SpringBoot 拦截器、过滤器、监听器

  在工作中使用Web框架，总是避免不了与这些概念打交道，做一下总结，一口气说完拦截器、过滤器、监听器。

GitHub源码地址

1. 拦截器、过滤器、监听器区别

• 拦截器(interceptor)：依赖于web框架，基于Java的反射机制，属于AOP的一种应用。一个拦截器实例在一个controller生命周期内可以多次调用。只能拦截Controller的请求。
• 过滤器(Filter)：依赖于Servlet容器，基于函数回掉，可以对几乎所有请求过滤，一个过滤器实例只能在容器初使化调用一次。
• 监听器(Listener)：web监听器是Servlet中的特殊的类，用于监听web的特定事件，随web应用启动而启动，只初始化一次。

2. 有什么用

• 拦截器(interceptor)：在一个请求进行中的时候，你想干预它的进展，甚至控制是否终止。这是拦截器做的事。
• 过滤器(Filter)：当有一堆东西，只希望选择符合的东西。定义这些要求的工具，就是过滤器。
• 监听器(Listener)：一个事件发生后，只希望获取这些事个事件发生的细节，而不去干预这个事件的执行过程，这就用到监听器

3. 启动顺序

监听器 >  过滤器 > 拦截器

4.SpringBoot中的具体实现

（1） 拦截器

1. 拦截器常用有两种方式实现
   实现HandlerInterceptor接口
   • 继承HandlerInterceptorAdapter 抽象类
2. 区别和联系

• HandlerInterceptorAdapter 实现AsyncHandlerInterceptor接口，AsyncHandlerInterceptor接口 继承HandlerInterceptor接口.
• AsyncHandlerInterceptor接口多了一个afterConcurrentHandlingStarted方法

1. 具体方法

• preHandle //请求过来之后首先走的方法 return true 继续往下执行
• postHandle //请求之后返回之前
• afterCompletion //处理完成之后
• afterConcurrentHandlingStarted //如果返回一个current类型的变量，会启用一个新的线程。执行完preHandle方法之后立即会调用afterConcurrentHandlingStarted,然后新线程再以次执行preHandle,postHandle,afterCompletion

1. 代码实现

【注】以下代码基于springboot2.0

(1)拦截器

MyInterceptor1 继承 HandlerInterceptorAdapter

MyInterceptor2 实现 HandlerInterceptor接口

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 执行:" + (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 >>>>>>>>>>>>>>>>>>>>>>");
}
}

public 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 执行:" + (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 >>>>>>>>>>>>>>>>>>>>>>");
}
}

(2)配置

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new MyInterceptor1()).addPathPatterns("/**");
registry.addInterceptor(new MyInterceptor2()).addPathPatterns("/**");
}
}

(3)请求

@RestController
@SpringBootApplication
public class SpringbootInterceptorApplication {

public static void main(String[] args) {
SpringApplication.run(SpringbootInterceptorApplication.class, args);
}

@GetMapping(value = "/hello1")
public ResponseEntity<String> hello() throws InterruptedException {
Thread.sleep(500);
return ResponseEntity.ok("HelloWorld");
}

@GetMapping(value = "/hello2")
public StreamingResponseBody hello2() throws InterruptedException {
Thread.sleep(500);
return (OutputStream outputStream) -> {
outputStream.write("success".getBytes());
outputStream.flush();
outputStream.close();
};
}

@GetMapping(value = "/hello3")
public Future<String> hello3() throws InterruptedException {
Thread.sleep(500);
return new AsyncResult<>("Hello");
}
}

(4) 运行结果

1. 请求/hello1

   >>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>>
   MyInterceptor2 执行:516
   >>>>> MyInterceptor2 postHandle >>>>>>>>>>>>>>>>>>>>>
   MyInterceptor1 执行:516
   >>>>> MyInterceptor1 postHandle >>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor2 afterCompletion >>>>>>>>>>>>>>>>
   >>>>> MyInterceptor1 afterCompletion >>>>>>>>>>>>>>>>

   执行按preHandle > postHandle > afterCompletion

2. 请求/hello2 或 /hello3

   >>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor1 afterConcurrentHandlingStarted >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor1 preHandle >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor2 preHandle >>>>>>>>>>>>>>>>>>>>>>
   MyInterceptor2 执行:1
   >>>>> MyInterceptor2 postHandle >>>>>>>>>>>>>>>>>>>>>>
   MyInterceptor1 执行:1
   >>>>> MyInterceptor1 postHandle >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor2 afterCompletion >>>>>>>>>>>>>>>>>>>>>>
   >>>>> MyInterceptor1 afterCompletion >>>>>>>>>>>>>>>>>>>>>>

   MyInterceptor1 执行顺序 preHandle > afterConcurrentHandlingStarted > preHandle > postHandle >afterCompletion

   MyInterceptor2 执行顺序 preHandle > preHandle > postHandle > afterCompletion

综上.对于concurrent类型的返回值，spring会启用一个新的线程来处理concurrent类型消息，在新的线程中会重新调用preHandle方法。

（2） 过滤器

(1) 过滤器

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);
}
}

(2) 配置

• 第一种方式

@Bean
public FilterRegistrationBean<MyFilter1> filterRegistrationBean() {
FilterRegistrationBean<MyFilter1> filterRegistrationBean = new FilterRegistrationBean<>();
filterRegistrationBean.addUrlPatterns("/*");//过滤所有
filterRegistrationBean.setFilter(new MyFilter1());
filterRegistrationBean.setOrder(1);
filterRegistrationBean.addInitParameter("initParam", "initOk");
return filterRegistrationBean;
}

• 第二种方式

@Bean
public MyFilter1 myFilter() {
return new MyFilter1();
}

• 第三种方式

@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");
}
}

通过@WebFilter("/test/*")注解，首先需要@ServletComponentScan(“com.jiuxian”)

Filter 全局拦截的配置(/*)和 Interceptor(/**)有所区别需要注意

（3） 监听器

(1) 监听器

public class MyListener1 implements ServletContextListener {

@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("MyListener1 ... ");
}
}

(2) 配置方式和Filter类似

• 第一种方式

@Bean
public ServletListenerRegistrationBean<MyListener1> registrationBean() {
ServletListenerRegistrationBean<MyListener1> servletListenerRegistrationBean
= new ServletListenerRegistrationBean<>();
servletListenerRegistrationBean.setListener(new MyListener1());
return servletListenerRegistrationBean;
}

• 第二种方式

@Bean
public MyListener1 myListener1() {
return new MyListener1();
}

• 第三种方式

@WebListener
public class MyListener2 implements ServletRequestListener {

@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("MyListener2");
}
}

使用@WebListener注解，首先需要@ServletComponentScan(“com.jiuxian”)

【注】以上代码基于springboot2.0

GitHub源码地址