Java SE 多线程下载网络上的文件代码+注释

缺乏、安全感 2022-08-05 13:29 121阅读 0赞

import java.io.InputStream;
    import java.io.RandomAccessFile;
    import java.net.HttpURLConnection;
    import java.net.URL;
    
    import org.junit.Test;
    
    
    public class DownLoader {
        
        @Test
        public void download() throws Throwable{
            String filename = "baiduTool.exe";
            String path ="http://dlsw.baidu.com/sw-search-sp/soft/e2/28619/BaiduExpert_Setup_2.0.201.1910.1422515416.exe";
            URL url = new URL(path);
            HttpURLConnection conn =(HttpURLConnection)url.openConnection();
            conn.setConnectTimeout(5*1000);
            conn.setRequestMethod("GET");
            int filelength = conn.getContentLength();//文件的长度
            System.out.println(filelength);
    
            RandomAccessFile file = new RandomAccessFile(filename, "rw");//得到随机文件类，第一个参数为文件名称，第二个参数是对文件的操作，rw是读写操作
    
            file.setLength(filelength);//设置本地文件的长度，等于本地文件的长度
            file.close();//关闭这个文件
            conn.disconnect();//先断掉这个链接，这个方法不调用也可以的
    
            int threadsize = 3;//设置要下载的线程数
            int threadlength = filelength %3 == 0?filelength/3:filelength/3+1;//每条线程下载的长度
            for(int i= 0;i<threadsize;i++){
                int startposition = i* threadlength;//计算每条线程应该从文件的什么位置开始下载
                RandomAccessFile threadfile = new RandomAccessFile(filename, "rw");
                threadfile.seek(startposition);//从文件的什么位置开始写入数据
                new DownLoadThread(i,path,startposition,threadfile,threadlength).start();
            }
            int quit =System.in.read();
            while('q' != quit){
                Thread.sleep(2*1000);
            }
        }
    
        private class DownLoadThread extends Thread{
        
            private int threadid;
            private int startpositon;
            private RandomAccessFile threadFile;
            private int threadlength;
            private String path;
            public DownLoadThread(int threadid,String path,int startposition,RandomAccessFile threadFile,int threadlength){
                this.threadid = threadid;
                this.path= path;
                this.startpositon= startposition;
                this.threadFile = threadFile;
                this.threadlength =threadlength;
    
            }
    
            @Override
            public void run(){
                try {
                    URL url = new URL(path);
                    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                    conn.setConnectTimeout(5*1000);
                    conn.setRequestMethod("GET");
                    conn.setRequestProperty("Range","bytes="+startpositon+"-");//从指定文件从什么位置开始下载
    
                    InputStream inStream = conn.getInputStream();
                    byte[] buffer = new byte[1024];
                    int len =-1;
                    int length =0;//指的是当前线程下载的值，之后将下载的长度和每个线程下载的长度进行比较，如果小于就继续下载，如果大于就停止下循环
                    while(length<threadlength &&(len = inStream.read(buffer))!=-1){
                        threadFile.write(buffer,0,len);
                        length +=len;//累计下载长度
                        //当复制到第二条线程的时候，已经制定了开始写位置，写到自己的长度就应该断掉
                    }
                    threadFile.close();
                    inStream.close();
                    System.out.println("线程"+(threadid+1)+"已经下载完成");
                } catch (Exception e) {
                    System.out.println("线程"+(threadid+1)+"下载出错了"+e);
    
                }
            }
    
        }
    
    }