背景

公司網站上線需要一個實時報價功能，於是想到了 Websocket， 我在多年前就嘗試過Websocket 那時 HTML5標準尚未產生，各家實現均有不同，Websocket 版本也非常多，實現相容也比較複雜，於是放棄Websocket。最近看到Websocket 開始流行起來，相容也不再是障礙。

以下節選自《Netkiller Java 手札》，下面例子實現一個簡單的 Echo Server

目錄

• 7.1. Server
• 7.2. Client

環境：Java8 + Tomcat8

7.1. Server

package websocket;

/**
 * Websocket Server
 * 
 * @author netkiller<[email protected]>
 */

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint(value = "/echo")
public class PriceServer {

	private Set<Session> sessions = Collections.synchronizedSet(new HashSet<Session>());

	/**
	 * Callback hook for Connection open events. This method will be invoked
	 * when a client requests for a WebSocket connection.
	 * 
	 * @param session
	 *            the session which is opened.
	 */
	@OnOpen
	public void onOpen(Session session) {
		sessions.add(session);
	}

	/**
	 * Callback hook for Connection close events. This method will be invoked
	 * when a client closes a WebSocket connection.
	 * 
	 * @param session
	 *            the session which is opened.
	 */
	@OnClose
	public void onClose(Session session) {
		sessions.remove(session);
	}

	/**
	 * Callback hook for Message Events. This method will be invoked when a
	 * client send a message.
	 * 
	 * @param message
	 *            The text message
	 * @param session
	 *            The session of the client
	 */
	@OnMessage
	public void onMessage(String message, Session session) {
		System.out.println("Message Received: " + message);
		for (Session remote : sessions) {
			System.out.println("Sending to " + remote.getId());
			remote.getAsyncRemote().sendText(message);
		}
	}
}