springboot websocket achieve active push messages to the client

pom.xml:

	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.2.2.RELEASE</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-websocket</artifactId>
		</dependency>

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-test</artifactId>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.junit.vintage</groupId>
					<artifactId>junit-vintage-engine</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
	</dependencies>

	@Controller
public class GreetingController {

	private SimpMessagingTemplate template;

	@Autowired
	public GreetingController(SimpMessagingTemplate template) {
		this.template = template;
	}

    /**
    	调用该方法将想客户端推送一次消息
    */
	public void greet(String greeting) {
		this.template.convertAndSend("/topic/greetings", greeting);
	}

}

WebSocket Support
Using WebSocket to build an interactive web application