Java server program doesn't accept the input from client at second run of client

Question

I wrote a small client server program in Java. Server creates a ServerSocket on some port and keeps listening to it. Client sends some sample info to this server. When I run Client the first time connection is accepted by server and info is printed by server. Then Client program exits. When I run Client again, connection is accepted however, data is not printed. Please check following code.

Server Program

package javadaemon;

import java.io.DataInputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class MyDaemon {
    public static void main(String [] args) throws IOException {
            ServerSocket ss = new ServerSocket(9879);
            ss.setSoTimeout(0);
        while(true) {
            Socket s = ss.accept();
            System.out.println("socket is connected? "+s.isConnected());
            DataInputStream dis = new DataInputStream(s.getInputStream());
            System.out.println("Input stream has "+dis.available()+" bytes available");
            while(dis.available() > 0) {
                System.out.println(dis.readByte());
            }
        }
    }
}

Client Program

package javadaemon;

import java.io.*;
import java.net.Socket;

public class Client {
public static void main(String [] args) {
    try {
        System.out.println("Connecting to " + "127.0.0.1"
                            + " on port " + 9879);
        Socket client = new Socket("127.0.0.1", 9879);
        System.out.println("Just connected to "
                    + client.getRemoteSocketAddress());
        OutputStream outToServer = client.getOutputStream();
        DataOutputStream out = new DataOutputStream(outToServer);

        for(int i=0; i<100; i++ ) {
            out.writeUTF("Syn "+i);
        }

    } catch(IOException e) {
    }
}
}

Please help me in finding why next time no data is received by server.

Avoid using empty `catch` blocks , they defeat the purpose of Exception Handling — Extreme Coders, May 26 '13 at 14:33
By the way eating exceptions isn't doing any good specially when your program isn't working correctly and you want to debug it. — Ravi K Thapliyal, May 26 '13 at 14:33

Stony · Accepted Answer · 2013-05-26T14:58:10.450

The reason is before server side receive data, the Client already exits, I just debug it. (Can't explain whey it works at the first time.) Just change your code like the below, and it works.

package javadaemon;

import java.io.DataInputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;



public class MyDaemon {
    public static void main(String [] args) throws IOException {
            ServerSocket ss = new ServerSocket(9879);
            ss.setSoTimeout(0);
        while(true) {
            Socket s = ss.accept();
            System.out.println("socket is connected? "+s.isConnected());
            DataInputStream dis = new DataInputStream(s.getInputStream());
            System.out.println("Input stream has "+dis.available()+" bytes available");
            while(true) {
                try {
                    System.out.println(dis.readByte());
                } catch (Exception e) {
                    break;
                }
            }
        }
    }
}

The Client must add flush before exits,

package javadaemon;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;

public class Client {
public static void main(String [] args) {
    try {
        System.out.println("Connecting to " + "127.0.0.1"
                            + " on port " + 9879);
        Socket client = new Socket("127.0.0.1", 9879);
        System.out.println("Just connected to "
                    + client.getRemoteSocketAddress());
        OutputStream outToServer = client.getOutputStream();
        DataOutputStream out = new DataOutputStream(outToServer);

        for(int i=0; i<100; i++ ) {
            out.writeUTF("Syn "+i);
        }
        out.flush();
        try {
             Thread.sleep(1000L);
        } catch (InterruptedException e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
    } catch(IOException e) {
        e.printStackTrace();
    }
}
}

I am seeing from couple of other sources like these http://stackoverflow.com/questions/11982693/available-of-datainputstream-from-socket, that .available() method of DataInputStream is not reliable when used with Sockets. Maybe that's what was causing the problem — Shades88, May 26 '13 at 18:42
He is not `flushing` the stream and `closing` the *client* socket. That's his problem. — Ravi Trivedi, May 26 '13 at 22:33

score 0 · Answer 2 · answered May 26 '13 at 22:32

Place this in your Client program after for loop:

out.flush();
out.close();
client.close();

You need to flush your stream in order to push the data forward and clean the stream. Also, you will need to close your client socket.

I just tested this successfully.

Java server program doesn't accept the input from client at second run of client

2 Answers2