2018-04-01发表2022-06-17更新Spring / Spring MVC3 分钟读完 (大约480个字)

Spring MVC Servlet 3.0+ 异步方法实现服务端的消息推送

Servlet 3.0+ 异步方法实现服务端消息推送是通过使用定时任务，定时的让控制器从另外一个线程返回一个DeferedResult并推送给客户端。而更新DeferedResult是在使用@Scheduled定时任务注解的方法里执行的。

示例

Maven管理的项目，pom.xml添加Servlet 3.0+版本依赖包。

在SpringMvcConfig.java类上添加开启定时任务的注解

@Configuration
@EnableWebMvc
@EnableScheduling//开启计划任务
@ComponentScan(basePackages = {"com"})
public class SpringMvcConfig extends WebMvcConfigurerAdapter {
	
	/**
	 * 配置viewResolver，用来映射来物理路径
	 * @return
	 */
	@Bean
	public InternalResourceViewResolver viewResolver() {
		InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();

		viewResolver.setPrefix("/WEB-INF/jsp/");
		viewResolver.setSuffix(".jsp");
		viewResolver.setViewClass(JstlView.class);
		return viewResolver;
	}

Web初始化类时添加开启Servlet3.0+异步方法

/**
 * WebApplicationInitializer是Spring提供用来配置Servlet+3.0配置的接口，从而实现了替代web.xml的位置。
 * 实现该接口会自动被SpringServletContainerInitializer(用来启动Servlet3.0容器)获取到。
 * @author Rocky
 *
 */

public class WebInitializer implements WebApplicationInitializer {

	@Override
	public void onStartup(ServletContext servletContext) throws ServletException {
		
		//注解方式配置的web上下文
		AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
		context.register(SpringMvcConfig.class);
		//将上下文和当前servletContext关联
		context.setServletContext(servletContext);
		//注册dispatcher
		Dynamic servlet = servletContext.addServlet("dispatcher", new DispatcherServlet(context));
		servlet.addMapping("/");
		servlet.setLoadOnStartup(1);
		//Servlet3.0支持开启异步方法
		servlet.setAsyncSupported(true);
	}
}

Controller

@Controller
public class AysncController {

	@Autowired
	PushServiceImpl pushServiceImpl;
	
	@RequestMapping("/async")
	public String asyncPage() {
		return "async";
	}

	@RequestMapping("/defer")
	@ResponseBody
	public DeferredResult<String> deferredCall() {
		return pushServiceImpl.getAsyncUpdate();
	}
}

Service

@Service
public class PushServiceImpl {
	
	private DeferredResult<String> deferredResult;
	
	public DeferredResult<String> getAsyncUpdate(){
		deferredResult = new DeferredResult<>();
		return deferredResult;
	}
	
	//定时任务，每5秒执行一次
	@Scheduled(fixedDelay = 5000)
	public void refresh() {
		
		if(deferredResult != null) {
			SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			String dateTime = sdf.format(System.currentTimeMillis());
			deferredResult.setResult("NowDateTime: " + dateTime);
		}
	}
}

jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<script type="text/javascript"
	src="${pageContext.request.contextPath}/static/js/jquery-1.11.0.js"></script>

<script type="text/javascript">
	var s = '';
	deferred();
	
	function deferred() {
		
		$.get('defer', function(data) {
			console.log(data);
			s = s + (data + "<br/>");
			$("#msgFromPush").html(s);
			deferred();
		})
	}
</script>

<title>SSE Demo</title>
</head>
<body>
	<div id="msgFromPush"></div>
</body>
</html>