java websocket学习

引言：

　　websocket，webservice傻傻分不清楚，都觉得是很高深的东西，理解中的webservice是一种协议，通信协议，类似http协议的那种，比如使用webservice协议调后台接口，而websocket呢？与socket挂钩？长连接？对未知的东西总是恐惧的，所以默默不敢说话

启航：

　　学习过程中突然接触到了websocket的简单讲解，哦，websocket也是一种协议，它类似ajax，但连接不中断，接到消息就响应。叫什么双端通信。websocket请求头是ws://或者wss://开头，非安全与安全，后面就和http请求类似。后台写法当然与默认的http servlet有些不同，但变化不大，与springMVC的requestMapping有些相似，接受到请求可以进行拦截等处理，当然也可以限制接收请求的具体参数。

概念来一波：

原先实现模拟双端通信的手段：　　

在WebSocket规范提出之前，开发人员若要实现这些实时性较强的功能，经常会使用折衷的解决方法：轮询（polling）和Comet技术。其实后者本质上也是一种轮询，只不过有所改进。

　　轮询是最原始的实现实时Web应用的解决方案。轮询技术要求客户端以设定的时间间隔周期性地向服务端发送请求，频繁地查询是否有新的数据改动。明显地，这种方法会导致过多不必要的请求，浪费流量和服务器资源。

　　Comet技术又可以分为长轮询和流技术。长轮询改进了上述的轮询技术，减小了无用的请求。它会为某些数据设定过期时间，当数据过期后才会向服务端发送请求；这种机制适合数据的改动不是特别频繁的情况。流技术通常是指客户端使用一个隐藏的窗口与服务端建立一个HTTP长连接，服务端会不断更新连接状态以保持HTTP长连接存活；这样的话，服务端就可以通过这条长连接主动将数据发送给客户端；流技术在大并发环境下，可能会考验到服务端的性能。

　　这两种技术都是基于请求-应答模式，都不算是真正意义上的实时技术；它们的每一次请求、应答，都浪费了一定流量在相同的头部信息上，并且开发复杂度也较大。

特点：

　　1、双端通信

　　2、建立在TCP之上

　　3、协议标识符是ws（如果加密，则为wss），服务器网址就是 URL。

接入：

　　注意：JavaEE 7中出了JSR-356:Java API for WebSocket规范。不少Web容器，如Tomcat,Nginx,Jetty等都支持WebSocket。Tomcat从7.0.27开始支持 WebSocket，从7.0.47开始支持JSR-356

websocket客户端：

　　在客户端，没有必要为 WebSockets 使用 JavaScript 库。实现 WebSockets 的 Web 浏览器将通过 WebSockets 对象公开所有必需的客户端功能（主要指支持 Html5 的浏览器）。

客户端API：　　

　　以下 API 用于创建 WebSocket 对象。

　　var Socket = new WebSocket(url, [protocol] );

　　以上代码中的第一个参数 url, 指定连接的 URL。第二个参数 protocol 是可选的，指定了可接受的子协议。

　　WebSocket 属性

　　以下是 WebSocket 对象的属性。假定我们使用了以上代码创建了 Socket 对象：

属性	描述
Socket.readyState	只读属性 readyState 表示连接状态，可以是以下值：0 - 表示连接尚未建立。1 - 表示连接已建立，可以进行通信。2 - 表示连接正在进行关闭。3 - 表示连接已经关闭或者连接不能打开。
Socket.bufferedAmount	只读属性 bufferedAmount 已被 send() 放入正在队列中等待传输，但是还没有发出的 UTF-8 文本字节数。

　　WebSocket 事件

　　以下是 WebSocket 对象的相关事件。假定我们使用了以上代码创建了 Socket 对象：

事件	事件处理程序	描述
open	Socket.onopen	连接建立时触发
message	Socket.onmessage	客户端接收服务端数据时触发
error	Socket.onerror	通信发生错误时触发
close	Socket.onclose	连接关闭时触发

　　WebSocket 方法

　　以下是 WebSocket 对象的相关方法。假定我们使用了以上代码创建了 Socket 对象：

方法	描述
Socket.send()	使用连接发送数据
Socket.close()	关闭连接

　　　　客户端实例：　　　

<%--
  Created by IntelliJ IDEA.
  User: zhen
  Date: 2018/12/10
  Time: 17:36
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>welcome page</title>
</head>
<body>
    welcome to ssm all annotation project!

    <input id="text" type="text"/>
    <button onclick="send()">发送消息</button>
    <hr/>
    <button onclick="closeWebSocket()">关闭webSocket连接</button>
    <hr/>
    <div id="message"></div>
    </body>

    <script type="text/javascript">
        var webSocket = null;
        //判断当前浏览器是否支持webSocket
        if ('WebSocket' in window) {
            webSocket = new WebSocket("ws://localhost:8080/spring4webSocket/myHandler")
        } else {
            alert("当前浏览器 Not support webSocket");
        }

        webSocket.onerror = onError;
        webSocket.onopen = onOpen;
        webSocket.onmessage = onMessage;
        webSocket.onclose = onClose;

        function onError() {
            setMessageInnerHTML("WebSocket连接发生错误");
        }

        function onOpen() {
            setMessageInnerHTML("WebSocket连接成功");
        }

        function onMessage(event){
            //将接受到的数据直接输出
            setMessageInnerHTML(event.data);
        }

        function onClose() {
            setMessageInnerHTML("webSocket连接关闭");
        }

        function setMessageInnerHTML(message) {
            var messageDiv = document.getElementById("message");
            messageDiv.innerHTML = messageDiv.innerHTML + "<br/>" + message;
        }

        //监听串口关闭事件，当窗口关闭时，主动去关闭webSocket连接，防止还没断开就关闭窗口，srever端会抛异常
        window.onbeforeunload = function (ev) {
            closeWebSocket();
        }

        function closeWebSocket(){
            webSocket.close();
        }


        //发送消息
        function send() {
            var message = document.getElementById("text").value;
            webSocket.send(message);
        }

    </script>
</html>

客户端实例

服务端（java）：

　　基于servlet api：

　　　　1、导入有关jar包　　　　　

        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>

　　API：

　　　　@ServerEnpoint 声明webSocket服务端，指明映射url

　　　　@OnMessage 标注接收到消息执行监听方法

　　　　@OnOpen 标注打开连接时候执行监听方法

　　　　@OnClose 标注关闭连接时执行监听方法

　　　　@OnError 标注连接异常时执行监听方法

　　服务端实例：

package com.zhen.websocket;

/**
 * @author zhen
 * @Date 2018/12/6 10:29
 */

import java.io.*;
import java.util.*;
import javax.websocket.EncodeException;
import javax.websocket.OnClose;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;

 // @ServerEndpoint 注解允许你声明一个WeoSocket，定义url映射，定义编码和解码
@ServerEndpoint(
    value="/story/notifications",
    encoders={StickerEncoder.class},
    decoders={StickerDecoder.class}
   )
public class StoryWebSocket {


    private static final List<Sticker> stickers = Collections.synchronizedList(new LinkedList<Sticker>());
    private static final Set<Session> sessions = Collections.synchronizedSet(new HashSet<Session>());

     @OnMessage
     public void onMessage(Session session, Sticker sticker){
         // 有消息从客户端发送过来，保存到列表中，然后通知所有的客户端
         stickers.add(sticker);
         for(Session openSession : sessions){
             try {
                 openSession.getBasicRemote().sendObject(sticker);
             } catch (IOException | EncodeException e) {
                 sessions.remove(openSession);
             }
         }
     }

     @OnOpen
     public void onOpen(Session session) throws IOException, EncodeException{
         // 有新的客户端连接时，保存此客户端的session，并且把当前所有的sticker发送给它
         sessions.add(session);
         for(Sticker sticker : stickers){
             session.getBasicRemote().sendObject(sticker);
         }
     }

     @OnClose
     public void onClose(Session session){
         // 有客户端断开连接时 ，从session列表中移除此客户端的session
         sessions.remove(session);
     }


}

服务端实例

看的有些混乱不能很好理解的时候就敲一些例子，功能出来就更容易理解了。

跟着下面两篇教程的案例

package com.zhen.websocket;

/**
 * @author zhen
 * @Date 2018/12/6 10:28
 */
public class Sticker {

    private int x;
    private int y;
    private String image;

    public Sticker() {
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }
}

package com.zhen.websocket;

import javax.json.JsonObject;
import javax.json.JsonReader;
import javax.json.spi.JsonProvider;
import javax.websocket.DecodeException;
import javax.websocket.Decoder;
import javax.websocket.EndpointConfig;
import java.io.IOException;
import java.io.Reader;


/**
 * @author zhen
 * @Date 2018/12/6 11:08
 * 用来读取webSocket流中的数据使用Decode.TextStream接口。 这个接口允许你读取数据从socket中通过JsonReader对象，构造传入Reader对象，并且转换客户端返回文本JSON数据
 */
public class StickerDecoder implements Decoder.TextStream<Sticker>{

    // Do not create a JsonReader object. To create readers and writes, use the
    // JsonProvider class.

    @Override
    public void init(EndpointConfig config) {
        // TODO Auto-generated method stub
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
    }

    @Override
    public Sticker decode(Reader reader) throws DecodeException, IOException {
        JsonProvider provider = JsonProvider.provider();
        JsonReader jsonReader = provider.createReader(reader);
        JsonObject jsonSticker = jsonReader.readObject();

        Sticker sticker = new Sticker();
        sticker.setX(jsonSticker.getInt("x"));
        sticker.setY(jsonSticker.getInt("y"));
        sticker.setImage(jsonSticker.getString("sticker"));
        return sticker;
    }

}

package com.zhen.websocket;

import javax.json.JsonObject;
import javax.json.JsonWriter;
import javax.json.spi.JsonProvider;
import javax.websocket.EncodeException;
import javax.websocket.Encoder;
import javax.websocket.EndpointConfig;
import java.io.IOException;
import java.io.Writer;

/**
 * @author zhen
 * @Date 2018/12/6 10:59
 * 这个类编码Sticker对象并且传递给WebSocket服务器通过写入流中
 */
public class StickerEncoder implements Encoder.TextStream<Sticker> {

    @Override
    public void init(EndpointConfig config) {
        // TODO Auto-generated method stub
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
    }

    @Override
    public void encode(Sticker sticker, Writer writer) throws EncodeException, IOException {
        JsonProvider provider = JsonProvider.provider();
        JsonObject jsonSticker = provider.createObjectBuilder()
            .add("action", "add")
            .add("x", sticker.getX())
            .add("y", sticker.getY())
            .add("sticker", sticker.getImage())
            .build();
        JsonWriter jsonWriter = provider.createWriter(writer);
        jsonWriter.write(jsonSticker);
    }

}

package com.zhen.websocket;

/**
 * @author zhen
 * @Date 2018/12/6 10:29
 */

import java.io.*;
import java.util.*;
import javax.websocket.EncodeException;
import javax.websocket.OnClose;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;

 // @ServerEndpoint 注解允许你声明一个WeoSocket，定义url映射，定义编码和解码
@ServerEndpoint(
    value="/story/notifications",
    encoders={StickerEncoder.class},
    decoders={StickerDecoder.class}
   )
public class StoryWebSocket {


    private static final List<Sticker> stickers = Collections.synchronizedList(new LinkedList<Sticker>());
    private static final Set<Session> sessions = Collections.synchronizedSet(new HashSet<Session>());

     @OnMessage
     public void onMessage(Session session, Sticker sticker){
         // 有消息从客户端发送过来，保存到列表中，然后通知所有的客户端
         stickers.add(sticker);
         for(Session openSession : sessions){
             try {
                 openSession.getBasicRemote().sendObject(sticker);
             } catch (IOException | EncodeException e) {
                 sessions.remove(openSession);
             }
         }
     }

     @OnOpen
     public void onOpen(Session session) throws IOException, EncodeException{
         // 有新的客户端连接时，保存此客户端的session，并且把当前所有的sticker发送给它
         sessions.add(session);
         for(Sticker sticker : stickers){
             session.getBasicRemote().sendObject(sticker);
         }
     }

     @OnClose
     public void onClose(Session session){
         // 有客户端断开连接时 ，从session列表中移除此客户端的session
         sessions.remove(session);
     }


}




var socket = null;
function initialize() {
    var canvas = document.getElementById("board");
    var ctx = canvas.getContext("2d");
    var img = document.getElementById("background_img");
    ctx.drawImage(img, 0, 0);
    socket = new WebSocket("ws://localhost:8080/stickStory/story/notifications");
    socket.onmessage = onSocketMessage;
}

function drag(ev) {
    var bounds = ev.target.getBoundingClientRect();
    var draggedSticker = {
        sticker: ev.target.getAttribute("data-sticker"),
        offsetX: ev.clientX - bounds.left,
        offsetY: ev.clientY - bounds.top
    };
    var draggedText = JSON.stringify(draggedSticker);
    ev.dataTransfer.setData("text", draggedText);
}

function drop(ev) {
    ev.preventDefault();
    var bounds = document.getElementById("board").getBoundingClientRect();
    var draggedText = ev.dataTransfer.getData("text");
    var draggedSticker = JSON.parse(draggedText);
    var stickerToSend = {
        action: "add",
        x: ev.clientX - draggedSticker.offsetX - bounds.left,
        y: ev.clientY - draggedSticker.offsetY - bounds.top,
        sticker: draggedSticker.sticker
    };
    socket.send(JSON.stringify(stickerToSend));
    log("Sending Object " + JSON.stringify(stickerToSend));
}

function allowDrop(ev) {
    ev.preventDefault();
}

function onSocketMessage(event) {
    if (event.data) {
        var receivedSticker = JSON.parse(event.data);
        log("Received Object: " + JSON.stringify(receivedSticker));
        if (receivedSticker.action === "add") {
            var imageObj = new Image();
            imageObj.onload = function() {
                var canvas = document.getElementById("board");
                var context = canvas.getContext("2d");
                context.drawImage(imageObj, receivedSticker.x, receivedSticker.y);
            };
            imageObj.src = "resources/stickers/" + receivedSticker.sticker;
        }
    }
}

function toggleLog() {
    var log = document.getElementById("logContainer");
    if (!log.getAttribute("style")) {
        log.setAttribute("style", "display:block;");
    } else {
        log.setAttribute("style", "");
    }
}

var logCount = 0;
function log(logstr) {
    var logElement = document.getElementById("log");
    logElement.innerHTML = "<b>[" + logCount + "]: </b>" + logstr + "<br>" + logElement.innerHTML;
    logCount++;
}

window.onload = initialize;


<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html>
<html>
<head>
    <title>Sticker Story</title>
    <link href="resources/styles.css" rel="stylesheet" type="text/css" >
    <script src="resources/story-page.js" type="text/javascript"></script>
</head>
<body>
<header>
    <h1>Sticker Story Book</h1>
</header>
<nav>
    Drag stickers from the left bar to the canvas.
</nav>
<aside>
    <h2>Stickers</h2>
    <div id="stickerContainer">
        <img src="resources/stickers/bear.png"
             data-sticker="bear.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
        <img src="resources/stickers/chicken.png"
             data-sticker="chicken.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
        <img src="resources/stickers/leopard.png"
             data-sticker="leopard.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
        <img src="resources/stickers/monkey.png"
             data-sticker="monkey.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
        <img src="resources/stickers/horse.png"
             data-sticker="horse.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
        <img src="resources/stickers/tiger.png"
             data-sticker="tiger.png"
             style="float:left"
             draggable="true" ondragstart="drag(event);" >
    </div>
</aside>
<div id="content">
    <canvas id="board" width="1000" height="580" ondrop="drop(event);"
            ondragover="allowDrop(event);">
        Canvas Not Supported.
    </canvas>
    <img src="resources/canvas2.png" id="background_img"
         width="1000" height="580" style="display:none;"/>
</div>
<footer>
    <small>Made with HTML5 + WebSockets and JSON</small>
    <ol>
        <li onclick="toggleLog();">Log</li>
    </ol>
</footer>
<div id="logContainer">
    <h2>log</h2>
    <div id="log"></div>
</div>
</body>
</html>


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zhen</groupId>
    <artifactId>StickStory</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>


    <dependencies>

        <!-- Servlet -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
        </dependency>


        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- JSON工具包 -->
        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.json</artifactId>
            <version>1.0.4</version>
        </dependency>




    </dependencies>

    <build>
        <plugins>
            <!-- 编译插件 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>

            <!-- tomcat 插件 -->
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <port>8080</port>
                    <path>/stickStory</path>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

第一篇敲的项目代码

这里接受返回消息用到了转换器，接受对象类型json返回对象类型json

实现发布订阅模式

项目目录如下：

第二篇敲的项目代码：

package com.zhen.model;

/**
 * @author zhen
 * @Date 2018/12/6 15:30
 */
public class Device {

    private int id;
    private String name;
    private String status;
    private String type;
    private String description;

    public Device() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}


package com.zhen.websocket;

import com.zhen.model.Device;

import javax.enterprise.context.ApplicationScoped;
import javax.json.JsonObject;
import javax.json.spi.JsonProvider;
import javax.websocket.Session;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * @author zhen
 * @Date 2018/12/6 15:50
 */
@ApplicationScoped
public class DeviceSessionHandler {

    private final Set<Session> sessions = new HashSet<>();
    private final Set<Device> devices = new HashSet<>();
    private static AtomicInteger deviceId = new AtomicInteger(0);

    public void addSession(Session session) {
        sessions.add(session);
        for (Device device : devices) {
            JsonObject addMessage = createAndMessage(device);
            sendToSession(session, addMessage);
        }
    }

    public void removeSession(Session session) {
        sessions.remove(session);
    }

    public void addDevice(Device device) {
        device.setId(deviceId.incrementAndGet());
        devices.add(device);
        JsonObject addMessage = createAndMessage(device);
        sendToAllConnectedSessions(addMessage);
    }

    public void removeDevice(int id) {
        Device device = getDeviceById(id);
        if (device != null) {
            devices.remove(device);
            JsonProvider provider = JsonProvider.provider();
            JsonObject removeMessage = provider.createObjectBuilder()
                .add("action", "remove")
                .add("id", id)
                .build();
            sendToAllConnectedSessions(removeMessage);
        }
    }

    public void toggleDevice(int id) {
        JsonProvider provider = JsonProvider.provider();
        Device device = getDeviceById(id);
        if (device != null) {
            if ("On".equals(device.getStatus())) {
                device.setStatus("Off");
            } else {
                device.setStatus("On");
            }
            JsonObject updateDevMessage = provider.createObjectBuilder()
                .add("action", "toggle")
                .add("id", device.getId())
                .add("status", device.getStatus())
                .build();
                sendToAllConnectedSessions(updateDevMessage);
        }
    }

    public List<Device> getDevices(){
        return new ArrayList<>(devices);
    }

    public Device getDeviceById(int id) {
        for (Device device : devices) {
            if (device.getId() == id) {
                return device;
            }
        }
        return null;
    }

    public JsonObject createAndMessage(Device device) {
        JsonProvider provider = JsonProvider.provider();
        JsonObject addMessage = provider.createObjectBuilder()
            .add("action", "add")
            .add("name", device.getName())
            .add("type", device.getType())
            .add("status", device.getStatus())
            .add("description", device.getDescription())
            .build();
        return addMessage;
    }

    private void sendToAllConnectedSessions(JsonObject message) {
        for (Session session : sessions) {
            sendToSession(session, message);
        }
    }

    private void sendToSession(Session session, JsonObject message) {
        try{
            session.getBasicRemote().sendText(message.toString());
        } catch (IOException ex) {
            sessions.remove(session);
            Logger.getLogger(DeviceSessionHandler.class.getName()).log(Level.SEVERE, null, ex);
        }
    }


}

package com.zhen.websocket;

import com.zhen.model.Device;

import javax.enterprise.context.ApplicationScoped;
import javax.inject.Inject;
import javax.json.Json;
import javax.json.JsonObject;
import javax.json.JsonReader;
import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.StringReader;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * @author zhen
 * @Date 2018/12/6 15:32
 */
@ApplicationScoped
@ServerEndpoint("/actions")
public class DeviceWebSocketServer {

    @Inject
    private DeviceSessionHandler sessionHandler = new DeviceSessionHandler();

    @OnOpen
    public void open(Session session) {
        sessionHandler.addSession(session);
    }

    @OnClose
    public void close(Session session) {
        sessionHandler.removeSession(session);
    }

    @OnError
    public void onError(Throwable error) {
        Logger.getLogger(DeviceWebSocketServer.class.getName()).log(Level.SEVERE, null, error);
    }

    @OnMessage
    public void handleMessage(Session session, String message) {
        try(JsonReader reader = Json.createReader(new StringReader(message))){
            JsonObject jsonMessage = reader.readObject();

            if ("add".equals(jsonMessage.getString("action"))) {
                Device device = new Device();
                device.setName(jsonMessage.getString("name"));
                device.setDescription(jsonMessage.getString("description"));
                device.setType(jsonMessage.getString("type"));
                device.setStatus("Off");
                sessionHandler.addDevice(device);
            }

            if ("remove".equals(jsonMessage.getString("action"))) {
                int id = (int) jsonMessage.getInt("id");
                sessionHandler.removeDevice(id);
            }

            if ("toggle".equals(jsonMessage.getString("action"))) {
                int id = (int) jsonMessage.getInt("id");
                sessionHandler.toggleDevice(id);
            }
        }
    }
}


<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html>
<html>
<head>
    <title>Index</title>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
    <link rel="stylesheet" href="style.css">
    <script src="websocket.js"></script>
</head>
<body>
<div id="wrapper">
    <h1>Java WebSocket Home</h1>
    <p>Welcome to the Java WebSocket Home. Click the Add a device button to start adding devices.</p>
    <br/>
    <div id="addDevice">
        <div class="button"><a href="#" onclick="showForm()">Add a device</a> </div>
        <form id="addDeviceForm">
            <h3>Add a new device</h3>
            <span>Name: <input type="text" name="device_name" id="device_name"></span>
            <span>
                Type:
                <select id="device_type">
                    <option name="type" value="Appliance">Appliance</option>
                    <option name="type" value="Electronics">Electronics</option>
                    <option name="type" value="Lights">Lights</option>
                    <option name="type" value="Other">Other</option>
                </select>
            </span>

            <span>
                Description:<br/>
                <textarea name="description" id="device_description" rows="2" cols="50"></textarea>
            </span>

            <input type="button" class="button" value="Add" onclick="formSubmit();">
            <input type="reset" class="button" value="Cancel" onclick="hideForm();">
        </form>
    </div>
    <br/>
    <h3>Currently connected devices:</h3>
    <div id="content"></div>
</div>
</body>
</html>


body {
    font-family: Arial, Helvetica, sans-serif;
    font-size: 80%;
    background-color: #1f1f1f;
}

#wrapper {
     960px;
    margin: auto;
    text-align: left;
    color: #d9d9d9;
}

p {
    text-align: left;
}

.button {
    display: inline;
    color: #fff;
    background-color: #f2791d;
    padding: 8px;
    margin: auto;
    border-radius: 8px;
    -moz-border-radius: 8px;
    -webkit-border-radius: 8px;
    box-shadow: none;
    border: none;
}

.button:hover {
    background-color: #ffb15e;
}
.button a, a:visited, a:hover, a:active {
    color: #fff;
    text-decoration: none;
}

#addDevice {
    text-align: center;
     960px;
    margin: auto;
    margin-bottom: 10px;
}

#addDeviceForm {
    text-align: left;
     400px;
    margin: auto;
    padding: 10px;
}

#addDeviceForm span {
    display: block;
}

#content {
    margin: auto;
     960px;
}

.device {
     180px;
    height: 110px;
    margin: 10px;
    padding: 16px;
    color: #fff;
    vertical-align: top;
    border-radius: 8px;
    -moz-border-radius: 8px;
    -webkit-border-radius: 8px;
    display: inline-block;
}

.device.off {
    background-color: #c8cccf;
}

.device span {
    display: block;
}

.deviceName {
    text-align: center;
    font-weight: bold;
    margin-bottom: 12px;
}

.removeDevice {
    margin-top: 12px;
    text-align: center;
}

.device.Appliance {
    background-color: #5eb85e;
}

.device.Appliance a:hover {
    color: #a1ed82;
}

.device.Electronics {
    background-color: #0f90d1;
}

.device.Electronics a:hover {
    color: #4badd1;
}

.device.Lights {
    background-color: #c2a00c;
}

.device.Lights a:hover {
    color: #fad232;
}

.device.Other {
    background-color: #db524d;
}

.device.Other a:hover {
    color: #ff907d;
}

.device a {
    text-decoration: none;
}

.device a:visited, a:active, a:hover {
    color: #fff;
}

.device a:hover {
    text-decoration: underline;
}


window.onload = init;
var socket = new WebSocket("ws://localhost:8080/webSocketHome/actions");
socket.onmessage = onMessage;

function onMessage(event) {
    var device = JSON.parse(event.data);
    if (device.action === "add") {
        printDeviceElement(device);
    }
    if (device.action === "remove") {
        document.getElementById(device.id).remove();
        //device.parentNode.removeChild(device);
    }
    if (device.action === "toggle") {
        var node = document.getElementById(device.id);
        var statusText = node.children[2];
        if (device.status === "On") {
            statusText.innerHTML = "Status: " + device.status + " (<a href="#" OnClick=toggleDevice(" + device.id + ")>Turn off</a>)";
        } else if (device.status === "Off") {
            statusText.innerHTML = "Status: " + device.status + " (<a href="#" OnClick=toggleDevice(" + device.id + ")>Turn on</a>)";
        }
    }
}

function addDevice(name, type, description) {
    var DeviceAction = {
        action: "add",
        name: name,
        type: type,
        description: description
    };
    socket.send(JSON.stringify(DeviceAction));
}

function removeDevice(element) {
    var id = element;
    var DeviceAction = {
        action: "remove",
        id: id
    };
    socket.send(JSON.stringify(DeviceAction));
}

function toggleDevice(element) {
    var id = element;
    var DeviceAction = {
        action: "toggle",
        id: id
    };
    socket.send(JSON.stringify(DeviceAction));
}

function printDeviceElement(device) {
    var content = document.getElementById("content");

    var deviceDiv = document.createElement("div");
    deviceDiv.setAttribute("id", device.id);
    deviceDiv.setAttribute("class", "device " + device.type);
    content.appendChild(deviceDiv);

    var deviceName = document.createElement("span");
    deviceName.setAttribute("class", "deviceName");
    deviceName.innerHTML = device.name;
    deviceDiv.appendChild(deviceName);

    var deviceType = document.createElement("span");
    deviceType.innerHTML = "<b>Type:</b> " + device.type;
    deviceDiv.appendChild(deviceType);

    var deviceStatus = document.createElement("span");
    if (device.status === "On") {
        deviceStatus.innerHTML = "<b>Status:</b> " + device.status + " (<a href="#" OnClick=toggleDevice(" + device.id + ")>Turn off</a>)";
    } else if (device.status === "Off") {
        deviceStatus.innerHTML = "<b>Status:</b> " + device.status + " (<a href="#" OnClick=toggleDevice(" + device.id + ")>Turn on</a>)";
        //deviceDiv.setAttribute("class", "device off");
    }
    deviceDiv.appendChild(deviceStatus);

    var deviceDescription = document.createElement("span");
    deviceDescription.innerHTML = "<b>Comments:</b> " + device.description;
    deviceDiv.appendChild(deviceDescription);

    var removeDevice = document.createElement("span");
    removeDevice.setAttribute("class", "removeDevice");
    removeDevice.innerHTML = "<a href="#" OnClick=removeDevice(" + device.id + ")>Remove device</a>";
    deviceDiv.appendChild(removeDevice);
}

function showForm() {
    document.getElementById("addDeviceForm").style.display = '';
}

function hideForm() {
    document.getElementById("addDeviceForm").style.display = "none";
}

function formSubmit() {
    var form = document.getElementById("addDeviceForm");
    var name = form.elements["device_name"].value;
    var type = form.elements["device_type"].value;
    var description = form.elements["device_description"].value;
    hideForm();
    document.getElementById("addDeviceForm").reset();
    addDevice(name, type, description);
}

function init() {
    hideForm();
}

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.zhen</groupId>
    <artifactId>WebSocketHome</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>


    <dependencies>

        <!-- Servlet -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.0.1</version>
        </dependency>


        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- JSON工具包 -->
        <dependency>
            <groupId>org.glassfish</groupId>
            <artifactId>javax.json</artifactId>
            <version>1.0.4</version>
        </dependency>




    </dependencies>

    <build>
        <plugins>
            <!-- 编译插件 -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                    <encoding>UTF-8</encoding>
                </configuration>
            </plugin>

            <!-- tomcat 插件 -->
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <port>8080</port>
                    <path>/webSocketHome</path>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

第二篇敲的代码

此案例利用websocket实现了一套增删改查

项目中使用了CDI注解，如@ApplicationScope，@Inject进行注入功能

项目结构：

spring的websocket支持：

　　spring4提供了对websocket的支持

<!-- spring-webSocket，不使用javaee7的api里面了，使用spring的封装 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-websocket</artifactId>
            <version>${spring.version}</version>
        </dependency>

服务端配置：

package com.zhen.spring_websocket.config;

import com.zhen.spring_websocket.service.MyHandler;
import com.zhen.spring_websocket.service.MyHandler1;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;

/**
 * @author zhen
 * @Date 2018/12/10 18:34
 */
@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(myHandler(),"/myHandler");
        registry.addHandler(myHandler1(),"/myHandler1").withSockJS();
    }

    public WebSocketHandler myHandler() {
        return new MyHandler();
    }

    public WebSocketHandler myHandler1() {
        return new MyHandler1();
    }
}

package com.zhen.spring_websocket.service;

import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.TextMessage;
import org.springframework.web.socket.WebSocketSession;
import org.springframework.web.socket.handler.AbstractWebSocketHandler;
import org.springframework.web.socket.handler.TextWebSocketHandler;

import java.io.IOException;

/**
 * @author zhen
 * @Date 2018/12/10 18:32
 * 此类实现WebSocketHandler，执行处理请求等操作，这里只是接受请求然后再将请求转发回去的功能
 */
public class MyHandler1 extends AbstractWebSocketHandler {
    @Override
    protected void handleTextMessage(WebSocketSession session, TextMessage message) {
        try{
            session.sendMessage(message);
        }catch (IOException e){
            e.printStackTrace();
        }

    }

    @Override
    public void afterConnectionEstablished(WebSocketSession session) throws Exception {
        super.afterConnectionEstablished(session);
    }

    @Override
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
        super.afterConnectionClosed(session, status);
    }
}

Handler并不一定是继承abstractWebSocketHandler，只要是WebSocketHandler的子类即可。

和servlet的websocket api差不多吧

这句代码：

registry.addHandler(myHandler1(),"/myHandler1").withSockJS();

是表示接受的是前端sockJs对象发送的请求。是spring-websocket模块的一个封装功能。

sockJs是什么呢？

在不支持WebSocket的情况下，也可以很简单地实现WebSocket的功能的，方法就是使用 SockJS。

它会优先选择WebSocket进行连接，但是当服务器或客户端不支持WebSocket时，会自动在 XHR流、XDR流、iFrame事件源、iFrame HTML文件、XHR轮询、XDR轮询、iFrame XHR轮询、JSONP轮询这几个方案中择优进行连接。

它是websocket客户端的拓展与补充。

使用sockJs之后，spring注册websocket链接就上面代码这样既可。

客户端：

　　引入sockjs.min.js

　　使用sockJs对象替代WebSocket对象发送请求，它的语法和原生几乎一致

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page session="false" %>
<html>
<head>
    <title>WebSocket with SockJS</title>
</head>
<body>
<h1>Welcome!</h1>
<ul id="ul">
</ul>
<script src="${pageContext.request.contextPath}/static/js/sockjs.min.js"></script>
<script>
    // SockJS与原生的WebSocket的方法基本是一致的，
    // 所以只需要将 new WebSocket(url); 换成 new SockJS(url); 就可以了
    var url = "/spring4webSocket/myHandler1";
    var sock = new SockJS(url);
    sock.onopen = function (ev) {
        console.log("opening");
        sayHey();
    };
    sock.onmessage = function (ev) {
        console.log(ev.data);
        var li = document.createElement("li");
        li.innerText = ev.data;
        document.getElementById("ul").appendChild(li);
        setTimeout(sayHey, 2000);
    };
    sock.onclose = function (ev) {
        console.log("closed");
    };
    function sayHey() {
        console.log("sending 'Hey guy!'");
        sock.send("Hey guy!");
    };
</script>
</body>
</html>

spring的封装还有基于stomp的部分：

　　这个没理解好，以后再做研究。与spring配置请求的也涉及到再做补充。虽然写过demo，但是不太理解，用的springbot，使用了spring security的例子，暂过。

参考链接：https://www.jianshu.com/p/942a2b16e26c

参考链接：https://baike.baidu.com/item/WebSocket/1953845?fr=aladdin

参考链接：https://www.cnblogs.com/jingmoxukong/p/7755643.html

参考链接：http://www.ruanyifeng.com/blog/2017/05/websocket.html

参考链接：http://www.cnblogs.com/xdp-gacl/p/5193279.html

参考链接：https://blog.csdn.net/john_62/article/details/78208177

参考链接：https://blog.csdn.net/dadiyang/article/details/83715569

此学习得出的经验之谈：如果暂时理解不了，就先使用他，然后再理解　　

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原文地址：https://www.cnblogs.com/aigeileshei/p/10101802.html