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chitan / WsChatServlet.java
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How to use WebSocket of Tomcat

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WsChatServlet.java
Java
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//This sample is how to use websocket of Tomcat.
package wsapp;
 
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.util.ArrayList;
import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;
import org.apache.catalina.websocket.WsOutbound;
 
public class WsChatServlet extends WebSocketServlet{
    private static final long serialVersionUID = 1L;
    private static ArrayList<MyMessageInbound> mmiList = new ArrayList<MyMessageInbound>();
 
    public StreamInbound createWebSocketInbound(String protocol){
        return new MyMessageInbound();
    }
 
    private class MyMessageInbound extends MessageInbound{
        WsOutbound myoutbound;
 
        @Override
        public void onOpen(WsOutbound outbound){
            try {
                System.out.println("Open Client.");
                this.myoutbound = outbound;
                mmiList.add(this);
                outbound.writeTextMessage(CharBuffer.wrap("Hello!"));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
 
        @Override
        public void onClose(int status){
            System.out.println("Close Client.");
            mmiList.remove(this);
        }
 
        @Override
        public void onTextMessage(CharBuffer cb) throws IOException{
            System.out.println("Accept Message : "+ cb);
            for(MyMessageInbound mmib: mmiList){
                CharBuffer buffer = CharBuffer.wrap(cb);
                mmib.myoutbound.writeTextMessage(buffer);
                mmib.myoutbound.flush();
            }
        }
 
        @Override
        public void onBinaryMessage(ByteBuffer bb) throws IOException{
        }
    }
}
chat.html
HTML
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<!DOCTYPE html>
<html>
    <head>
        <meta charset=UTF-8>
        <title>Tomcat WebSocket Chat</title>
        <script>
            var ws = new WebSocket("ws://localhost:8080/TomcatWebSocket/wschat/WsChatServlet");
            ws.onopen = function(){
            };
            ws.onmessage = function(message){
                document.getElementById("chatlog").textContent += message.data + "\n";
            };
            function postToServer(){
                ws.send(document.getElementById("msg").value);
                document.getElementById("msg").value = "";
            }
            function closeConnect(){
                ws.close();
            }
        </script>
    </head>
    <body>
        <textarea id="chatlog" readonly></textarea><br/>
        <input id="msg" type="text" />
        <button type="submit" id="sendButton" onClick="postToServer()">Send!</button>
        <button type="submit" id="sendButton" onClick="closeConnect()">End</button>
    </body>
</html>
web.xml
XML
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<?xml version="1.0" encoding="UTF-8"?>
 
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 
    <servlet>
        <servlet-name>WsChatServlet</servlet-name>
        <servlet-class>wsapp.WsChatServlet</servlet-class>
    </servlet>
 
    <servlet-mapping>
        <servlet-name>WsChatServlet</servlet-name>
        <url-pattern>/wschat/WsChatServlet</url-pattern>
    </servlet-mapping>
 
</web-app>
saswatanand commented

Thanks! The code snippet was useful to me.

thomasrossetto commented

thank you very much !

nirajsalot commented

Thanks for sharing this

rendeddula commented

i am getting some library files missing exceptions. can you send me war file for this project.

sulmansarwar commented

can you please provide the maven dependencies for this gist? Thanks.

sourav301 commented

Thanks Chitan. I was searching for an implementation of websocket and your example helped a lot. It worked perfect on different browsers on a computer. But i dont know way it did not work across different computers. i.e. messages from one computer is not being delivered to other computer.
Where is the problem?

robbyn commented

Hi there, I was wondering if the mmiList should be protected against concurrent usage.

IslamBesto commented

I'm using the tomcat version 7.0.39 and it does'nt work for me, it generate this exception :

GRAVE: "Servlet.service()" pour la servlet WsChatServlet a généré une exception
java.lang.ClassCastException: org.apache.coyote.Request cannot be cast to org.apache.coyote.http11.upgrade.UpgradeInbound

smerz commented

This code only works with Tomcat 7. Tomcat 8 the websocket classes appear to have been refactored.

joleye commented

@IslamBesto I'm using the tomcat version 7.0.34，And your mistakes as

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