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
– Extreme Coders, Commented May 26, 2013 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
– Ravi K Thapliyal, Commented May 26, 2013 at 14:33

Stony · Accepted Answer · 2013-05-26 14:58:10Z

1

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();
    }
}
}

edited May 26, 2013 at 14:58

answered May 26, 2013 at 14:48

Stony

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2 Comments

Shades88 Over a year ago

I am seeing from couple of other sources like these stackoverflow.com/questions/11982693/…, that .available() method of DataInputStream is not reliable when used with Sockets. Maybe that's what was causing the problem

Ravi Trivedi Over a year ago

He is not flushing the stream and closing the client socket. That's his problem.

Ravi Trivedi · Accepted Answer · 2013-05-26 22:32:01Z

0

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.

answered May 26, 2013 at 22:32

Ravi Trivedi

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