The principles and basic knowledge of WebSocket to implement Java background message push

1. What is WebSocket

The WebSocket protocol is a new network protocol based on TCP. It implements full-duplex communication between the browser and the server - allowing the server to proactively send information to the client.

2. Implementation Principle

In the process of implementing websocket connection, a websocket connection request needs to be sent through the browser, and then the server sends a response. This process is usually called "handshake". In the WebSocket API, the browser and the server only need to perform a handshake action, and then a fast channel is formed between the browser and the server. Data can be transmitted directly between the two.

3. Advantages

In the previous message push mechanism, Ajax polling was used, and the browser automatically issued a request at a specific time interval. The server's messages are actively pulled back. This method consumes a lot of resources because it is essentially an HTTP request and is very clumsy. WebSocket completes a handshake between the browser and the server. After the connection is established, the server can actively transmit data to the client, and the client can also send data to the server at any time.

4.The difference between WebSocket and Socket

　1.WebSocket:

1. ##The establishment phase of websocket communication relies on the http protocol. The initial handshake phase is the http protocol. After the handshake is completed, it switches to the websocket protocol and is completely separated from the http protocol.

2. When establishing communication, the client actively initiates a connection request and the server passively listens.

Once the communication connection is established, the communication is in "full-duplex" mode. In other words, both the server and the client can send data freely at any time, which is very suitable for business scenarios where the server wants to actively push real-time data.
3. 
   

4. The interaction mode is no longer the "request-response" mode, and the communication protocol is completely designed by the developer.

   
   

5. The communication data is based on "frame", which can transmit text data or binary data directly, with high efficiency. Of course, developers also have to consider technical details such as packaging, unpacking, and numbering.

　2.Socket:

6. The server monitors communication and passively provides services; the client actively initiates a connection request to the server, Communication is established.

7. Every interaction is: the client actively initiates a request (request), and the server passively responds (response).

The server cannot actively push data to the client.
8. 
   

9. #The communication data is based on text format. Binary data (such as pictures, etc.) must be converted into text using base64 and other means before it can be transmitted.

   
   

5.WebSocket client:

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var websocket = null; var host = document.location.host; var username = "${loginUsername}"; // Get the userName of the currently logged in person // alert(username) //Determine whether the current browser supports WebSocket if ('WebSocket' in window) { alert("The browser supports Websocket") websocket = new WebSocket('ws://' host '/mm-dorado/webSocket/' username); } else { alert('Current browser Not support websocket') } //Callback method for connection errors websocket.onerror = function() { 　alert("WebSocket connection error") setMessageInnerHTML("WebSocket connection error"); }; //Callback method for successful connection establishment websocket.onopen = function() { 　alert("WebSocket connection successful") setMessageInnerHTML("WebSocket connection successful"); } //Callback method for receiving message websocket.onmessage = function(event) { alert("Callback method of receiving message") alert("This is the message pushed in the background:" event.data); websocket.close(); 　　alert("webSocket has been closed!") } //Callback method for connection closing websocket.onclose = function() { setMessageInnerHTML("WebSocket connection closed"); } //Listen to the window closing event. When the window is closed, actively close the websocket connection to prevent the window from closing before the connection is disconnected. The server will throw an exception. window.onbeforeunload = function() { closeWebSocket(); } //Close WebSocket connection function closeWebSocket() { websocket.close(); } //Display the message on the web page function setMessageInnerHTML(innerHTML) {        document.getElementById('message').innerHTML = innerHTML '<br/>' ; }

6. WebSocket server (java background):

1. Core class:

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package com.mes.util; import java.io.IOException; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import javax.websocket.OnClose; import javax.websocket.OnError; import javax.websocket.OnMessage; import javax.websocket.OnOpen; import javax.websocket.Session; import javax.websocket.server.PathParam; import javax.websocket.server.ServerEndpoint; import org.springframework.stereotype.Component; import org.springframework.stereotype.Service; import com.google.gson.JsonObject; import net.sf.json.JSONObject; @ServerEndpoint("/webSocket/{username}") public class WebSocket {        private static int onlineCount = 0;        private static Map<String, WebSocket> clients = new ConcurrentHashMap<String , WebSocket>();         private Session session;         private String username; <p><code>                                                                             @OnOpen       public void onOpen(@PathParam(" username") String username, Session session) throws IOException {                        this.username = username;            this.session = session;                                                                              addOnlineCount(); <p><code>            clients.put(username, this); <p><code>            System.out.println("已连接");         }                  @OnClose          public void onClose() throws IOException {  <p><code>            clients.remove(username);  <p><code>            subOnlineCount();          }                  @OnMessage          public void onMessage(String message) throws IOException {          <p><code>            JSONObject jsonTo = JSONObject.fromObject(message);  <p><code>            String mes = (String) jsonTo.get("message"); <p><code>              <p><code>            if (!jsonTo.get("To").equals("All")){  <p><code>                sendMessageTo(mes, jsonTo.get("To").toString());  <p><code>            }else{  <p><code>                sendMessageAll("给所有人");  <p><code>            }          }                  @OnError          public void onError(Session session, Throwable error) {  <p><code>            error.printStackTrace();          }                  public void sendMessageTo(String message, String To) throws IOException {  <p><code>            // session.getBasicRemote().sendText(message);  <p><code>            //session.getAsyncRemote().sendText(message);  <p><code>            for (WebSocket item : clients.values()) {  <p><code>                if (item.username.equals(To) )  <p><code>                    item.session.getAsyncRemote().sendText(message);  <p><code>            }          }                      public void sendMessageAll(String message) throws IOException {  <p><code>            for (WebSocket item : clients.values()) {  <p><code>                item.session.getAsyncRemote().sendText(message);  <p><code>            }          }                  public static synchronized int getOnlineCount() {  <p><code>            return onlineCount;          }                  public static synchronized void addOnlineCount() {  <p><code>            WebSocket.onlineCount ;          }                  public static synchronized void subOnlineCount() {  <p><code>            WebSocket.onlineCount--;          }                  public static synchronized Map<String, WebSocket> getClients() {  <p><code>            return clients;          }  }

　　2.在自己代码中的调用：

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WebSocket ws = new WebSocket(); JSONObject jo = new JSONObject(); jo.put("message", "这是后台返回的消息！"); jo.put("To",invIO.getIoEmployeeUid()); ws.onMessage(jo.toString());

　　7.所需maven依赖：

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<!-- webSocket 开始--> <dependency>     <groupId>javax.websocket</groupId>     <artifactId>javax.websocket-api</artifactId>     <version>1.1</version>     <scope>provided</scope> </dependency>   <dependency>     <groupId>javax</groupId>     <artifactId>javaee-api</artifactId>     <version>7.0</version>     <scope>provided</scope> </dependency> <!-- webSocket 结束-->

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