rt

下面是用socket和servlet进行通讯的客户端代码，要注意，JAVA的权限要求，在APPLET中进行socket通讯，servlet和APPLET的WEB服务器必须在一个IP地址上
    con = url.openConnection();
      //设置连接属性
      con.setDoInput(true);
      con.setDoOutput(true);
      con.setUseCaches(false);
      //取得输出流
      writer = new PrintWriter(con.getOutputStream());

      //输出对象
      writer.println(argInput);
      writer.flush();
      writer.close();
      //取得输入流
      reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
      String buffer = reader.readLine();

需要修改一个文件，路径是： “你的jdk的目录“jrelibsecurityjava.policy。
在文件中加入代码：
permission java.net.SocketPermission "-", "listen";
permission java.net.SocketPermission "-", "accept";
permission java.net.SocketPermission "-", "connect";
permission java.net.SocketPermission "-", "read";
permission java.net.SocketPermission "-", "write";

ServerSocket serverSocket = null;
    private DataOutputStream outStream = null; 
    private DataInputStream inStream = null;      
        try {
            serverSocket = new ServerSocket(port);
   
            socket = serverSocket.accept();

            //initialize socket,outStream
            inStream = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
            outStream = new DataOutputStream(new BufferedOutputStream(socket.getOutputStream()));

            //receive Msg from client
            int len = inStream.readInt();
            //if(len 0) {
                    int k=inStream.read(readBytes,i,j);
                    i=i+k;
                    j=j-k;
            }
            String clientMsg = new String(readBytes,0,len,"GB2312");

            //send Ack to client
            byte[] sendBytes = null;

                sendBytes = "error".getBytes("GB2312");
                outStream.writeInt(sendBytes.length);
                outStream.write(sendBytes);
                outStream.flush();
                outStream.close();
                socket.close();
        }
        catch(Exception e) {
            if(socket != null) {
                socket.close();
            }
            if(outStream != null) {
                outStream.close();
            }
            if(inStream != null) {
                inStream.close();
            }
        }

Socket s = new Socket(hostIP,hostPort);