Daily blog-Server-Sent Events push technology

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overview

SSE (Server-Sent Events) is an HTTP-based server push technology that allows the server to push data to the client in real time. Compared with traditional polling or long polling techniques, SSE has lower latency, higher efficiency and lower resource consumption.

SSE was first introduced by the HTML5 specification, and has been widely used in various Web applications, such as instant messaging, stock quotes, and news information. The working principle of SSE is very simple. The client establishes a long connection with the server (that is, the HTTP connection will not be closed), the server can push data to the client at any time, and the client obtains data by listening to events on this connection .

The advantages of SSE mainly include the following aspects:

1. Good real-time performance: SSE can push data in real time, and can transmit data to the client faster than polling or long polling.

2. Resource saving: SSE only needs to establish a long connection, and does not need to establish and close connections frequently. Compared with traditional polling or long polling technology, it can save server and client resources.

3. High reliability: SSE uses the HTTP protocol for communication, which has good compatibility and stability, and also has an automatic reconnection mechanism, which can automatically reconnect when the network is abnormal.

4. Ease of use: The implementation of SSE is very simple, only need to use the built-in EventSource object of the browser to realize the real-time push of data.

In addition to the above advantages, SSE also has the following characteristics:

1. One-way communication: SSE can only push data from the server to the client, but the client cannot send data to the server.

2. Text data: SSE only supports the transmission of text data and cannot transmit binary data.

3. Stateless: SSE is a stateless protocol, that is, the complete HTTP response header needs to be resent every time data is pushed.

When using SSE, you need to pay attention to the following points:

1. Browser Compatibility: Although SSE has become part of the HTML5 specification, not all browsers support SSE. When using SSE, you need to pay attention to browser compatibility issues.

2. Server implementation: SSE requires the server to implement the logic of pushing data, and issues such as thread safety and concurrency need to be considered during implementation.

3. Data format: SSE only supports the transmission of text data, so the data needs to be converted into a string format when transmitting data.

In short, SSE is a very practical server push technology and has broad application prospects in Web applications. When using SSE, you need to pay attention to issues such as browser compatibility, server implementation, and data format, as well as security and stability.

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SSE VS WS

Both SSE (Server-Sent Events) and WebSocket are technologies that enable the server to push data to the client, but they differ in implementation, application scenarios, and performance.

1. Implementation method

SSE is a technology based on the HTTP protocol, which uses HTTP connections to push data to the client. The client opens an HTTP connection, and then the server can continuously send data to the client through the connection. SSE uses one-way communication, that is, only the server can send data to the client, and the client cannot send data to the server.

WebSocket is a full-duplex communication protocol. After the connection is established, the client and server can send data to each other. WebSocket uses a TCP connection, which is an independent protocol unlike the HTTP protocol.

2. Application scenarios

SSE is suitable for scenarios that require real-time data push, such as stock quotes and chat rooms. Since SSE uses the HTTP protocol, it can use the cache mechanism of HTTP to improve performance. In addition, SSE can also automatically reconnect by setting the retry field to ensure the stability of the connection.

WebSocket is suitable for scenarios that require two-way communication, such as online games, video conferencing, etc. Since WebSocket uses a TCP connection, the stability and reliability of data transmission can be guaranteed.

In addition, WebSocket also supports binary data transmission, which can be used to transmit large files such as audio and video.

3. Performance

There is also a difference between SSE and WebSocket in terms of performance. Since SSE uses the HTTP protocol, an HTTP connection needs to be re-established every time data is sent, which causes additional overhead. In addition, since SSE can only send data from the server to the client, bidirectional communication is not possible.

WebSocket does not have these problems. It uses a TCP connection, which can maintain a long connection and avoid the overhead of establishing a connection each time. In addition, since WebSocket supports two-way communication, real-time interaction between the client and the server is possible.

Four. Summary

Both SSE and WebSocket are technologies that enable the server to push data to the client, but they differ in implementation, application scenarios, and performance.

SSE is suitable for scenarios that need to push data in real time, while WebSocket is suitable for scenarios that require two-way communication.

In terms of performance, WebSocket is better and can maintain long connections and real-time interaction. Therefore, when choosing a technology, you need to choose according to your specific needs.

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Code

The need for real-time data is increasingly common in modern web applications. Although traditional Ajax polling and long polling technologies can realize real-time data update, they all have some disadvantages, such as high server load and high delay. The SSE (Server-Sent Events) technology is a more efficient real-time data update method.

SSE is a server push technology based on the HTTP protocol. It allows the server to push data to the client without requiring the client to initiate a request. SSE uses a long connection, and the server can send data to the client at any time to achieve real-time updates.

The SSE protocol defines a special HTTP response format called "text/event-stream". By subscribing to this special HTTP response, the client can receive the data pushed by the server. SSE also supports features such as event types and annotations to better organize and parse push data.

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Using SSE with Spring Boot

Using SSE with Spring Boot is very simple. First, we need to add a dependency:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

We use webflux, plus a

  <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-webflux</artifactId>
  </dependency>

Then, add a @RequestMapping annotation to our Controller and specify the produces attribute as "text/event-stream":

@RestController
public class SSEController {
    
    

    @RequestMapping(value = "/sse", produces = "text/event-stream")
    public ResponseEntity<Flux<String>> sse() {
    
    
        Flux<String> flux = Flux.interval(Duration.ofSeconds(1)).map(i -> "message " + i);
        return ResponseEntity.ok().body(flux);
    }
}

The code above defines a route called "/sse" which returns a Flux object. Flux is a reactive stream that can generate an unlimited number of elements with a specified time interval between each element. In the above example, we send a message every 1 second.

Finally, we need to subscribe to this route on the client side to receive the data pushed by the server. In JavaScript, you can use the EventSource object to subscribe to SSE:

var eventSource = new EventSource('/sse');
eventSource.onmessage = function(event) {
    
    
    console.log('Received message: ' + event.data);
};

The code above creates an EventSource object and subscribes to the "/sse" route. When the server pushes a message, the onmessage callback function will be triggered and the received message will be printed.

The entire code of index is as follows

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>SSE-DEMO</title>
</head>
<body>

<h1>SSE - Flux</h1>
<div id="sse-flux"></div>

<script>
    const eventSource = new EventSource('/sse');
    eventSource.onmessage = function (event) {
      
      
        document.getElementById("sse-flux").innerHTML = event.data;
        console.log('Received message: ' + event.data);
    };
</script>
</body>
</html>

test

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Summarize

We introduced how to use SSE technology in Spring Boot to achieve real-time data updates. SSE is a very efficient and easy-to-use server push technology, which can greatly improve the real-time performance of web applications. When using SSE, we need to define a route and return a Flux object. The client can subscribe to this route through the EventSource object and receive the data pushed by the server.

If you are developing a web application that requires real-time data updates, you may wish to consider using SSE technology to achieve it. It can make applications more efficient, fast and reliable.