Having problems with CharBuffer

I am trying to create a command line chat client, but my server keeps returning NullPointerException error when it gets to the CharBuffer. They connect to each other fine. It's the sending that has trouble.
Here's the code:

Code:

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package chat;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CodingErrorAction;
import java.util.Scanner;
import java.net.ServerSocket;

public class App {

        public App() throws java.io.IOException {
                this.startChat();
        }
        public static void print(String msg){
                System.out.println(msg);
        }

        public static void startChat() throws java.io.IOException {
                Scanner input = new Scanner(System.in);
                CharsetEncoder encoder = Charset.forName("US-ASCII").newEncoder();
                print("Select server/client");
                String text = input.nextLine();
                if(text.equals("server")){
                        //==================================================================
                        // SERVER
                        //==================================================================
                        print("Input port.");
                        int port = input.nextInt();
                        ServerSocketChannel server = ServerSocketChannel.open();
                        server.socket().bind(new java.net.InetSocketAddress(port));
                        for(;;){
                                print("waiting for connection...");
                                SocketChannel client = server.accept();
                                print("Connected");
                                client.write(encoder.encode(CharBuffer.wrap("test txt")));
                        }
                }
                else if(text.equals("client")){
                        //==================================================================
                        //CLIENT
                        //==================================================================
                        Socket conSocket;
                        PrintWriter out;
                        BufferedReader in;
                        print("Input IP/hostname");
                        String ip = input.nextLine();
                        print("Input Port");
                        int serport = input.nextInt();
                        try {
                                conSocket = new Socket(ip, serport);
                                out = new PrintWriter(conSocket.getOutputStream(), true);
                                in = new BufferedReader(new InputStreamReader(conSocket.getInputStream()));
                        } catch (UnknownHostException e) {
                                print("Couldn't find host: " + ip);
                                System.exit(1);
                        } catch (IOException e) {
                                print("Couldn't get I/O for the connection to: " + ip);
                                System.exit(1);
                        }
                        //SocketChannel socket = SocketChannel.open(new InetSocketAddress(ip,serport));
                        print("Connected");
                        ReadableByteChannel source = null;
                        Charset charset = Charset.forName("US-ASCII");
                        CharsetDecoder decoder = charset.newDecoder();
                        ByteBuffer bb = ByteBuffer.allocateDirect(2048);
                        //HERES THE PROBLEM LINE BELOW: THIS ALWAYS RETURNS AN ERROR
                        CharBuffer cb = CharBuffer.allocate(2048);
                        decoder.onMalformedInput(CodingErrorAction.IGNORE);
                        decoder.onUnmappableCharacter(CodingErrorAction.IGNORE);
                        decoder.reset();
                        while(source.read(bb) != -1){
                                bb.flip();
                                decoder.decode(bb, cb, false);
                                cb.flip();
                                System.out.print(cb);
                                cb.clear();
                                bb.compact();
                        }
                }
        }
}

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Thankful for any help!

It is impossible for the indicated line to throw a NullPointerException. All it is doing is calling a static method in the CharBuffer class. copy and paste the full and exact error message.

Quote:

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Originally Posted by Junky

copy and paste the full and exact error message.

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Error on serverside:

Code:

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Exception in thread "main" java.io.IOException: An existing connection was forcibly closed by the remote host
        at sun.nio.ch.SocketDispatcher.write0(Native Method)
        at sun.nio.ch.SocketDispatcher.write(Unknown Source)
        at sun.nio.ch.IOUtil.writeFromNativeBuffer(Unknown Source)
        at sun.nio.ch.IOUtil.write(Unknown Source)
        at sun.nio.ch.SocketChannelImpl.write(Unknown Source)
        at chat.App.startChat(App.java:48)
        at chat.App.<init>(App.java:24)
        at chat.MyChat.main(MyChat.java:9)

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Error on clientside:

Code:

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Exception in thread "main" java.lang.NullPointerException
        at chat.App.startChat(App.java:85)
        at chat.App.<init>(App.java:24)
        at chat.MyChat.main(MyChat.java:9)

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The error message says the exception occured on line 85 which is

Code:

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decoder.decode(bb, cb, false);

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and not the one you claimed. So on that line "decoder", "bb" or "cb" could be false. Add one or more print statements before this line to see which variable is null. Then trace back to see why it is null.

I know its cb. When I place

Code:

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print("doing good")

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in between every line it prints those right up until the line indicated in the first post, which i assume is because it calls cb.


:@: :frusty: :smash:

That is not debugging it correctly. What I meant was try something like:

Code:

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System.out.println("decoder is " + decoder);

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This will identify which of your variables is null. Otherwise you will get something like Classname@hexstring