InputStreamReader returns null

[Rob Brew]

HI all

I'm writing the word "load" to a server and expexting a reply in the form of a string array. The program exits on readLine() returning null

ackage battleserver;
/* ChatServer.java */
import java.net.ServerSocket;
import java.net.Socket;

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;


class BattleServer {
    private static int port = 1001; /* port to listen on */
    private static String[] sArray = new String[3];
    
    public static void main (String[] args) throws IOException {

        class ClientConn implements Runnable {
            private Socket client;

            ClientConn(Socket client) {
                
                
                this.client = client;
                
            }

            public void run() {
                sArray = init();
                BufferedReader in = null;
                PrintWriter out = null;
                try {
                    /* obtain an input stream to this client ... */
                    in = new BufferedReader(new InputStreamReader(
                                client.getInputStream()));
                    /* ... and an output stream to the same client */
                    out = new PrintWriter(client.getOutputStream(), true);
                } catch (IOException e) {
                    System.err.println(e);
                    return;
                }
                try {
                
                String msg = in.readLine();
                System.out.println("msg = " + msg);
                
                    /* loop reading messages from the client, 
                     * output to stdin and send back an "OK" back */
                if (msg.equals("load")) {        
                System.out.println("sArray out " + sArray[0]);
                        out.println(sArray[0]);
                        out.flush();
                        System.out.println("sArray out " + sArray[1]);
                        out.println(sArray[1]);
                        out.flush();
               System.out.println("sArray out " + sArray[2]);
                        out.println(sArray[2]);
                        out.flush();
                }
                else {
                    sArray[0] = in.readLine();
                    sArray[1] = in.readLine();
                    sArray[2] = in.readLine();
                    System.out.println("saved " + sArray[0]);
                }
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
                
            }
        }

        ServerSocket server = null;
        try {
            server = new ServerSocket(port); /* start listening on the port */
        } catch (IOException e) {
            System.err.println("Could not listen on port: " + port);
            System.err.println(e);
            System.exit(1);
        }

        Socket client = null;
        while(true) {
            try {
                client = server.accept();
            } catch (IOException e) {
                System.err.println("Accept failed.");
                System.err.println(e);
                System.exit(1);
            }
            /* start a new thread to handle this client */
            Thread t = new Thread(new ClientConn(client));
            t.start();
        }
    }


    static public String[] init() {
        int x[] = new int[4];
        int y[] = new int[4];
        String sArray[] = new String[3];
        String s = "";
        int z = 0;

        for (int k = 0; k < 3; k++) {
            int startx = (int) (Math.random() * 7);
            int starty = (int) (Math.random() * 7);
            int length = (int) (Math.random() * 7);
            int direction = (int) (Math.random() * 2);

            switch (direction) {
                case 0:
                    for (int j = 0; j <= 3; j++) {
                        y[j] = starty;
                        x[j] = startx + j;
                    }
                    break;
                case 1:
                    for (int j = 0; j <= 3; j++) {
                        x[j] = startx;
                        y[j] = starty + j;
                    }
                    break;
                default:
                    System.out.println("error");
            }
            for (int i = 0; i < x.length; i++) {
                s = s + Integer.toString(x[i]);
            }
            s = s + " ";
            for (int i = 0; i < y.length; i++) {
                s = s + Integer.toString(y[i]);
            }
            sArray[z] = s;
            z++;

            x = new int[4];
            y = new int[4];
            s = "";
        }

        return sArray;

    }
}
]

package battleships;

/* ChatClient.java */
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintWriter;

import java.net.Socket;
import java.net.UnknownHostException;

public class ChatClient {
    private static int port = 1001; /* port to connect to */
    private static String host = "localhost"; /* host to connect to */
   String[] sArray = new String[3];

    
    public ChatClient (String[] toSend) throws IOException {

        Socket server = null;
        sArray = toSend;
        try {
            /* try to open a socket to the server at the given host:port */
            server = new Socket(host, port);
        } catch (UnknownHostException e) {
            System.err.println(e);
            System.exit(1);
        }
        
        /* obtain an output stream to the server... */
        PrintWriter out = new PrintWriter(server.getOutputStream(), true);
        /* ... and an input stream */
        InputStreamReader isr = new InputStreamReader(server.getInputStream());
        System.out.println("isr = " + isr.ready());
        BufferedReader in = new BufferedReader(isr);
        
         
               
        /* loop reading messages from stdin, send them to the server 
         * and read the server's response */
        if ( (toSend == null))
        {
            out.println("load");
            
        System.out.println("in = " + in.ready());
        sArray[0] = in.readLine();
        sArray[1] = in.readLine();
        sArray[2] = in.readLine();
        System.out.println(sArray[0] + " first string");
        }
        else {
            out.println("save");
            out.println(sArray[0]);
            out.println(sArray[1]);
            out.println(sArray[2]);
            out.flush();
            System.out.println("written array to server");
        }
    }
        public String[] getS () {
            return sArray;
        }
    }

[Paul Clapham]

You call the method several times, and you didn't say which of them causes the problem, so let me simply point out that BufferedReader's readLine() method is designed to return null after it reaches the end of its underlying data stream. There's nothing abnormal about that. It's up to your code to deal with the possibility.

[Rob Brew]

the null pointer exception occurs at line 46 of the ClientChat Class. The program battleserver claims to be sending data to the pipe.