Develop Reference

UnknownHostException in Java Client/Server-Programm

The class Server:
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class Server{
private int port;
private Socket client;
private ServerSocket server;
public Server(int port) {
try {
this.port = port;
setServer(new ServerSocket(this.port));
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
this.start();
}
public void start() {
ArrayList<ClientHandler> clients = new ArrayList<>();
ExecutorService executor = Executors.newFixedThreadPool(20);
System.out.println("Server started...");
while (true) {
try {
setClient(null);
setClient(getServer().accept());
if (getClient() != null) {
ClientHandler handler = new ClientHandler(getClient());
System.out.println("Client connected...");
clients.add(handler);
executor.execute(handler);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void main(String[] args) {
Server server = new Server(4567);
}
public Socket getClient() {
return client;
}
public void setClient(Socket client) {
this.client = client;
}
public ServerSocket getServer() {
return server;
}
public void setServer(ServerSocket server) {
this.server = server;
}
}
Now, my Question is, is there a Problem in the class, which causes the UnknownHostException? I already tried to debug, but the problem lies in the class Client
The Class Client:
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.util.Scanner;
public class Client{
private String kennung;
private Socket server;
private String host;
private int port;
public Client(String kennung, String host, int port){
setKennung(kennung);
setHost(host);
setPort(port);
try {
setServer(new Socket(this.host, this.port));
//Scanner reader = new Scanner(this.server.getInputStream());
PrintWriter writer = new PrintWriter(getServer().getOutputStream(), true);
Scanner sc = new Scanner(System.in);
writer.println("The Client");
/*while(true){
boolean next = reader.hasNext();
if (next) {
String line = reader.nextLine();
if(!line.equals(null)){
System.out.println("From another one: " + line);
}
}
writer.println(sc.next());
}*/
} catch (UnknownHostException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if( server != null){
try {
server.close();
} catch (IOException e) {
//ignore -> Server getting closed
}
}
}
}
public String getKennung() {
return kennung;
}
public void setKennung(String kennung) {
this.kennung = kennung;
}
public Socket getServer() {
return server;
}
public void setServer(Socket server) {
this.server = server;
}
public String getHost() {
return host;
}
public void setHost(String host) {
this.host = host;
}
public int getPort() {
return port;
}
public void setPort(int port) {
this.port = port;
}
public static void main(String[] args) {
Client testClient = new Client("testClient", "127.0.0.1", 4567);
System.out.println("Client created");
}
}
And Last, but not least: The Class ClientHandler that implements Runnable and runs a Thread, where I read the input from the client and write it to the server.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.concurrent.ArrayBlockingQueue;
public class ClientHandler implements Runnable {
public ArrayBlockingQueue<String> messsages;
Socket client;
public ClientHandler(Socket client) {
this.messsages = new ArrayBlockingQueue<>(20);
this.client = client;
}
#Override
public void run() {
PrintWriter writer = null;
Scanner reader = null;
try {
reader = new Scanner(this.client.getInputStream());
writer = new PrintWriter(this.client.getOutputStream(), true);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
String line = "";
while (!line.equals(".bye")) {
//System.out.println("Got something? " + reader.hasNext());
line = reader.nextLine();
if (reader.hasNext()) {
if (!line.equals(null)) {
System.out.println("Vom Client: " + line);
}
}
//writer.println("Admin-Message"); // Zum Testen
}
}
}
Thanks to everybody, who helps me with this problem.

HttpSession getAttribute() returning null

I'm trying to do a websocket communication with eclipse ide and when i run my code i get a NullPointerException. I've checked and the name in the getAttribute is the same as in the bean
package ws;
import java.io.IOException;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import javax.websocket.server.ServerEndpoint;
import fundstarter.model.ConnectToRMIBean;
import javax.servlet.http.HttpSession;
import javax.websocket.*;
#ServerEndpoint(value="/ws", configurator = HandShake.class)
public class WebSocketAnnotation {
private Session session;
private ConnectToRMIBean sessionUser;
private HttpSession httpSession;
private static final Set<WebSocketAnnotation> myConnections = new CopyOnWriteArraySet<WebSocketAnnotation>();
public WebSocketAnnotation() {
}
#OnOpen
public void start(Session session, EndpointConfig config) {
this.session = session;
this.httpSession = (HttpSession) config.getUserProperties().get(HttpSession.class.getName());
myConnections.add(this);
this.sessionUser = (ConnectToRMIBean) httpSession.getAttribute("RMIBean");
//sendMessage("New message");
}
#OnClose
public void end() {
// clean up once the WebSocket connection is closed
myConnections.remove(this);
}
#OnMessage
public void receiveMessage(String message) {
sendMessage(message);
}
#OnError
public void handleError(Throwable t) {
t.printStackTrace();
}
private void sendMessage(String text) {
try {
System.out.println("[WebSocketAnnot]RMIBean User Id -> " + this.sessionUser.getUserID());
this.session.getBasicRemote().sendText(text);
} catch (IOException e) {
try {
this.session.close();
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
Can anyone tell me what is my error?

I found the error. It was a typo on the modifyHandshake method on the HandShake

Close websocket connection with Java

How to close a websocket connection using Java WebSocket API? I have used Java websocket API for both server and client end points. The application is working fine. But I don't know how to close the websocket, before the main thread ends.
This is my ClientEndpoint
package websocket.client;
import java.io.IOException;
import javax.websocket.MessageHandler;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
#ClientEndpoint
public class EchoClient {
Session session;
//request
#OnOpen
public void onOpen(Session session, EndpointConfig config) {
System.out.println("Connected to endpoint: " + session.getBasicRemote());
this.session = session;
sendMessage("Welcome to WebSocket");
}
//response
#OnMessage
public void onMessage(String text) {
System.out.println("Received response in client from server: " + text);
}
#OnError
public void onError(Session session, Throwable t) {
t.printStackTrace();
}
private void sendMessage(String message) {
System.out.println("Sending message from client to server: " + message);
System.out.println(session);
try {
session.getBasicRemote().sendText(message);
} catch (IOException e) {
e.printStackTrace();
}
}
}
And I use the following code to start the ClientEndPoint
import java.io.IOException;
import java.net.URI;
import javax.websocket.ContainerProvider;
import javax.websocket.DeploymentException;
import javax.websocket.WebSocketContainer;
import websocket.client.EchoClient;
public class WebSocketDemo {
public static void main(String[] args) {
String uri = "ws://localhost:8080/websocket";
System.out.println("Connecting to " + uri);
WebSocketContainer container = ContainerProvider.getWebSocketContainer();
try {
container.connectToServer(EchoClient.class, URI.create(uri));
} catch (DeploymentException | IOException e) {
e.printStackTrace();
}
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
PS : I haven't used JavaScript.

The WebSocketContainer's connectToServer method returns websocket Session object that has two close methods. That should do the trick.

My simple Java NIO client server non-blocking connection does not work

I'm trying to play around with a simple client-server program, eventually aiming to make it a two-way communication. For some reason when I just instantiate the client class to make it connect to the server (without sending any data), it doesn't work, and throws Unable to establish loopback connection exception. When I put a while loop of reading through stdin, it works then. I need to establish a connection first, and then once in a while send a message to the server. How can I fix it?
Client code:
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
public class ClientCore {
SelectionKey selkey;
Selector sckt_manager ;
SocketChannel sc;
public ClientCore() {
try {
sc = SocketChannel.open();
sc.configureBlocking(false);
sc.connect(new InetSocketAddress(8888));
// should not proceed until connect is finished
while (!sc.finishConnect()) {
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (sc != null) {
try {
sc.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
void send(String message) {
try {
if (!message.equalsIgnoreCase("end")) {
System.out.println("Sending a request to the server ...");
ByteBuffer buffer = ByteBuffer.wrap(message.getBytes());
sc.write(buffer);
}
} catch (IOException e) {
}
}
public static void main(String[] args) throws Exception {
ClientCore cl = new ClientCore();
cl.send("hello");
}
}
Server code:
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.WritableByteChannel;
import java.nio.channels.spi.SelectorProvider;
public class ServerCore extends Thread {
SelectionKey selkey = null;
Selector sckt_manager = null;
public void run() {
try {
coreServer();
} catch (Exception ej) {
ej.printStackTrace();
}
}
private void coreServer() {
try {
ServerSocketChannel ssc = ServerSocketChannel.open();
try {
ssc.socket().bind(new InetSocketAddress(8888));
while (true) {
sckt_manager = SelectorProvider.provider().openSelector();
ssc.configureBlocking(false);
SocketChannel sc = ssc.accept();
register_server(ssc, SelectionKey.OP_ACCEPT);
if (sc == null) {
} else {
System.out
.println("Received an incoming connection from "
+ sc.socket().getRemoteSocketAddress());
printRequest(sc);
System.err.println("testing 1");
String HELLO_REPLY = "Sample Display";
ByteBuffer buffer = ByteBuffer.wrap(HELLO_REPLY .getBytes());
System.err.println("testing 2");
sc.write(buffer);
System.err.println("testing 3");
sc.close();
}
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (ssc != null) {
try {
ssc.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
} catch (Exception E) {
System.out.println("Ex in servCORE " + E);
}
}
private static void printRequest(SocketChannel sc) throws IOException {
ReadableByteChannel rbc = Channels.newChannel(sc.socket()
.getInputStream());
WritableByteChannel wbc = Channels.newChannel(System.out);
ByteBuffer b = ByteBuffer.allocate(1024); // read 1024 bytes
while (rbc.read(b) != -1) {
b.flip();
while (b.hasRemaining()) {
wbc.write(b);
System.out.println();
}
b.clear();
}
}
public void register_server(ServerSocketChannel ssc, int selectionkey_ops)
throws Exception {
ssc.register(sckt_manager, selectionkey_ops);
}
public static void main(String[] args) {
ServerCore st = new ServerCore();
st.coreServer();
}
}

Tomcat WebSocket connection closed, Code: 1006 issue

I'm trying Tomcat server with websocket. This is what I do:
I created 3 java files, copied from Tomcat examples. Please see the code below.
Then I build a war file and put it in webapps. But then I got this error message:
Info: WebSocket connection closed, Code: 1006
Do I miss any step to make a websocket on Tomcat?
Thanks.
1. ExamplesConfig.java
import java.util.HashSet;
import java.util.Set;
import javax.websocket.Endpoint;
import javax.websocket.server.ServerApplicationConfig;
import javax.websocket.server.ServerEndpointConfig;
public class ExamplesConfig implements ServerApplicationConfig
{
#Override
public Set<ServerEndpointConfig> getEndpointConfigs(Set<Class<? extends Endpoint>> scanned)
{
Set<ServerEndpointConfig> result = new HashSet<ServerEndpointConfig>();
System.out.println("ExamplesConfig ==========> getEndpointConfigs");
if (scanned.contains(EchoEndpoint.class))
{
result.add(ServerEndpointConfig.Builder.create(EchoEndpoint.class, "/websocket/echoProgrammatic").build());
}
return result;
}
#Override
public Set<Class<?>> getAnnotatedEndpointClasses(Set<Class<?>> scanned)
{
// Deploy all WebSocket endpoints defined by annotations in the examples
// web application. Filter out all others to avoid issues when running
// tests on Gump
Set<Class<?>> results = new HashSet<Class<?>>();
for (Class<?> clazz : scanned)
{
if (clazz.getPackage().getName().startsWith("websocket."))
{
System.out.println("getAnnotatedEndpointClasses ===========>" + clazz);
results.add(clazz);
}
}
return results;
}
}
2. EchoEndpoint.java
import java.io.IOException;
import java.nio.ByteBuffer;
import javax.websocket.Endpoint;
import javax.websocket.EndpointConfig;
import javax.websocket.MessageHandler;
import javax.websocket.RemoteEndpoint;
import javax.websocket.Session;
public class EchoEndpoint extends Endpoint
{
#Override
public void onOpen(Session session, EndpointConfig endpointConfig) {
RemoteEndpoint.Basic remoteEndpointBasic = session.getBasicRemote();
session.addMessageHandler(new EchoMessageHandlerText(remoteEndpointBasic));
session.addMessageHandler(new EchoMessageHandlerBinary(remoteEndpointBasic));
}
private static class EchoMessageHandlerText
implements MessageHandler.Partial<String> {
private final RemoteEndpoint.Basic remoteEndpointBasic;
private EchoMessageHandlerText(RemoteEndpoint.Basic remoteEndpointBasic) {
this.remoteEndpointBasic = remoteEndpointBasic;
}
#Override
public void onMessage(String message, boolean last) {
try {
if (remoteEndpointBasic != null) {
remoteEndpointBasic.sendText(message, last);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
private static class EchoMessageHandlerBinary
implements MessageHandler.Partial<ByteBuffer> {
private final RemoteEndpoint.Basic remoteEndpointBasic;
private EchoMessageHandlerBinary(RemoteEndpoint.Basic remoteEndpointBasic) {
this.remoteEndpointBasic = remoteEndpointBasic;
}
#Override
public void onMessage(ByteBuffer message, boolean last) {
try {
if (remoteEndpointBasic != null) {
remoteEndpointBasic.sendBinary(message, last);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
3. EchoAnnotation.java
import java.io.IOException;
import java.nio.ByteBuffer;
import javax.websocket.OnMessage;
import javax.websocket.PongMessage;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
#ServerEndpoint("/websocket/echoAnnotation")
public class EchoAnnotation
{
#OnMessage
public void echoTextMessage(Session session, String msg, boolean last) {
try {
if (session.isOpen()) {
System.out.println("==========> this is my code");
session.getBasicRemote().sendText(msg, last);
}
} catch (IOException e) {
try {
session.close();
} catch (IOException e1) {
// Ignore
}
}
}
#OnMessage
public void echoBinaryMessage(Session session, ByteBuffer bb,
boolean last) {
try {
if (session.isOpen()) {
session.getBasicRemote().sendBinary(bb, last);
}
} catch (IOException e) {
try {
session.close();
} catch (IOException e1) {
// Ignore
}
}
}
/**
* Process a received pong. This is a NO-OP.
*
* #param pm Ignored.
*/
#OnMessage
public void echoPongMessage(PongMessage pm) {
// NO-OP
}
}

This example work's fine with Tomcat 7.0.x if you are running JVM version 1.7 and your web.xml use Servlet Specification version 3.0 according to Tomcat documentation.
You web.xml file should look like this :
<web-app version="3.0" ... >