I am following the Java Trail on networking. The three KnockKnock classes used as examples (client, server, and protocol) work as intended when I copy/paste them into Eclipse. However, what I really want to do is eliminate the protocol class and just have the server echo back to the client whatever I type into the console. I tried modifying the server program mainly by commenting out references to the protocol class, but somehow, I ended up breaking the program.
I am so new that I am clueless as to what is wrong and the more I search for an answer in ebooks and on websites the more confused I get. All I have discovered is that I know next to nothing about how IO streams really work. I pasted all three classes below in the order: server, client, protocol. Where is the problem and why is it a problem:
Server:
import java.net.*;
import java.io.*;
public class KnockKnockServer {
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(4444);
} catch (IOException e) {
System.err.println("Could not listen on port: 4444.");
System.exit(1);
}
Socket clientSocket = null;
try {
clientSocket = serverSocket.accept();
System.out.println("Client Accepted");
} catch (IOException e) {
System.err.println("Accept failed.");
System.exit(1);
}
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(
clientSocket.getInputStream()));
String inputLine, outputLine;
//KnockKnockProtocol kkp = new KnockKnockProtocol();
//outputLine = kkp.processInput(null);
//out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
//outputLine = kkp.processInput(inputLine);
//out.println(outputLine);
out.println(inputLine);
if (inputLine.equals("Bye."))
break;
}
out.close();
in.close();
clientSocket.close();
serverSocket.close();
}
}
Client:
import java.io.*;
import java.net.*;
public class KnockKnockClient {
public static void main(String[] args) throws IOException {
Socket kkSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
kkSocket = new Socket("localhost", 4444);
out = new PrintWriter(kkSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: taranis.");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to: taranis.");
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Bye."))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
out.close();
in.close();
stdIn.close();
kkSocket.close();
}
}
Protocol:
import java.net.*;
import java.io.*;
public class KnockKnockProtocol {
private static final int WAITING = 0;
private static final int SENTKNOCKKNOCK = 1;
private static final int SENTCLUE = 2;
private static final int ANOTHER = 3;
private static final int NUMJOKES = 5;
private int state = WAITING;
private int currentJoke = 0;
private String[] clues = { "Turnip", "Little Old Lady", "Atch", "Who", "Who" };
private String[] answers = { "Turnip the heat, it's cold in here!",
"I didn't know you could yodel!",
"Bless you!",
"Is there an owl in here?",
"Is there an echo in here?" };
public String processInput(String theInput) {
String theOutput = null;
if (state == WAITING) {
theOutput = "Knock! Knock!";
state = SENTKNOCKKNOCK;
} else if (state == SENTKNOCKKNOCK) {
if (theInput.equalsIgnoreCase("Who's there?")) {
theOutput = clues[currentJoke];
state = SENTCLUE;
} else {
theOutput = "You're supposed to say \"Who's there?\"! " +
"Try again. Knock! Knock!";
}
} else if (state == SENTCLUE) {
if (theInput.equalsIgnoreCase(clues[currentJoke] + " who?")) {
theOutput = answers[currentJoke] + " Want another? (y/n)";
state = ANOTHER;
} else {
theOutput = "You're supposed to say \"" +
clues[currentJoke] +
" who?\"" +
"! Try again. Knock! Knock!";
state = SENTKNOCKKNOCK;
}
} else if (state == ANOTHER) {
if (theInput.equalsIgnoreCase("y")) {
theOutput = "Knock! Knock!";
if (currentJoke == (NUMJOKES - 1))
currentJoke = 0;
else
currentJoke++;
state = SENTKNOCKKNOCK;
} else {
theOutput = "Bye.";
state = WAITING;
}
}
return theOutput;
}
}
I think your problem is just both apps are waiting:
when KKServer starts, it waits for a client, and then it's waiting until the client "says" something, and the client is waiting until the server says something before waiting for the user input
Related
I am making 2 classes for Chat server client for a project I am working on. The problem is server can see the message that sent to it(from client) and it can send those messages out to every clients BUT each client has to type in some input first if he wants to see the message from other users. I have no clue what I did wrong. Please help me out. Thanks in advance :)
Server Class
import java.net.*;
import java.util.ArrayList;
import java.io.*;
public class TestServer extends Thread
{
protected Socket clientSocket;
public static ArrayList<Socket> ConnectionArray = new ArrayList<Socket>();
public static ArrayList<String> CurrentUsers = new ArrayList<String>();
final static int PORT = 22;
public static void main(String[] args) throws IOException
{
ServerSocket serverSocket = null;
try
{
serverSocket = new ServerSocket(PORT);
System.out.println ("Connection Socket Created");
try
{
while (true)
{
System.out.println ("Waiting for Connection");
Socket sock = serverSocket.accept();
ConnectionArray.add(sock);
System.out.println("Client connected from: " + sock.getLocalAddress().getHostName());
new TestServer (sock);
}
}
catch (IOException e)
{
System.err.println("Accept failed.");
System.exit(1);
}
}
catch (IOException e)
{
System.err.println("Could not listen on port: " + PORT);
System.exit(1);
}
finally
{
try {
serverSocket.close();
}
catch (IOException e)
{
System.err.println("Could not close port: 10008.");
System.exit(1);
}
}
}
private TestServer (Socket inSock)
{
clientSocket = inSock;
start();
}
public void run()
{
System.out.println ("New Communication Thread Started");
//System.out.println ("Client connected from: " + sock.getLocalAddress().getHostName());
try {
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(),true);
BufferedReader in = new BufferedReader(new InputStreamReader( clientSocket.getInputStream()));
String inputLine;
while (true)
{
inputLine = in.readLine();
System.out.println ("Server: " + inputLine);
for(int i = 1; i <= TestServer.ConnectionArray.size(); i++)
{
System.out.println("Total Connection: " + ConnectionArray.size());
Socket TEMP_SOCK = (Socket) TestServer.ConnectionArray.get(i-1);
if (clientSocket != TEMP_SOCK)
{
PrintWriter TEMP_OUT = new PrintWriter(TEMP_SOCK.getOutputStream(), true);
TEMP_OUT.println(inputLine);
TEMP_OUT.flush();
System.out.println("Sending to: " + TEMP_SOCK.getLocalAddress().getHostName());
}
}
if (inputLine.equals("Bye."))
break;
}
out.close();
in.close();
clientSocket.close();
}
catch (IOException e)
{
System.err.println("Problem with Communication Server");
System.exit(1);
}
}
}
Client Class
import java.io.*;
import java.net.*;
public class TestClient {
public static void main(String[] args) throws IOException {
String serverHostname = new String ("127.0.0.1");
if (args.length > 0)
serverHostname = args[0];
System.out.println ("Attemping to connect to host " +
serverHostname);
Socket echoSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
echoSocket = new Socket(serverHostname, 22);
out = new PrintWriter(echoSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host: " + serverHostname);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for "
+ "the connection to: " + serverHostname);
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String userInput;
System.out.println ("Type Message (\"Bye.\" to quit)");
while ((userInput = stdIn.readLine()) != null)
{
out.println(userInput);
if (userInput.equals("Bye."))
break;
System.out.println("Other user: " + in.readLine());
}
out.close();
in.close();
stdIn.close();
echoSocket.close();
}
}
You need a separate thread in the client for reading from the server without blocking on System.in;
Thread t = new Thread(() -> {
try {
while (!Thread.currentThread().isInterrupted()) {
System.out.println("Other user: " + in.readLine());
}
} catch (Exception e) {
e.printStackTrace();
}
});
t.start();
while ((userInput = stdIn.readLine()) != null)
{
out.println(userInput);
if (userInput.equals("Bye."))
break;
}
t.interrupt();
I'm trying to learn how to use java sockets before next semester. I wrote this program that is supposed to accept accept a message from a sender and send the message to a reciever. You specify the reciever by writing the name of the client that is connected, if the client isn't connected then the server will respond by sending the message "DISCONNECTED". But for some reason the message isn't sent to the reciever. I can still send the message to the sender though. Is this the right forum to ask for this kind of help?
This is my client class
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
public class MyTestClient {
static int port = 0;
static String ip = "";
static String name = "";
public static void main(String args[] ) {
if(args.length == 3) {
try{
port = Integer.parseInt(args[1]);
} catch(NumberFormatException e) {
System.out.println("Usage: Java MyTestClient <ip> <port> <name>");
System.exit(0);
}
ip = args[0];
name = args[2];
} else {
System.out.println("Usage: Java MyTestClient <ip> <port> <name>");
System.exit(0);
}
try {
Socket socket = new Socket(ip, port);
new Thread(new MessageHandler(socket)).start();
new Thread(new InputHandler(socket)).start();
} catch (IOException e) {
System.out.println("Could not connect to: " + ip + " : " + port);
System.exit(0);
}
}
public static class MessageHandler implements Runnable {
Socket socket;
public MessageHandler(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
PrintWriter out = null;
BufferedReader in = null;
try {
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
}catch(IOException e) {
e.printStackTrace();
}
String fromServer;
try {
while ((fromServer = in.readLine()) != null) {
System.out.println(fromServer);
fromServer.trim();
if(fromServer.contains(" ")) {
String split[] = fromServer.split(" ", 2);
System.out.println(split.length == 2 ? split[1] + " Is a two part message" : "Strange message");
} else {
if(fromServer.equals("NAME")) {
System.out.println("Server asks for name | gives given name to server");
out.println(name);
}
if(fromServer.equals("SUCCESS")) {
System.out.println("Message succesfully sent");
}
if(fromServer.equals("ERROR")) {
System.out.println("Something went wrong when sending the message");
}
if(fromServer.equals("OCCUPIED")) {
System.out.println("Name was already used. Start the program with another name");
socket.close();
System.exit(0);
}
if(fromServer.equals("DISCONNECTED")) {
System.out.println("The reciever was not connected");
}
if(fromServer.equals("REGISTERED")) {
System.out.println("Successfully logged in to server");
}
}
}
} catch(IOException e) {
e.printStackTrace();
}
}
}
public static class InputHandler implements Runnable {
Socket socket;
public InputHandler(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
String fromUser = null;
PrintWriter out = null;
try {
out = new PrintWriter(socket.getOutputStream(), true);
} catch (IOException e) {
e.printStackTrace();
}
BufferedReader kbi = new BufferedReader(new InputStreamReader(System.in));
try {
while ((fromUser = kbi.readLine()) != null) {
out.println(fromUser);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
This is my server class
import java.io.*;
import java.net.*;
import java.util.*;
public class MyServer {
public static int port;
public static int maxConnections;
public static final String NAME = "Server";
private static Map<String, Socket> socketsMap = new HashMap<>();
public static void main(String args[]) {
if(args.length == 2) {
try{
port = Integer.parseInt(args[0]);
maxConnections = Integer.parseInt(args[1]);
}catch(Exception e){
System.out.println("Usage: Java Myserver <port> <maxConnections>");
System.exit(0);
}
} else {
System.out.println("Usage: Java Myserver <port> <maxConnections>");
System.exit(0);
}
new Thread(new ConnectionHandler(port, maxConnections)).start();
}
public static class ConnectionHandler implements Runnable {
private ServerSocket server;
private Socket socket = null;
public int currentSocket = 0;
public int port = 0;
public int maxConnections = 0;
public ConnectionHandler(int port, int maxConnections) {
this.maxConnections = maxConnections;
this.port = port;
}
#Override
public void run() {
try {
server = new ServerSocket(7777);
} catch (IOException e1) {
System.out.println("Server could not connect to port: " + port);
e1.printStackTrace();
System.exit(0);
}
while(currentSocket++ < maxConnections) {
try {
socket = server.accept();
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
out.println("NAME");
String message;
while((message = in.readLine()) != null) {
if(!socketsMap.containsKey(message) || message.equals("SERVER")) {
out.println("REGISTERED");
socketsMap.put(message, socket);
System.out.println(message + " has logged on server");
new Thread(new SocketHandler(socketsMap.get(message))).start();
} else {
out.println("OCCUPIED");
System.out.println(socket.getInetAddress().toString() + " has tried to login with existing name " + message);
socket.close();
currentSocket--;
}
socket = null;
break;
}
} catch (IOException e) {
System.out.println("Something went wrong with client connection");
}
}
}
}
public static class SocketHandler implements Runnable {
Socket socket = null;
public SocketHandler(Socket socket) {
this.socket = socket;
}
#Override
public void run() {
try {
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
PrintWriter respond = new PrintWriter(socket.getOutputStream(), true);
String input;
while((input = in.readLine() ) != null) {
String[] info = input.split(" ", 2);
if(info.length != 2){
System.out.println("Message computed wrong");
respond.println("ERROR");
break;
}
if(info[0].equals("SERVER")) {
//TODO: Write a server command handler class
} else if ( socketsMap.containsKey(info[0]) ){
Socket reciever = socketsMap.get(info[0]);
PrintWriter out = new PrintWriter(reciever.getOutputStream());
respond.println("SUCCESS");
System.out.println(info[0] + " send the message: "+ info[1]);
out.println("MESSAGE" + " " + info[1]);
break;
} else {
System.out.println("Reciever is not connected");
respond.println("DISCONNECTED");
}
}
}catch(IOException e) {
e.printStackTrace();
}
}
}
}
Maybe you can run it on your computers and see what i mean?
#Override
public void run() {
try {
server = new ServerSocket(7777);
} catch (IOException e1) {
System.out.println("Server could not connect to port: " + port);
e1.printStackTrace();
System.exit(0);
}
change the code above to
#Override
public void run() {
try {
server = new ServerSocket(port);
} catch (IOException e1) {
System.out.println("Server could not connect to port: " + port);
e1.printStackTrace();
System.exit(0);
}
Very confused, I just posted this question but deleted it because I made many mistakes. Alright well here goes again! I have a server program in java below. When I run it I expect to see some sort of presence in netstat, but I see nothing. Here are some screen shots:
Before running server: https://www.dropbox.com/s/upo9ndbzuxbk9j1/Screenshot%202014-12-24%2002.25.49.png?dl=0
After running server (server running in top right terminal, bottom right is client and obviously left is netstat): https://www.dropbox.com/s/05urjvz3lskvzkc/Screenshot%202014-12-24%2002.28.24.png?dl=0
Somewhat long but here is the server (I run it with 63400):
import java.net.*;
import java.io.*;
public class JavaTest2 {
public static void main(String[] args) throws IOException {
if (args.length != 1) {
System.err.println("Usage: java KnockKnockServer <port number>");
System.exit(1);
}
int portNumber = Integer.parseInt(args[0]);
try (
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
) {
String inputLine, outputLine;
// Initiate conversation with client
KnockKnockProtocol kkp = new KnockKnockProtocol();
outputLine = kkp.processInput(null);
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye."))
break;
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
}
}
}
class KnockKnockProtocol {
private static final int WAITING = 0;
private static final int SENTKNOCKKNOCK = 1;
private static final int SENTCLUE = 2;
private static final int ANOTHER = 3;
private static final int NUMJOKES = 5;
private int state = WAITING;
private int currentJoke = 0;
private String[] clues = { "Turnip", "Little Old Lady", "Atch", "Who", "Who" };
private String[] answers = { "Turnip the heat, it's cold in here!",
"I didn't know you could yodel!",
"Bless you!",
"Is there an owl in here?",
"Is there an echo in here?" };
public String processInput(String theInput) {
String theOutput = null;
if (state == WAITING) {
theOutput = "Knock! Knock!";
state = SENTKNOCKKNOCK;
} else if (state == SENTKNOCKKNOCK) {
if (theInput.equalsIgnoreCase("Who's there?")) {
theOutput = clues[currentJoke];
state = SENTCLUE;
} else {
theOutput = "You're supposed to say \"Who's there?\"! " +
"Try again. Knock! Knock!";
}
} else if (state == SENTCLUE) {
if (theInput.equalsIgnoreCase(clues[currentJoke] + " who?")) {
theOutput = answers[currentJoke] + " Want another? (y/n)";
state = ANOTHER;
} else {
theOutput = "You're supposed to say \"" +
clues[currentJoke] +
" who?\"" +
"! Try again. Knock! Knock!";
state = SENTKNOCKKNOCK;
}
} else if (state == ANOTHER) {
if (theInput.equalsIgnoreCase("y")) {
theOutput = "Knock! Knock!";
if (currentJoke == (NUMJOKES - 1))
currentJoke = 0;
else
currentJoke++;
state = SENTKNOCKKNOCK;
} else {
theOutput = "Bye.";
state = WAITING;
}
}
return theOutput;
}
}
Now when I run the client I can see the presence in netstat at the very top, the two sockets as my server and client running on same computer. But still no server socket :(
Screenshot: https://www.dropbox.com/s/bnrbyk41mjob5bg/Screenshot%202014-12-24%2002.25.53.png?dl=0
Code for client (ran with 127.0.0.1 64300):
import java.io.*;
import java.net.*;
public class JavaTest {
public static void main(String[] args) throws IOException {
if (args.length != 2) {
System.err.println(
"Usage: java KnockKnockClient <host name> <port number>");
System.exit(1);
}
String hostName = args[0];
int portNumber = Integer.parseInt(args[1]);
try (
Socket kkSocket = new Socket(hostName, portNumber);
PrintWriter out = new PrintWriter(kkSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(kkSocket.getInputStream()));
) {
BufferedReader stdIn =
new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("Bye."))
break;
fromUser = stdIn.readLine();
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}
Thanks in advance to anyone who takes the time to figure it out!
I think it may just be netstat but I still want to know why as when I run lsof -i :64300
it shows my java process, when only the server is running. And when I run that with everything I see 3 (as you can see in the left terminal in this screenshot https://www.dropbox.com/s/1focc9dmhkidtan/Screenshot%202014-12-24%2002.52.22.png?dl=0). I cancel the netstat after it shows me what I "think" is relevant because I cannot interpret the rest. I dont know if its there. Hopefully someone helps!
Ok I am just finding out more as I write this cause I cannot post for 90 minutes but, now when I use intellij idea and run it there. Just the server, there is no change, but when I add the client I see everything!
before anything: https://www.dropbox.com/s/akupewmprcld0b3/Screenshot%202014-12-24%2002.59.05.png?dl=0
server: https://www.dropbox.com/s/uvxmz0jvjozbkyy/Screenshot%202014-12-24%2002.59.34.png?dl=0
client + server: https://www.dropbox.com/s/bssa16s1n3adwdq/Screenshot%202014-12-24%2003.00.00.png?dl=0
What is going on.... I also see 6 localhosts instead of 3... God this is interesting or I am just making one very silly mistake. But I am starting to doubt any of this matters.
netstat omits listening sockets by default. There's an -l option or -all for all sockets. – laune
I"m working on a Client-Server chat program for a university project and I have little programming background. I've made 3 classes: ChatClient, ChatServer and ChatServerThread. I can currently have multiple clients connected and talking to the server at any time.
Although one of the requirements that I'm having the most difficulty is this: "Any message typed from 1 client is sent to all other clients" and also "Both sent and received messages should be displayed".
I've spent the last few nights just trying to get this extra bit of functionality working but have had no luck.
I've been reading and looking around for a while but I have lots of difficulty adapting online examples to my work. I've read that I should be creating a list of sockets and then iterate through the list and send data to everyone in the list, which makes sense in my head but gives me a headache when I try implementing it. Any help with this would be very greatly appreciated. Extra points if anyone can give me some insight on how I could encrypt the sent data.
ChatClient
import java.net.*;
import java.io.*;
public class ChatClient {
private Socket socket = null;
private DataInputStream console = null;
private DataOutputStream streamOut = null;
private String myName = null;
private BufferedReader StreamIn = null;
private String response = null;
public ChatClient(String serverName, int serverPort) {
try {
console = new DataInputStream(System.in);
System.out.println("What is your name?");
myName = console.readLine();
System.out.println(myName + " <" + InetAddress.getLocalHost() + "> ");
} catch (IOException ioe) {
System.out.println("Unexpected exception: " + ioe.getMessage());
}
System.out.println("Establishing connection. Please wait ...");
try {
socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
StreamIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
streamOut = new DataOutputStream(socket.getOutputStream());
streamOut.writeUTF(":" + myName + " <" + InetAddress.getLocalHost() + "> HAS JOINED");
streamOut.flush();
} catch (UnknownHostException uhe) {
System.out.println("Host unknown: " + uhe.getMessage());
} catch (IOException ioe) {
System.out.println("Unexpected exception: " + ioe.getMessage());
}
String line = "";
while (!line.equals(".bye")) {
try {
line = console.readLine();
streamOut.writeUTF(myName + " <" + InetAddress.getLocalHost() + "> : " + line);
streamOut.flush();
} catch (IOException ioe) {
System.out.println("Sending error: " + ioe.getMessage());
}
}
}
public void stop() {
try {
if (console != null) console.close();
if (streamOut != null) streamOut.close();
if (socket != null) socket.close();
} catch (IOException ioe) {
System.out.println("Error closing ...");
}
}
public static void main(String args[]) {
ChatClient client = null;
if (args.length != 2)
System.out.println("Usage: java ChatClient host port");
else
client = new ChatClient(args[0], Integer.parseInt(args[1]));
}
}
ChatServer
import java.net.*;
import java.io.*;
import java.util.*;
public class ChatServer implements Runnable {
private ServerSocket server = null;
private Thread thread = null;
private ChatServerThread client = null;
private String clientSentence = null;
private int peers = 0;
private List clients = new ArrayList();
final List sockets = new ArrayList();
public ChatServer(int port) {
try {
System.out.println("Binding to port " + port + ", please wait ...");
server = new ServerSocket(port);
System.out.println("Server started: " + server);
start();
} catch (IOException ioe) {
System.out.println(ioe);
}
}
public void run() {
while (thread != null) {
try {
System.out.println("Waiting for a client ...");
addThread(server.accept());
} catch (IOException ie) {
System.out.println("Acceptance Error: " + ie);
}
}
}
public void addThread(Socket socket) {
System.out.println("Client accepted: " + socket);
client = new ChatServerThread(this, socket);
try {
client.open();
client.start();
} catch (IOException ioe) {
System.out.println("Error opening thread: " + ioe);
}
}
public void start() {
if (thread == null) {
thread = new Thread(this);
thread.start();
}
}
public void stop() {
if (thread != null) {
thread.stop();
thread = null;
}
}
public void increment(String sentence) {
peers++;
String[] info = sentence.split(" ");
String name = info[0].replace(":", "");
System.out.println(name + " Has joined the room, we now have " + peers + " peer(s).");
clients.add(name);
}
public Boolean isAllowed(String name, Socket socket) {
try {
String stringSearch = name;
BufferedReader bf = new BufferedReader(new FileReader("allowed.txt"));
int linecount = 0;
String line = "";
System.out.println("Searching for " + stringSearch + " in file...");
while ((line = bf.readLine()) != null) {
linecount++;
String[] words = line.split(" ");
for (String word : words) {
if (word.equals(stringSearch)) {
System.out.println("User is allowed");
registerSocket(socket);
return true;
}
}
}
bf.close();
} catch (IOException e) {
System.out.println("IO Error Occurred: " + e.toString());
}
System.out.println("User is not allowed");
return false;
}
public void showAll() {
for (int i = 0; i < clients.size(); i++) {
System.out.print(clients.get(i));
}
}
public void registerSocket(Socket socket) {
//socket = new DataOutputStream(socket.getOutputStream());
sockets.add(socket);
for (int i = 0; i < sockets.size(); i++) {
System.out.println(sockets.get(i));
}
}
public static void main(String args[]) {
ChatServer server = null;
if (args.length != 1)
System.out.println("Usage: java ChatServer port");
else
server = new ChatServer(Integer.parseInt(args[0]));
}
}
ChatServerThread
import java.net.*;
import java.io.*;
public class ChatServerThread extends Thread {
private Socket socket = null;
private ChatServer server = null;
private int ID = -1;
private DataInputStream streamIn = null;
private String clientSentence = null;
public String newGuy = null;
DataOutputStream streamOut = null;
public ChatServerThread(ChatServer _server, Socket _socket) {
server = _server;
socket = _socket;
ID = socket.getPort();
}
public void run() {
System.out.println("Server Thread " + ID + " running.");
while (true) {
try {
String sentence = streamIn.readUTF();
//System.out.println(sentence);
char c = sentence.charAt(0);
String[] command = null;
command = sentence.split(" ");
String name = command[0].substring(1);
System.out.println("Sending out: " + sentence + " via ");
streamOut.writeBytes(sentence);
if (c == ':') {
if (server.isAllowed(name, socket))
server.increment(sentence);
else {
close();
}
}
} catch (IOException ioe) {
}
}
}
public void open() throws IOException {
streamIn = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
}
public void close() throws IOException {
if (socket != null) socket.close();
if (streamIn != null) streamIn.close();
}
}
I am working on a simple server in Java that should have a capability of transferring a file across computers. I am getting a NullPointerException on line 77 of Protocol.class. Here is the stack:
java.lang.NullPointerException
at Protocol.processInput(Protocol.java:77)
at Server.main(Server.java:41)
Why does this happen? There is no null references on line 77!
Client.java:
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;
import javax.swing.JFileChooser;
import javax.swing.JOptionPane;
import javax.swing.filechooser.FileNameExtensionFilter;
public class Client {
private static boolean filein = false;
private static ArrayList<String> fln = new ArrayList<>();
public static void main(String[] args) throws IOException {
if (args.length != 2) {
System.err.println(
"Usage: java Client <host name> <port number>");
System.exit(1);
}
String hostName = args[0];
int portNumber = Integer.parseInt(args[1]);
try (
Socket kkSocket = new Socket(hostName, portNumber);
PrintWriter out = new PrintWriter(kkSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(kkSocket.getInputStream()));
) {
BufferedReader stdIn =
new BufferedReader(new InputStreamReader(System.in));
String fromServer;
String fromUser = null;
while ((fromServer = in.readLine()) != null) {
System.out.println("Server: " + fromServer);
if (fromServer.equals("#file")) { filein = true;
fromUser = "";}
else if(fromServer.equals("#end#")) {
filein = false;
JFileChooser chooser = new JFileChooser();
int returnVal = chooser.showSaveDialog(null);
if(returnVal == JFileChooser.APPROVE_OPTION) {
String fname = chooser.getSelectedFile().getAbsolutePath();
File f = new File(fname);
f.createNewFile();
PrintWriter p = new PrintWriter(f);
for(int i = 0; i < fln.size(); i++) {
p.println(fln.get(i));
}
p.close();
JOptionPane.showMessageDialog(null, "File saved!");
}
}
else if (filein == true) {
fln.add(fromServer);
System.out.println(fln.get(fln.size() - 1));
}
if (fromServer.equals("Bye."))
break;
if (!filein) fromUser = stdIn.readLine();
else if (filein) fromUser = "#contintueFileRun";
if (fromUser != null) {
System.out.println("Client: " + fromUser);
out.println(fromUser);
}
}
} catch (UnknownHostException e) {
System.err.println("Don't know about host " + hostName);
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection to " +
hostName);
System.exit(1);
}
}
}
Server.java:
import java.io.*;
import java.net.*;
import static java.lang.System.out;
/**
* Title: FTP Server
* #author Galen Nare
* #version 1.0
*/
public class Server {
public static void main(String[] args) throws IOException {
out.println("Starting server!");
if (args.length != 1) {
System.err.println("Usage: java Server <port number>");
System.exit(1);
}
int portNumber = Integer.parseInt(args[0]);
try (
ServerSocket serverSocket = new ServerSocket(portNumber);
Socket clientSocket = serverSocket.accept();
PrintWriter out =
new PrintWriter(clientSocket.getOutputStream(), true);
BufferedReader in = new BufferedReader(
new InputStreamReader(clientSocket.getInputStream()));
) {
String inputLine, outputLine;
// Initiate conversation with client
Protocol kkp = new Protocol();
outputLine = kkp.processInput("");
out.println(outputLine);
while ((inputLine = in.readLine()) != null) {
outputLine = kkp.processInput(inputLine);
out.println(outputLine);
if (outputLine.equals("Bye."))
break;
}
} catch (IOException e) {
System.out.println("Exception caught when trying to listen on port "
+ portNumber + " or listening for a connection");
System.out.println(e.getMessage());
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
And finally, Protocol.java:
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Scanner;
public class Protocol {
enum ServerState {
STARTING,
WAITING
}
ArrayList<String> lns;
boolean fileout = false;
int i = 0;
private ServerState state = ServerState.STARTING;
public String processInput(String theInput) throws Exception {
String theOutput = "";
if (state == ServerState.STARTING) {
theOutput = "Hello, Client!";
state = ServerState.WAITING;
}
if (!theInput.equals("")) {
if(theInput.length() > 10 && theInput.startsWith("e")) {
if (theInput.substring(0,11).equalsIgnoreCase("executecmd ")) {
theOutput = theInput.substring(11);
System.out.println(theOutput);
try {
#SuppressWarnings("unused")
Process child = Runtime.getRuntime().exec(theInput.substring(11));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
theOutput = "Executed " + theInput.substring(11) + ".";
}
} else if (theInput.equalsIgnoreCase("stop")) {
theOutput = "Stopping Server!";
System.exit(0);
} else if (theInput.equalsIgnoreCase("executecmd")) {
theOutput = "Usage: executecmd <command [-options]>";
} else if (theInput.equalsIgnoreCase("getfile")) {
theOutput = "Usage: getfile <file>";
} else if(theInput.length() > 7 && theInput.startsWith("g")) {
System.out.println("in");
if (theInput.substring(0,8).equalsIgnoreCase("getfile ")) {
theOutput = theInput.substring(8);
File f = new File(theInput.substring(8));
Scanner scan = new Scanner(f);
ArrayList<String> lns = new ArrayList<>();
while(scan.hasNext()) {
lns.add(scan.nextLine());
}
for (int i=0; i < lns.size(); i++) {
System.out.println(lns.get(i));
}
scan.close();
lns.add("#end#");
theOutput = "#file";
fileout = true;
}
} else if (fileout && i < lns.size()) {
theOutput = lns.get(i);
i++;
} else if (fileout && i == lns.size()) {
i = 0;
fileout = false;
} else {
theOutput = "That is not a command!";
}
}
System.out.print(theOutput);
return theOutput;
}
}
Thanks in advance!
You're never initializing lns in Protocol, so it's always a null reference. You may be able to get away with just changing the declaration to:
private List<String> lns = new ArrayList<String>();
(I've made it private and changed the type to List just out of habit...)
You should also consider giving it a more readable name - is it meant to represent lines? If so, call it lines!
(Next, consider why you weren't able to diagnose this yourself. Did you step through this in the debugger? Why did you think there were no null references on line 77? What diagnostic steps did you take in terms of adding extra logging etc? It's important to use errors like this as a learning experience to make future issues more tractable.)