将客户端写入服务器Java

Question

I need help. I'm making a sample queue system. When I try to write data and store it to server, the server returns an exception. I'm also a newbie on sockets so I will appreciate any help from anyone who will reply on my question.

Here's my code for Student:

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.*;

public class Student {
   public static void main(String args[]) {
      Scanner sc = new Scanner (System.in);
  try {
     Socket skt = new Socket("localhost", 1234);
     PrintWriter out = new PrintWriter(skt.getOutputStream(), true);

     System.out.println("Hello!");

     System.out.print("Please enter name: ");
     String name = sc.next();
     System.out.print("Please enter ID Number: ");
     String id = sc.next();
     String student = name +" - "+ id;
     out.print(student);

      } catch(Exception e) {
          System.out.println("Whoops! It didn't work.");
      }
   }
}

and for the server:

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.*;

public class Server {
   public static void main(String args[]) {
      Scanner sc = new Scanner (System.in);
      ArrayList<String> collector = new ArrayList<String>();

  try {
     ServerSocket srvr = new ServerSocket(1234);
     Socket skt = srvr.accept();
     BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));

     System.out.print(in.readLine());
     String x = in.readLine();
     collector.add(x);


      }
      catch(Exception e) {
         System.out.print("Whoops! It didn't work!\n");
      }
   }
}

Answer 1

You need to properly close the PrintWriter by adding an "out.close()" statement before it finishes it's execution. Since you'r enot doing that, the client socket is abruptly closed and you get an exception on the server side.

Ideally this close() should be performed inside a finally block so you make sure it's executed. Also, as pointed out in another answer, you should only read once, store it in a variable, and then do whatever you need with the value.

Example:

public class Server {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        ArrayList<String> collector = new ArrayList<String>();

        try {
            ServerSocket srvr = new ServerSocket(1234);
            Socket skt = srvr.accept();
            BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));

            final String studentInfo = in.readLine();
            System.out.print(studentInfo);
            collector.add(studentInfo);

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Whoops! It didn't work!");
        }
    }
}

student:

public class Student {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System.in);
        PrintWriter out = null;
        try {
            Socket skt = new Socket("localhost", 1234);
            out = new PrintWriter(skt.getOutputStream(), true);

            System.out.println("Hello!");

            System.out.print("Please enter name: ");
            String name = sc.next();
            System.out.print("Please enter ID Number: ");
            String id = sc.next();
            String student = name + " - " + id;
            out.print(student);
        } catch (Exception e) {
            System.out.println("Whoops! It didn't work.");
        } finally {
            if (out != null) {
                try {
                    out.close();
                } catch (Exception e) {

                }
            }
        }
    }
}

Answer 2

You need to print out more than "Whoops" in the catch block. What exception do you get? This will help you to understand what is going wrong.

Answer 3

You're reading two times, but send only once. Regarding the cause of exception, I think it occurs because the client terminates without closing connection. Add socket close statement into client's code and exception will disappear. You're going to add null into collector though