java websocket的开发案例与注意事项

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第一步：源码

* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.websocket.chat;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.atomic.AtomicInteger;

import javax.servlet.http.HttpServletRequest;

import org.apache.catalina.websocket.MessageInbound;
import org.apache.catalina.websocket.StreamInbound;
import org.apache.catalina.websocket.WebSocketServlet;
import org.apache.catalina.websocket.WsOutbound;

/**
* Example web socket servlet for chat.
*/
public class ChatWebSocketServlet extends WebSocketServlet {

    private static final long serialVersionUID = 1L;

    private static final String GUEST_PREFIX = "Guest";

    private final AtomicInteger connectionIds = new AtomicInteger(0);
    private final Set<ChatMessageInbound> connections =
            new CopyOnWriteArraySet<ChatMessageInbound>();

    @Override
    protected StreamInbound createWebSocketInbound(String subProtocol,
            HttpServletRequest request) {
        return new ChatMessageInbound(connectionIds.incrementAndGet());
    }

    private final class ChatMessageInbound extends MessageInbound {

        private final String nickname;

        private ChatMessageInbound(int id) {
            this.nickname = GUEST_PREFIX + id;
        }

        @Override
        protected void onOpen(WsOutbound outbound) {
            connections.add(this);
            String message = String.format("* %s %s",
                    nickname, "has joined.");
            broadcast(message);
        }

        @Override
        protected void onClose(int status) {
            connections.remove(this);
            String message = String.format("* %s %s",
                    nickname, "has disconnected.");
            broadcast(message);
        }

        @Override
        protected void onBinaryMessage(ByteBuffer message) throws IOException {
            throw new UnsupportedOperationException(
                    "Binary message not supported.");
        }

        @Override
        protected void onTextMessage(CharBuffer message) throws IOException {
            // Never trust the client
            String filteredMessage = String.format("%s: %s",
                    nickname, "");
            broadcast(filteredMessage);
        }

        private void broadcast(String message) {
            for (ChatMessageInbound connection : connections) {
                try {
                    CharBuffer buffer = CharBuffer.wrap(message);
                    connection.getWsOutbound().writeTextMessage(buffer);
                } catch (IOException ignore) {
                    // Ignore
                }
            }
        }
    }

}

第二步 websocket部署

<servlet>
        <servlet-name>wsChat</servlet-name>
        <servlet-class>com.websocket.chat.ChatWebSocketServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>wsChat</servlet-name>
        <url-pattern>/websocket/chat</url-pattern>
    </servlet-mapping>

第三步 html5

<!DOCTYPE html>
<html>
<head>
    <title>Apache Tomcat WebSocket Examples: Chat</title>
    <style type="text/css">
        input#chat {
            width: 410px
        }

        #console-container {
            width: 400px;
        }

        #console {
            border: 1px solid #CCCCCC;
            border-right-color: #999999;
            border-bottom-color: #999999;
            height: 170px;
            overflow-y: scroll;
            padding: 5px;
            width: 100%;
        }

        #console p {
            padding: 0;
            margin: 0;
        }
    </style>
    <script type="text/javascript">
        var Chat = {};

        Chat.socket = null;

        Chat.connect = (function(host) {
            if ('WebSocket' in window) {
                Chat.socket = new WebSocket(host);
            } else if ('MozWebSocket' in window) {
                Chat.socket = new MozWebSocket(host);
            } else {
                Console.log('Error: WebSocket is not supported by this browser.');
                return;
            }

            Chat.socket.onopen = function () {
                Console.log('Info: WebSocket connection opened.');
                document.getElementById('chat').onkeydown = function(event) {
                    if (event.keyCode == 13) {
                        Chat.sendMessage();
                    }
                };
            };

            Chat.socket.onclose = function () {
                document.getElementById('chat').onkeydown = null;
                Console.log('Info: WebSocket closed.');
            };

            Chat.socket.onmessage = function (message) {
                Console.log(message.data);
            };
        });

        Chat.initialize = function() {
            if (window.location.protocol == 'http:') {
                Chat.connect('ws://' + window.location.host +'/btc/websocket/chat');
            } else {
                Chat.connect('wss://' + window.location.host + '/btc/websocket/chat');
            }
        };

        Chat.sendMessage = (function() {
            var message = document.getElementById('chat').value;
            if (message != '') {
                Chat.socket.send(message);
                document.getElementById('chat').value = '';
            }
        });

        var Console = {};

        Console.log = (function(message) {
            var console = document.getElementById('console');
            var p = document.createElement('p');
            p.style.wordWrap = 'break-word';
            p.innerHTML = message;
            console.appendChild(p);
            while (console.childNodes.length > 25) {
                console.removeChild(console.firstChild);
            }
            console.scrollTop = console.scrollHeight;
        });

        Chat.initialize();

    </script>
</head>
<body>
<noscript><h2 style="color: #ff0000">Seems your browser doesn't support Javascript! Websockets rely on Javascript being enabled. Please enable
    Javascript and reload this page!</h2></noscript>
<div>
    <p>
        <input type="text" placeholder="type and press enter to chat" id="chat">
    </p>
    <div id="console-container">
        <div id="console"></div>
    </div>
</div>
</body>
</html>

第四步需要引入相关jar : tomcat-coyote.jar,catalina.jar .

最后编译，然后运行。访问chat.html。注意红色的标记。

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