How to write webSockets for Rest calls in Spring-boot?

Question

I'm new to web socket programming. I have more than 10 methods annotated with @GetMapping, where the returned data is read from a MySQL database.

Can anyone help me to know how to write WebSockets.

My WebRestController.java looks like the below:

@CrossOrigin(origins = "http://localhost:4200", allowedHeaders="*")
@RestController
@RequestMapping("/api")
public class WebRestController {
    @GetMapping("/summary")
    public String Summary() { /* ... */}
    @GetMapping("/erday")
    public String Erday(String erday) { /* ... */}
    @GetMapping("/count")
    public String Count(@RequestParam Map<String,String> queryParam, 
        String date, String target) { /* ... */}
    @GetMapping("/details")
    public String Details(@RequestParam Map<String,String> queryParam, 
        String date, String target) { /* ... */}
    @GetMapping("/devmawah")
    public String DevMawah(@RequestParam Map<String,String> queryParam, 
        String date, String target) { /* ... */}
    // ....
}

I tried before many times in internet to find the solution, but couldn't find it. All I found are examples for Chat applications, which have 2 endpoints to send and receive.

Answer 1

WebSockets are used for bi-directional communication, not really for REST style services (where HTTP is superior in my opinion). The core difference being that HTTP is fundamentally a request-reply protocol, which fits very well to REST whereas WebSocket is centred around messages. Of course, you can argue that request-reply is a specialisation of message-based communication.

There are several articles on this topic (google REST over WebSocket) and even some StackOverflow questions which detail the pros and cons, for example Is ReST over websockets possible?.

The only way that I know of which allows you to do something resembling REST over WebSocket without having to re-write the RestController is swagger-socket, but I would not recommend using it as the project seems to be inactive now and it seems to not have been used extensively.

Alternatively, you can replace your @RequestMapping or @GetMapping annotations with @MessageMapping annotations and model your API through messages (e.g. the client sends a "GET" message to a given destination, and you send back a message containing the resources).