WebSocket的主動推送
關於消息推送，現在的解決方案如輪詢、長連接或者短連接，當然還有其他的一些技術框架，有的是客戶端直接去服務端拿數據。
其實推送推送主要講的是一個推的概念，WebSocket是一種主動推送消息的技術。
基於Java的WebSocket
這里主要是結合網上的例子實現下。
簡單的客戶端JavaScript
<!DOCTYPE html>
<html>
<head>
<title>Testing websockets</title>
</head>
<body>
<div>
<input type="submit" value="Start" onclick="start()" />
</div>
<div id="messages"></div>
<script type="text/javascript">
var webSocket =
new WebSocket('ws://localhost:8080/wesocket/websocketTest');
webSocket.onerror = function(event) {
onError(event)
};
webSocket.onopen = function(event) {
onOpen(event)
};
webSocket.onmessage = function(event) {
onMessage(event)
};
function onMessage(event) {
document.getElementById('messages').innerHTML
+= '<br />' + event.data;
}
function onOpen(event) {
document.getElementById('messages').innerHTML
= 'Connection established';
}
function onError(event) {
alert(event.data);
}
function start() {
webSocket.send('hello');
return false;
}
</script>
</body>
</html>
服務端
package com.tony.websocket;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
@ServerEndpoint("/websocketTest")
public class WebSocketTest {
@OnMessage
public void onMessage(String message, Session session) throws IOException, InterruptedException {
// Print the client message for testing purposes
System.out.println("Received: " + message);
// Send the first message to the client
session.getBasicRemote().sendText("This is the first server message");
// Send 3 messages to the client every 5 seconds
int sentMessages = 0;
while (sentMessages < 3) {
Thread.sleep(5000);
session.getBasicRemote().sendText("This is an intermediate server message. Count: " + sentMessages);
sentMessages++;
}
// Send a final message to the client
session.getBasicRemote().sendText("This is the last server message");
}
@OnOpen
public void onOpen() {
System.out.println("Client connected");
}
@OnClose
public void onClose() {
System.out.println("Connection closed");
}
}
pom.xml 文件
<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.tony</groupId>
<artifactId>wesocket</artifactId>
<version>0.0.1-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>javax.websocket</groupId>
<artifactId>javax.websocket-api</artifactId>
<version>1.0-rc5</version>
<scope>provided</scope>
</dependency>
</dependencies>
</project>
我這里用的是JDK是 jdk1.8.0_60 ，Tomcat用的是 apache-tomcat-7.0.64 。
1、建立連接
2、發送消息
3、服務端推送消息
