tcp client server communication

i am not been able to find the error in the program server:

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

public class Server { public static void main(String[] args) throws Exception { String clientSentence; String sentence;

    ServerSocket welcomeSocket = new ServerSocket(6787);
    Socket connectionSocket = welcomeSocket.accept();
    BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
    DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
    BufferedReader serverInput = new BufferedReader(new InputStreamReader(System.in));

    sentence = serverInput.readLine();
    outToClient.writeBytes(sentence + '\n');

    while((clientSentence = inFromClient.readLine()) != null) {

        if(clientSentence.equals("exit"))
            break;

        System.out.println("FROM CLIENT:  " + clientSentence);

        if (serverInput != null) {
            sentence = serverInput.readLine();
            outToClient.writeBytes(sentence + '\n');
            if (sentence.equals("exit"))
                break;
        }
    }

    welcomeSocket.close();
    connectionSocket.close();
    inFromClient.close();
    outToClient.close();
    serverInput.close();
}

}

client:

import java.io.*;

import java.net.*;

public class Client { public static void main(String[] args) throws Exception { String sentence; String modifiedSentence; BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket = new Socket("hostname", 6787); DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream()); BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

    while((modifiedSentence = inFromServer.readLine()) != null){
        if (modifiedSentence.equals("exit"))
            break;

        System.out.println("FROM SERVER:  " + modifiedSentence);

        sentence = inFromUser.readLine();

        if (inFromUser != null) {
            outToServer.writeBytes("Typed:"+sentence + '\n');
            if(sentence.equals("exit"))
                    break;
        }


    }

    clientSocket.close();
    inFromUser.close();
    outToServer.close();
    inFromServer.close();

}

}