Java Socket connection from app to java server

Question

I am setting up an chat app. I have a server, written in java with socket, that connects perfectly to an example code in java. But when I try the exact same code with android studio over the app it doesnt work for some reason.

I have tried to run it with a code outside of the app and it worked. I have got the user permissions on so it can connect to the internet. I have tried to connect to the server on the console and it worked.

The client:

class Client implements Runnable{
    int freePort;

    @Override
    public void run() {
        connect();
    }

    private void connect(){
        System.out.println("Connecting");
        try {
            Socket socket = new Socket("localhost",1336);
            System.out.println("Connected");
            DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
            freePort = dataInputStream.readInt();
            System.out.println(freePort);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}

The server:


import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;

public class DeclarationServer {
    private int numberOfClients = 0;
    DeclarationServer(){
        try {
            ServerSocket serverSocket = new ServerSocket(1336);
            while (true) {
                System.out.println(serverSocket.getLocalPort() + "__" + serverSocket.getLocalSocketAddress());
                Socket socket = serverSocket.accept();

                System.out.println(socket.getLocalSocketAddress());
                DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
                dataInputStream.readUTF();
                DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
                dataOutputStream.writeInt(1339+numberOfClients);
                dataOutputStream.flush();
                dataOutputStream.close();
                numberOfClients++;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


    }
}

The error message:

I/System.out: Connecting
D/ActivityThread: add activity client record, r= ActivityRecord{5f45e99 token=android.os.BinderProxy@712539a {com.example.birke.testapp/com.example.birke.testapp.MainActivity}} token= android.os.BinderProxy@712539a
D/ZrHung.AppEyeUiProbe: notify runnable to start.
W/System.err: java.net.ConnectException: failed to connect to localhost/127.0.0.1 (port 1336) from /:: (port 32940): connect failed: ECONNREFUSED (Connection refused)
        at libcore.io.IoBridge.connect(IoBridge.java:137)
        at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:137)
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:391)
        at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:231)
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:213)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:436)
        at java.net.Socket.connect(Socket.java:621)
        at java.net.Socket.connect(Socket.java:570)
        at java.net.Socket.<init>(Socket.java:450)
        at java.net.Socket.<init>(Socket.java:218)
W/System.err:     at com.example.birke.testapp.Client.connect(MainActivity.java:151)
        at com.example.birke.testapp.Client.run(MainActivity.java:145)
        at java.lang.Thread.run(Thread.java:784)
    Caused by: android.system.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
        at libcore.io.Linux.connect(Native Method)
        at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:118)
        at libcore.io.IoBridge.connectErrno(IoBridge.java:151)
        at libcore.io.IoBridge.connect(IoBridge.java:129)
        ... 12 more

10.0.2.2 should be the port you should be connecting to from the app. — Dinesh, Oct 12 '19 at 19:40

score 0 · Accepted Answer · answered Oct 12 '19 at 19:49

Look into this line,

failed to connect to localhost/127.0.0.1 (port 1336) from /:: (port 32940): connect failed: ECONNREFUSED (Connection refused)

That means, the localhost is refusing the connection most probably, the service/server is not running on the specific port. You would be able to connect to the localhost if the server was running in the same android device.

Solution

Pass the IP (private IP if both client and server are in the same network otherwise public IP) of the server instead of localhost while initializing Socket,

Socket socket = new Socket("192.168.XXX.XXX",1336);

Java Socket connection from app to java server

1 Answers1