多线程下载

Posted 2020-08-12

package 多线程下载;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;
import java.net.URLConnection;
/**
 * 
 * 1.获取到服务器资源文件的大小
 *     conn.getContentLength()
 * 2.根据开启的线程的数量，把服务器的资源给等等成若干份
 *     threadCount
 * 每个区块的大小：
 * int blocksize = length/threadcount
 * 3.随机访问文件流，
 * RandomAccessFile
 * 4.根据http协议
 * conn.
 * 安卓客个户端“
 * 创建
 * 
 * 
 * @author Administrator
 *
 */
public class MultileThread {
     /**
     * 线程的数量
     * @param args
     */
    private static int  threadCount = 3;
    /**
     * 每个区块的大小
     * @param args
     */
    private static long blockSize;
    /**
     * 正在运行的线程的数量
     * @param args
     */
    private static int runningThreadCount;
    private static HttpURLConnection conn;
    public static void main(String[] args) {
    try {
        String path = "http://localhost:8080/";
        //获取服务器文件路径
        URL url = new URL(path);
        conn = (HttpURLConnection) url.openConnection();
        //设置连接参数
        conn.setRequestMethod("GET");
        //获取响应码
        int code = conn.getResponseCode();
        if(code == 206){//分段下载资源的响应码
            long size = conn.getContentLengthLong();//得到服务端返回的文件大小
            System.out.println("服务器文件大小："+size);
            blockSize = size /threadCount;
        
            //首先在本地创建一个大小跟服务器一模一样的空白文件
            File file = new File("temp.exe");
            RandomAccessFile raf = new RandomAccessFile(file,"rw");//rw模式，文件不存在会自动创建
            //设置长度与服务器文件一致
            raf.setLength(size);
            //开启若干个子线程分别去下载对应的资源
            runningThreadCount = threadCount;
            for(int i = 1;i <= 3;i++){
                long startIndex = (i - 1)*blockSize;//文件下载起始位置从0开始
                long endIndex = i *blockSize-1;
                if(i==threadCount){
                    //最后一个线程
                    endIndex = size -1;
                }
                System.out.println("开启线程："+i +"    线程的位置："+startIndex+"-"+endIndex);
                //开启线程
                
            }
        }
    
    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }finally{
        conn.disconnect();//取消连接
    }
}
    private class MyThread extends Thread{
        private long startIndex;
        private long endIndex;
        private int threadId;
        private String path;
        
        public MyThread(long startIndex, long endIndex, int threadId,
                String path) {
            super();
            this.startIndex = startIndex;
            this.endIndex = endIndex;
            this.threadId = threadId;
            this.path = path;
        }

        @Override
        public void run() {
            try {
                //当前线程下载的总大小
                int total = 0;
                File positionFile = new File(threadId+".txt");
                URL url = new URL("path");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
            /*    //从上一次的位置继续下载数据
                if(positionFile.exists()&&positionFile.length()>0){//判断是否有记录    
                }*/
                
                
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (ProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}