新赋值，避免重新读入旧内容

                    l += i;        

                }

                Date d2 =new Date();//子线程结束下载时间

                System.out.println(this.getName() +" 线程耗时： " + (d2.getTime() - d.getTime())/1000+ " 秒,实际共下载：" + l + "字节");//子线程下载耗时（秒）

            }catch (FileNotFoundException e1) {

                // TODO Auto-generated catch block

                e1.printStackTrace();

            }catch (MalformedURLException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }catch (IOException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

    }

}

//该代码片段来自于: http://www.sharejs.com/codes/java/6863