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
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| @Configuration
@EnableWebMvc
@EnableScheduling
@ComponentScan(basePackages = {"com"})
public class SpringMvcConfig extends WebMvcConfigurerAdapter {
@Bean
public InternalResourceViewResolver viewResolver() {
InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
viewResolver.setPrefix("/WEB-INF/jsp/");
viewResolver.setSuffix(".jsp");
viewResolver.setViewClass(JstlView.class);
return viewResolver;
}
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- Web初始化类时添加开启Servlet3.0+异步方法
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public class WebInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
context.register(SpringMvcConfig.class);
context.setServletContext(servletContext);
Dynamic servlet = servletContext.addServlet("dispatcher", new DispatcherServlet(context));
servlet.addMapping("/");
servlet.setLoadOnStartup(1);
servlet.setAsyncSupported(true);
}
}
|
- Controller
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| @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
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| @Service
public class PushServiceImpl {
private DeferredResult<String> deferredResult;
public DeferredResult<String> getAsyncUpdate(){
deferredResult = new DeferredResult<>();
return deferredResult;
}
@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
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| <%@ 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>
|
参考资料
Servlet 3特性：异步Servlet
tomcat servlet3的异步化原理理解
