Thread downloader=new Thread(){
            public void run(){
                File file = new File(filesavePath); 
                if(!file.exists()){ 
                System.out.println("文件不存在，创建"); 
                file.createNewFile();} 

                Socket server = new Socket(serverIP, 8880); 
                RandomAccessFile raf = new RandomAccessFile(file, "rw"); 
//                 通过Socket连接文件服务器 

                PrintWriter outtosocket = new PrintWriter(server 
                .getOutputStream()); 
                ; 

                outtosocket.println(downfilemessage); 
                outtosocket.flush(); 


                InputStream netIn = server.getInputStream(); 
                InputStream in = new DataInputStream( 
                new BufferedInputStream(netIn)); 
//                创建缓冲区缓冲网络数据 


                byte[] buf = new byte[20480]; 

                                
                int num = in.read(buf); 
                while (num != (-1)&&isStop!=true) //isStop（类的一个全局变量）初始化为false 
                                                        { 
                raf.write(buf, 0, num); 
                raf.skipBytes(num); 


                num = in.read(buf);//继续从网络中读取文件 
                } 


                      


                in.close(); 
                raf.close(); 
                server.close(); 


            }
        };
        downloader.start();