Spring boot と WebSockets でアプリを作成してみた【Real-Time Chat App】

## WebSocketとは?
WebSocketとは、WebサーバとWebブラウザの間で双方向通信できるようにする技術仕様。サーバ側から任意のタイミングで送信を開始でき、プッシュ型の情報配信アプリケーションを手軽に実装できる。

## 1.プロジェクトを作成する
公式：spring initializr

① ブラウザを開き、(https://start.spring.io/) を入力し、開く
② 下記を入力し、Dependenciesで下記を選択し、『GENERATE』ボタンを押す

Project: Maven
Language: Java
SpringBoot: 3.0.8

Group: com.alibou
Artifact: chat
Name : chat
Description: Demo project for Spring Boot chat application
Package name: com.alibou.chat

##### Dependencies
Spring Web
WebSocket
Lombok

## 2.バックエンドを実装する

① src/main/java/com/alibou/chatに configファイルとWebSocketConfig.javaを作成する。

``` config/WebSocketConfig.java
package com.alibou.chat.config;

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.messaging.SessionDisconnectEvent;

@Component
@RequiredArgsConstructor
@Slf4j
public class WebSocketEventLister {
    @EventListener
    public void handleWebSocketDisconnectListener(
        SessionDisconnectEvent event
    ){
        // TODO -- to be implemented
    }
}
```
② src/main/java/com/alibou/chatに chatファイルとChatController.javaを作成する。

```chat/ChatController.java
package com.alibou.chat.chat;

import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.Payload;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
import org.springframework.stereotype.Controller;

@Controller
public class ChatController {

    @MessageMapping("/chat.sendMessage")
    @SendTo("/topic/public")
    public ChatMessage sendMessage(
      @Payload ChatMessage chatMessage
    ) {
      return chatMessage;
    }

    @MessageMapping("/chat.addUser")
    @SendTo("/topic/public")
    public ChatMessage addUser(
      @Payload ChatMessage chatMessage,
      SimpMessageHeaderAccessor headerAccessor
    ) {
        //Add username in web socket session
        headerAccessor.getSessionAttributes().put("username",chatMessage.getSender());
        return chatMessage;
    }
}
```
③ chatファイルにChatMessage.javaを作成する。

```chat/ChatMessage.java
package com.alibou.websocket.chat;

import lombok.*;

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class ChatMessage {

    private MessageType type;
    private String content;
    private String sender;

}
```
④ chatファイルにMessageType.javaを作成する。

```chat/MessageType.java
package com.alibou.websocket.chat;

public enum MessageType {

    CHAT,
    JOIN,
    LEAVE
}
```
⑤ src/main/java/com/alibou/chatに configファイルとWebSocket EventListener.javaを作成する。

```chat/WebSocketEventListener.java
package com.alibou.websocket.config;

import com.alibou.websocket.chat.ChatMessage;
import com.alibou.websocket.chat.MessageType;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.context.event.EventListener;
import org.springframework.messaging.simp.SimpMessageSendingOperations;
import org.springframework.messaging.simp.stomp.StompHeaderAccessor;
import org.springframework.stereotype.Component;
import org.springframework.web.socket.messaging.SessionDisconnectEvent;

@Component
@Slf4j
@RequiredArgsConstructor
public class WebSocketEventListener {

    private final SimpMessageSendingOperations messagingTemplate;

    @EventListener
    public void handleWebSocketDisconnectListener(SessionDisconnectEvent event) {
        StompHeaderAccessor headerAccessor = StompHeaderAccessor.wrap(event.getMessage());
        String username = (String) headerAccessor.getSessionAttributes().get("username");
        if (username != null) {
            log.info("user disconnected: {}", username);
            var chatMessage = ChatMessage.builder()
                    .type(MessageType.LEAVE)
                    .sender(username)
                    .build();
            messagingTemplate.convertAndSend("/topic/public", chatMessage);
        }
    }

}
```
## 3.フロントエンドを実装する

① src/main/resource/staticにindex.htmlを作成する

```static/index.html
<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0">
    <title>Spring Boot WebSocket Chat Application</title>
    <link rel="stylesheet" href="/css/main.css" />
</head>
<body>
<noscript>
    <h2>Sorry! Your browser doesn't support Javascript</h2>
</noscript>

<div id="username-page">
    <div class="username-page-container">
        <h1 class="title">Type your username to enter the Chatroom</h1>
        <form id="usernameForm" name="usernameForm">
            <div class="form-group">
                <input type="text" id="name" placeholder="Username" autocomplete="off" class="form-control" />
            </div>
            <div class="form-group">
                <button type="submit" class="accent username-submit">Start Chatting</button>
            </div>
        </form>
    </div>
</div>

<div id="chat-page" class="hidden">
    <div class="chat-container">
        <div class="chat-header">
            <h2>Spring WebSocket Chat Demo - By Alibou</h2>
        </div>
        <div class="connecting">
            Connecting...
        </div>
        <ul id="messageArea">

        </ul>
        <form id="messageForm" name="messageForm">
            <div class="form-group">
                <div class="input-group clearfix">
                    <input type="text" id="message" placeholder="Type a message..." autocomplete="off" class="form-control"/>
                    <button type="submit" class="primary">Send</button>
                </div>
            </div>
        </form>
    </div>
</div>

<script src="https://cdnjs.cloudflare.com/ajax/libs/sockjs-client/1.1.4/sockjs.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/stomp.js/2.3.3/stomp.min.js"></script>
<script src="/js/main.js"></script>
</body>
</html>
```
② src/main/resource/staticにcssファイルとmain.cssを作成する

```main.css
* {
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}

html,body {
    height: 100%;
    overflow: hidden;
}

body {
    margin: 0;
    padding: 0;
    font-weight: 400;
    font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
    font-size: 1rem;
    line-height: 1.58;
    color: #333;
    background-color: #f4f4f4;
    height: 100%;
}

.clearfix:after {
    display: block;
    content: "";
    clear: both;
}

.hidden {
    display: none;
}

.form-control {
    width: 100%;
    min-height: 38px;
    font-size: 15px;
    border: 1px solid #c8c8c8;
}

.form-group {
    margin-bottom: 15px;
}

input {
    padding-left: 10px;
    outline: none;
}

h1, h2, h3, h4, h5, h6 {
    margin-top: 20px;
    margin-bottom: 20px;
}

h1 {
    font-size: 1.7em;
}

a {
    color: #6db33f;
}

button {
    box-shadow: none;
    border: 1px solid transparent;
    font-size: 14px;
    outline: none;
    line-height: 100%;
    white-space: nowrap;
    vertical-align: middle;
    padding: 0.6rem 1rem;
    border-radius: 2px;
    transition: all 0.2s ease-in-out;
    cursor: pointer;
    min-height: 38px;
}

button.default {
    background-color: #e8e8e8;
    color: #333;
    box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.12);
}

button.primary {
    background-color: #6db33f;
    box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.12);
    color: #fff;
}

button.accent {
    background-color: #6db33f;
    box-shadow: 0 2px 2px 0 rgba(0, 0, 0, 0.12);
    color: #fff;
}

#username-page {
    text-align: center;
}

.username-page-container {
    background: #fff;
    box-shadow: 0 1px 11px rgba(0, 0, 0, 0.27);
    border-radius: 2px;
    width: 100%;
    max-width: 500px;
    display: inline-block;
    margin-top: 42px;
    vertical-align: middle;
    position: relative;
    padding: 35px 55px 35px;
    min-height: 250px;
    position: absolute;
    top: 50%;
    left: 0;
    right: 0;
    margin: 0 auto;
    margin-top: -160px;
}

.username-page-container .username-submit {
    margin-top: 10px;
}


#chat-page {
    position: relative;
    height: 100%;
}

.chat-container {
    max-width: 700px;
    margin-left: auto;
    margin-right: auto;
    background-color: #fff;
    box-shadow: 0 1px 11px rgba(0, 0, 0, 0.27);
    margin-top: 30px;
    height: calc(100% - 60px);
    max-height: 600px;
    position: relative;
}

#chat-page ul {
    list-style-type: none;
    background-color: #FFF;
    margin: 0;
    overflow: auto;
    overflow-y: scroll;
    padding: 0 20px 0px 20px;
    height: calc(100% - 150px);
}

#chat-page #messageForm {
    padding: 20px;
}

#chat-page ul li {
    line-height: 1.5rem;
    padding: 10px 20px;
    margin: 0;
    border-bottom: 1px solid #f4f4f4;
}

#chat-page ul li p {
    margin: 0;
}

#chat-page .event-message {
    width: 100%;
    text-align: center;
    clear: both;
}

#chat-page .event-message p {
    color: #777;
    font-size: 14px;
    word-wrap: break-word;
}

#chat-page .chat-message {
    padding-left: 68px;
    position: relative;
}

#chat-page .chat-message i {
    position: absolute;
    width: 42px;
    height: 42px;
    overflow: hidden;
    left: 10px;
    display: inline-block;
    vertical-align: middle;
    font-size: 18px;
    line-height: 42px;
    color: #fff;
    text-align: center;
    border-radius: 50%;
    font-style: normal;
    text-transform: uppercase;
}

#chat-page .chat-message span {
    color: #333;
    font-weight: 600;
}

#chat-page .chat-message p {
    color: #43464b;
}

#messageForm .input-group input {
    float: left;
    width: calc(100% - 85px);
}

#messageForm .input-group button {
    float: left;
    width: 80px;
    height: 38px;
    margin-left: 5px;
}

.chat-header {
    text-align: center;
    padding: 15px;
    border-bottom: 1px solid #ececec;
}

.chat-header h2 {
    margin: 0;
    font-weight: 500;
}

.connecting {
    padding-top: 5px;
    text-align: center;
    color: #777;
    position: absolute;
    top: 65px;
    width: 100%;
}


@media screen and (max-width: 730px) {

    .chat-container {
        margin-left: 10px;
        margin-right: 10px;
        margin-top: 10px;
    }
}

@media screen and (max-width: 480px) {
    .chat-container {
        height: calc(100% - 30px);
    }

    .username-page-container {
        width: auto;
        margin-left: 15px;
        margin-right: 15px;
        padding: 25px;
    }

    #chat-page ul {
        height: calc(100% - 120px);
    }

    #messageForm .input-group button {
        width: 65px;
    }

    #messageForm .input-group input {
        width: calc(100% - 70px);
    }

    .chat-header {
        padding: 10px;
    }

    .connecting {
        top: 60px;
    }

    .chat-header h2 {
        font-size: 1.1em;
    }
}
```

③ src/main/resource/static/jsファイルのmain.jsを編集する

```static/js/main.js
'use strict';

var usernamePage = document.querySelector('#username-page');
var chatPage = document.querySelector('#chat-page');
var usernameForm = document.querySelector('#usernameForm');
var messageForm = document.querySelector('#messageForm');
var messageInput = document.querySelector('#message');
var messageArea = document.querySelector('#messageArea');
var connectingElement = document.querySelector('.connecting');

var stompClient = null;
var username = null;

var colors = [
    '#2196F3', '#32c787', '#00BCD4', '#ff5652',
    '#ffc107', '#ff85af', '#FF9800', '#39bbb0'
];

function connect(event) {
    username = document.querySelector('#name').value.trim();

    if(username) {
        usernamePage.classList.add('hidden');
        chatPage.classList.remove('hidden');

        var socket = new SockJS('/ws');
        stompClient = Stomp.over(socket);

        stompClient.connect({}, onConnected, onError);
    }
    event.preventDefault();
}


function onConnected() {
    // Subscribe to the Public Topic
    stompClient.subscribe('/topic/public', onMessageReceived);

    // Tell your username to the server
    stompClient.send("/app/chat.addUser",
        {},
        JSON.stringify({sender: username, type: 'JOIN'})
    )

    connectingElement.classList.add('hidden');
}


function onError(error) {
    connectingElement.textContent = 'Could not connect to WebSocket server. Please refresh this page to try again!';
    connectingElement.style.color = 'red';
}


function sendMessage(event) {
    var messageContent = messageInput.value.trim();
    if(messageContent && stompClient) {
        var chatMessage = {
            sender: username,
            content: messageInput.value,
            type: 'CHAT'
        };
        stompClient.send("/app/chat.sendMessage", {}, JSON.stringify(chatMessage));
        messageInput.value = '';
    }
    event.preventDefault();
}


function onMessageReceived(payload) {
    var message = JSON.parse(payload.body);

    var messageElement = document.createElement('li');

    if(message.type === 'JOIN') {
        messageElement.classList.add('event-message');
        message.content = message.sender + ' joined!';
    } else if (message.type === 'LEAVE') {
        messageElement.classList.add('event-message');
        message.content = message.sender + ' left!';
    } else {
        messageElement.classList.add('chat-message');

        var avatarElement = document.createElement('i');
        var avatarText = document.createTextNode(message.sender[0]);
        avatarElement.appendChild(avatarText);
        avatarElement.style['background-color'] = getAvatarColor(message.sender);

        messageElement.appendChild(avatarElement);

        var usernameElement = document.createElement('span');
        var usernameText = document.createTextNode(message.sender);
        usernameElement.appendChild(usernameText);
        messageElement.appendChild(usernameElement);
    }

    var textElement = document.createElement('p');
    var messageText = document.createTextNode(message.content);
    textElement.appendChild(messageText);

    messageElement.appendChild(textElement);

    messageArea.appendChild(messageElement);
    messageArea.scrollTop = messageArea.scrollHeight;
}


function getAvatarColor(messageSender) {
    var hash = 0;
    for (var i = 0; i < messageSender.length; i++) {
        hash = 31 * hash + messageSender.charCodeAt(i);
    }
    var index = Math.abs(hash % colors.length);
    return colors[index];
}

usernameForm.addEventListener('submit', connect, true)
messageForm.addEventListener('submit', sendMessage, true)
```



## 参考サイト
[Spring boot & WebSockets: Build a Real-Time Chat App From Scratch](https://www.youtube.com/watch?v=TywlS9iAZCM)
[IT用語辞典](https://e-words.jp/w/WebSocket.html)