background

Past articles: https://qiita.com/take4eng/items/d0b009c48ee8c3fe420a

As described in the previous article above, create a server program in Java and perform socket communication. ⇒Since HTTP communication is analyzed by pushing it, the code is uselessly complicated.

There are many APIs related to socket communication in Java EE, and it is very easy to implement. Many people have already summarized it, but I will summarize the implementation contents.

Even though a convenient API is prepared, no one does analysis by pushing it. Even if I google it, it doesn't come out easily ...

Practical content

How to use WebSocket API
Create a server program using the API
Edit the client program code in the past article to create a chat application

How to use WebSocket API

Describes the basic WebSocket API. There are many APIs other than those introduced here, but you can google if necessary.

Creating an Endpoint class

import javax.websocket.server.ServerEndpoint;
 
@ServerEndpoint("/Context path")
public class SanpleEndpoint {
}

Import the ServerEndpoint class
Annotate the class with @ServerEndpoint
Write a context path that indicates the location of the file

Creating a processing method

/*
Import each class
import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
*/

//Processing when connecting to a client
@OnOpen
public void onOpen(Session session) {
}
 
//What to do when a message is received from a client
@OnMessage
public void onMessage(String message) {
}

//What to do when an error occurs
@OnError
public void onError(Throwable error) {
}

//What to do when the connection with the client is lost
@OnClose
public void onClose(Session session) {
}

Import the required classes
Add each annotation corresponding to the method
Arguments can be changed or added as needed

Create a server program using API

`Server program`


import java.io.IOException;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;

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

//Annotation that indicates that it is a server-side class of WebSocket.
//argument(wSck)Represents the URI used when connecting from the client.
@ServerEndpoint(value = "/wSck")
public class SocketFree2 {

	//Create a client session thread(Save each session for each client)
	//Set: Collection with no duplicate elements
	//CopyOnWriteArrayList：java.util.A thread-safe version of Set
	private static Set<Session> user = new CopyOnWriteArraySet<>();

	@OnOpen//When connecting with a client
    public void onOpen(Session mySession) {
        System.out.println("connect ID:"+mySession.getId());//session.getId():Get session ID
        user.add(mySession);//Add session for each client to list
    }

    @OnMessage//When data is sent from the client
    public void onMessage(String text , Session mySession) {//The arguments are the text sent and the session from which it originated.
    	System.out.println(text);
    	//getAsyncRemote(): Get an instance of RemoteEndpoint
    	//sendText(String): Send text to client
    	for (Session user : user) {
    		user.getAsyncRemote().sendText(text);
            System.out.println(user.getId()+"Second"+mySession.getId()+"I sent the second message!");
    	}
    	if(text.equals("bye")) onClose(mySession);//Disconnect if text is "bye"
    }

    @OnClose//When the client disconnects
    public void onClose(Session mySession) {
    	System.out.println("disconnect ID:"+mySession.getId());
        user.remove(mySession);//Remove disconnected client session from list
        try {
			mySession.close();//Disconnect with close method
		} catch (IOException e) {
			System.err.println("An error has occurred: " + e);
		}
    }

}

Code description

1. Add Endpoint annotation @ServerEndpoint to class and describe context path @ServerEndpoint(value = "/wSck")
Create a list that identifies each client private static Set<Session> user = new CopyOnWriteArraySet<>();
1. onOpen method: Add client session to list user.add(mySession);

Four. onMessage method: Send the received text to the client as it is ⇒ Send to all clients connected by for statement user.getAsyncRemote().sendText(text);

Five. onClose method: delete the disconnected client 5-1. Remove from user list: ʻuser.remove (mySession); 5-2. Delete session and disconnect:mySession.close ();`

Execution result

Change the address of the client program and execute it with a web browser.

Refer to past articles for code content var wSck = new WebSocket ("ws: // localhost: 8080 / project name / context path "); (This time " ws: // localhost: 8080 / freeWeb2 / wSck ")

A chat application that displays the sent contents is completed. It also supports access from multiple browsers.

Impressions

Socket communication was very easy to do by using the API. Compared to the one described in the past article, the amount of code written is about 1/4. It's amazing. Super easy.

Besides, it seems that encoding, decoding processing and handling of json data can be done easily. I haven't used it this time, but it will be necessary for full-scale development. See the reference page for details.

Reference page

http://dukelab.hatenablog.com/entry/2014/02/23/145656
https://cloudear.jp/blog/?p=2053
https://qiita.com/opengl-8080/items/7ca8484c8579d264e239

Socket communication with a web browser using Java and JavaScript ②