When working with A Web framework, you can’t avoid dealing with these concepts, so let’s wrap things up and go through interceptors, filters, listeners.
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1. Differences between interceptors, filters, and listeners
- Interceptor: Depends on the Web framework, based on Java reflection mechanism, belongs to a kind of AOP application. An interceptor instance can be called multiple times during a controller life cycle. Only Controller requests can be intercepted.
- Filters: Rely on the Servlet container, based on function callback, can be filtered for almost any request, a Filter instance can only be invoked once in the container initialization.
- Listeners: Web listeners are special classes in servlets that listen for specific events on the Web. They are started with the Web application and initialized only once.
2. What’s the use
- Interceptor: When a request is in progress, you want to interfere with its progress and even control whether it is terminated. That’s what interceptors do.
- Filter: When you have a bunch of things, you only want to select the things that fit. The tool that defines these requirements is the filter.
- Listener: After an event occurs, you only want to obtain the details of the occurrence of the event without interfering with the execution of the event
3. Startup sequence
Listener > Filter > InterceptorCopy the code4. Specific implementation in SpringBoot
(1) Interceptor
- Interceptors are commonly implemented in two ways
- Implement the HandlerInterceptor interface
- Inheritance HandlerInterceptorAdapter abstract classes
- Distinction and connection
- HandlerInterceptorAdapter AsyncHandlerInterceptor interface, AsyncHandlerInterceptor interface inheritance HandlerInterceptor interface.
- More than a afterConcurrentHandlingStarted method AsyncHandlerInterceptor interface
- The specific methods
- PreHandle // The first method to go after the request returns true to continue execution
- PostHandle // request after return before
- AfterCompletion // After processing is complete
- AfterConcurrentHandlingStarted / / if it returns a current type of variable, will enable a new thread. Immediately after execution preHandle method will be called afterConcurrentHandlingStarted, and then a new thread successively performed preHandle, postHandle, afterCompletion
- Code implementation
The following code is based on springboot2.0
(1) the interceptor
MyInterceptor1 inheritance HandlerInterceptorAdapter
MyInterceptor2 implements the HandlerInterceptor interface
public class MyInterceptor1 extends HandlerInterceptorAdapter {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
request.setAttribute("startTime", System.currentTimeMillis());
System.out.println(">>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>>");
return super.preHandle(request, response, handler);
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
long startTime = (long) request.getAttribute("startTime");
System.out.println("MyInterceptor1 execution." + (System.currentTimeMillis() - startTime));
System.out.println(">>>>> MyInterceptor1 postHandle >>>>>>>>>>>>>>>>>>>>>>");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
request.removeAttribute("startTime");
System.out.println(">>>>> MyInterceptor1 afterCompletion >>>>>>>>>>>>>>>>>>>>>>");
}
@Override
public void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
super.afterConcurrentHandlingStarted(request, response, handler);
System.out.println(">>>>> MyInterceptor1 afterConcurrentHandlingStarted >>>>>>>>>>>>>>>>>>>>>>"); }}Copy the codepublic class MyInterceptor2 implements HandlerInterceptor {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
request.setAttribute("startTime", System.currentTimeMillis());
System.out.println(">>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>>");
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
long startTime = (long) request.getAttribute("startTime");
System.out.println("MyInterceptor2 execution." + (System.currentTimeMillis() - startTime));
System.out.println(">>>>> MyInterceptor2 postHandle >>>>>>>>>>>>>>>>>>>>>>");
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
request.removeAttribute("startTime");
System.out.println(">>>>> MyInterceptor2 afterCompletion >>>>>>>>>>>>>>>>>>>>>>"); }}Copy the code(2) configuration
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new MyInterceptor1()).addPathPatterns("/ * *");
registry.addInterceptor(new MyInterceptor2()).addPathPatterns("/ * *"); }}Copy the code(3) request
@RestController
@SpringBootApplication
public class SpringbootInterceptorApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbootInterceptorApplication.class, args);
}
@GetMapping(value = "/hello1")
public ResponseEntity<String> hello(a) throws InterruptedException {
Thread.sleep(500);
return ResponseEntity.ok("HelloWorld");
}
@GetMapping(value = "/hello2")
public StreamingResponseBody hello2(a) throws InterruptedException {
Thread.sleep(500);
return (OutputStream outputStream) -> {
outputStream.write("success".getBytes());
outputStream.flush();
outputStream.close();
};
}
@GetMapping(value = "/hello3")
public Future<String> hello3(a) throws InterruptedException {
Thread.sleep(500);
return new AsyncResult<>("Hello"); }}Copy the code(4) Running results
-
Request/hello1
>>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>> MyInterceptor2 :516 >>>>> MyInterceptor2 postHandle >>>>>>>>>>>>>>>>>>>>> MyInterceptor1 :516 >>>>> MyInterceptor1 postHandle >>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor2 afterCompletion >>>>>>>>>>>>>>>> >>>>> MyInterceptor1 afterCompletion >>>>>>>>>>>>>>>>Copy the codeTo execute, press preHandle > postHandle > afterCompletion
-
Request /hello2 or /hello3
>>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor1 afterConcurrentHandlingStarted >>>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor1 preHandle > > > > > > > > > > > > > > > > > > > > > > > > > > > MyInterceptor2 preHandle > > > > > > > > > > > > > > > > > > > > > > MyInterceptor2 execution: 1 > > > > > MyInterceptor2 PostHandle > > > > > > > > > > > > > > > > > > > > > > MyInterceptor1 execution: 1 > > > > > MyInterceptor1 postHandle > > > > > > > > > > > > > > > > > > > > > > > > > > > MyInterceptor2 afterCompletion >>>>>>>>>>>>>>>>>>>>>> >>>>> MyInterceptor1 afterCompletion >>>>>>>>>>>>>>>>>>>>>>Copy the codeMyInterceptor1 execution order preHandle > afterConcurrentHandlingStarted > preHandle > postHandle > afterCompletion
MyInterceptor2 Order of execution preHandle > preHandle > postHandle > afterCompletion
For a return value of a Concurrent type, Spring starts a new thread to process the concurrent message, in which the preHandle method is called again.
(2) filter
(1) filter
public class MyFilter1 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println(filterConfig.getInitParameter("initParam"));
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("doFilter1 >>>>>>>>>>>"); filterChain.doFilter(servletRequest, servletResponse); }}Copy the code(2) configuration
- The first way
@Bean
public FilterRegistrationBean<MyFilter1> filterRegistrationBean(a) {
FilterRegistrationBean<MyFilter1> filterRegistrationBean = new FilterRegistrationBean<>();
filterRegistrationBean.addUrlPatterns("/ *");// Filter all
filterRegistrationBean.setFilter(new MyFilter1());
filterRegistrationBean.setOrder(1);
filterRegistrationBean.addInitParameter("initParam"."initOk");
return filterRegistrationBean;
}
Copy the code- The second way
@Bean
public MyFilter1 myFilter(a) {
return new MyFilter1();
}
Copy the code- The third way
@WebFilter("/test/*")
public class MyFilter2 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("MyFilter2");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
filterChain.doFilter(servletRequest, servletResponse);
System.out.println("DoFilter 2"); }}Copy the code@servletComponentScan (“com.jiuxian”) ¶
Note that the configuration of Filter global Interceptor(/*) is different from that of Interceptor(/**)
(3) Listener
(1) the listener
public class MyListener1 implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("MyListener1 ... "); }}Copy the code(2) The configuration mode is similar to Filter
- The first way
@Bean
public ServletListenerRegistrationBean<MyListener1> registrationBean(a) {
ServletListenerRegistrationBean<MyListener1> servletListenerRegistrationBean
= new ServletListenerRegistrationBean<>();
servletListenerRegistrationBean.setListener(new MyListener1());
return servletListenerRegistrationBean;
}
Copy the code- The second way
@Bean
public MyListener1 myListener1(a) {
return new MyListener1();
}
Copy the code- The third way
@WebListener
public class MyListener2 implements ServletRequestListener {
@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("MyListener2"); }}Copy the codeTo use the @webListener annotation, you first need @ServletComponentScan(“com.jiuxian”).
[note] the above code is based on springboot2.0
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