Java的Servlet、Filter、Interceptor、Listener

写在前面：

使用Spring-Boot时，嵌入式Servlet容器可以通过扫描注解（@ServletComponentScan）的方式注册Servlet、Filter和Servlet规范的所有监听器（如HttpSessionListener监听器）。

Spring boot 的主 Servlet 为 DispatcherServlet，其默认的url-pattern为“/”。一般情况系统默认的Servlet就够用了，如果需要自定义Servlet，可以继承系统抽象类HttpServlet，重写方法来实现自己的Servlet。关于Servlet、过滤器、拦截器、监听器可以参考：（转）servlet、filter、listener、interceptor之间的区别和联系

Spring-Boot有两种方法注册Servlet、Filter和Listener ：

1、代码注册：通过ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 获得控制。

2、在 SpringBootApplication 上使用@ServletComponentScan 注解后，Servlet、Filter、Listener 可以直接通过 @WebServlet、@WebFilter、@WebListener 注解自动注册，无需其他代码。

一、Servlet

Servlet匹配规则：匹配的优先级是从精确到模糊，复合条件的Servlet并不会都执行。

1、通过@ServletComponentScan自动扫描

a、springboot的启动入口添加注解：@ServletComponentScan；

@SpringBootApplication
@ServletComponentScan
public class ApplicationMain {public static void main(String[] args) {SpringApplication.run(ApplicationMain.class, args);}
}

b、@WebServlet 自定义Servlet，配置处理请求路径 /demo/myServlet

@WebServlet(name = "myServletDemo1",urlPatterns = "/demo/myServlet",description = "自定义的servlet")
public class MyServletDemo1 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("==========myServletDemo Get Method==========");resp.getWriter().println("my myServletDemo1 process request");super.doGet(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("==========myServletDemo1 POST Method==========");super.doPost(req, resp);}
}

2、使用@ServletRegistrationBean注解

a、@ServletRegistrationBean注入自定义的Servlet，配置处理的路径为 /demo/servletDemo2

@Configuration
public class ServletConfiguration {/*** 代码注入*/@Beanpublic ServletRegistrationBean myServletDemo() {return new ServletRegistrationBean(new MyServletDemo2(), "/demo/servletDemo2");}
}

b、自定义的Servlet

public class MyServletDemo2 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("==========myServletDemo2 Get Method==========");resp.getWriter().println("my myServletDemo2 process request");super.doGet(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("==========myServletDemo2 POST Method==========");super.doPost(req, resp);}
}

二、Filter

完整的流程是：Filter对用户请求进行预处理，接着将请求交给Servlet进行处理并生成响应，最后Filter再对服务器响应进行后处理。

Filter有如下几个用处。

在HttpServletRequest到达Servlet之前，拦截客户的HttpServletRequest。
根据需要检查HttpServletRequest，也可以修改HttpServletRequest头和数据。
在HttpServletResponse到达客户端之前，拦截HttpServletResponse。
根据需要检查HttpServletResponse，也可以修改HttpServletResponse头和数据。

多个FIlter可以组成过滤器调用链，按设置的顺序逐一进行处理，形成Filter调用链。

1、通过@ServletComponentScan自动扫描

a、springboot的启动入口添加注解：@ServletComponentScan；

b、@WebFilter 配置处理全部url的Filter

@WebFilter(filterName = "myFilter",urlPatterns = "/*")
public class MyFilter implements Filter {public void init(FilterConfig filterConfig) throws ServletException {System.out.println(">>>>>>myFilter init ……");}public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println(">>>>>>执行过滤操作");filterChain.doFilter(servletRequest, servletResponse);}public void destroy() {System.out.println(">>>>>>myFilter destroy ……");}
}

* doFilter()方法是过滤器的核心方法，实现该方法就可实现对用户请求进行预处理，也可实现对服务器响应进行后处理——它们的分界线为是否调用了filterChain.doFilter()，执行该方法之前，即对用户请求进行预处理；执行该方法之后，即对服务器响应进行后处理。

2、通过@FilterRegistrationBean注册

a、@Bean注入自定义的Filter

@Configuration
public class ServletConfiguration {@Beanpublic FilterRegistrationBean myFilterDemo(){FilterRegistrationBean registration = new FilterRegistrationBean();registration.setFilter(new MyFilter2());registration.addUrlPatterns("/demo/myFilter2");registration.addInitParameter("paramName", "paramValue");registration.setName("myFilter2");registration.setOrder(2);//指定filter的顺序return registration;}
}

b、自定义的Filter

public class MyFilter2 implements Filter {public void init(FilterConfig filterConfig) throws ServletException {System.out.println("======MyFilter2 init ……");}public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("======MyFilter2执行过滤操作");filterChain.doFilter(servletRequest, servletResponse);}public void destroy() {System.out.println("======MyFilter2 destroy ……");}
}

三、Listener

目前 Servlet 中提供了 6 种两类事件的观察者接口，它们分别是：4 个 EventListeners 类型的，ServletContextAttributeListener、ServletRequestAttributeListener、ServletRequestListener、HttpSessionAttributeListener 和 2 个 LifecycleListeners 类型的，ServletContextListener、HttpSessionListener。

ServletContextAttributeListener监听对ServletContext属性的操作，比如增加、删除、修改属性。
ServletContextListener监听ServletContext。当创建ServletContext时，激发contextInitialized(ServletContextEvent sce)方法；当销毁ServletContext时，激发contextDestroyed(ServletContextEvent sce)方法。
HttpSessionListener监听HttpSession的操作。当创建一个Session时，激发session Created(HttpSessionEvent se)方法；当销毁一个Session时，激发sessionDestroyed (HttpSessionEvent se)方法。
HttpSessionAttributeListener监听HttpSession中的属性的操作。当在Session增加一个属性时，激发attributeAdded(HttpSessionBindingEvent se) 方法；当在Session删除一个属性时，激发attributeRemoved(HttpSessionBindingEvent se)方法；当在Session属性被重新设置时，激发attributeReplaced(HttpSessionBindingEvent se) 方法。

1、通过@ServletComponentScan自动扫描

a、ServletListenerRegistrationBean 注入自定义的Listener；

b、自定义的Listener

@WebListener
public class MyLisener implements ServletContextListener {public void contextInitialized(ServletContextEvent servletContextEvent) {System.out.println("MyLisener contextInitialized method");}public void contextDestroyed(ServletContextEvent servletContextEvent) {System.out.println("MyLisener contextDestroyed method");}
}

2、通过@ServletListenerRegistrationBean 注册

a、@Bean注入自定义的Listener；

@Configuration
public class ServletConfiguration {@Beanpublic ServletListenerRegistrationBean myListener(){return new ServletListenerRegistrationBean(new MyLisener());}
}

b、自定义的Listener

public class MyLisener implements ServletContextListener {public void contextInitialized(ServletContextEvent servletContextEvent) {System.out.println("MyLisener contextInitialized method");}public void contextDestroyed(ServletContextEvent servletContextEvent) {System.out.println("MyLisener contextDestroyed method");}
}

四、验证servlet、filter、listener的顺序

a、使用MyServletDemo2、MyFilter2、MyFilter3、MyLisener做测试；

b、设置servlet处理url格式为 /demo/*；设置MyFilter2顺序为2；MyFilter3的顺序为3；

@Configuration
public class ServletConfiguration {/**代码注入*/@Beanpublic ServletRegistrationBean myServletDemo(){return new ServletRegistrationBean(new MyServletDemo2(),"/demo/*");}@Beanpublic FilterRegistrationBean myFilterDemo(){FilterRegistrationBean registration = new FilterRegistrationBean();registration.setFilter(new MyFilter2());registration.addUrlPatterns("/demo/myFilter");registration.addInitParameter("paramName", "paramValue");registration.setName("myFilter2");registration.setOrder(2);//指定filter的顺序return registration;}@Beanpublic FilterRegistrationBean myFilterDemo2(){FilterRegistrationBean registration = new FilterRegistrationBean();registration.setFilter(new MyFilter3());registration.addUrlPatterns("/demo/*");registration.addInitParameter("paramName", "paramValue");registration.setName("myFilter3");registration.setOrder(1);return registration;}@Beanpublic ServletListenerRegistrationBean myListener(){return new ServletListenerRegistrationBean(new MyLisener());}
}

View Code

c、启动项目后输出：（FIlter2先执行init，因为@Ben在前）

MyLisener contextInitialized method
======MyFilter2 init ……
======MyFilter3 init ……

d、浏览器输入地址地址：http://localhost:8080/demo/myFilter，输出：

======MyFilter3执行过滤操作
======MyFilter2执行过滤操作
>>>>>>>>>>test Get Method==========

可以看出：

Filter3比Filter2先执行；
Filter可以匹配上的url都会执行，并且按顺序执行（Filter的调用链）；
Filter比servlet先执行。
servlet先按具体匹配，然后模糊匹配，并且只能有一个servlet匹配上，没有servlet调用链。

执行顺序是：Listener》Filter》Servlet

五、ApplicationListener自定义侦听器类

参考：http://blog.csdn.net/liaokailin/article/details/48186331

六、Interceptor

拦截器只会处理DispatcherServlet处理的url

a、自定义拦截器

public class MyInterceptor implements HandlerInterceptor {public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {System.out.println(">>>>MyInterceptor preHandle");return true;}public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {System.out.println(">>>>MyInterceptor postHandle");}public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {System.out.println(">>>>MyInterceptor afterCompletion");}
}

b、注册拦截器

@Configuration
public class WebMvcConfiguration extends WebMvcConfigurerAdapter {@Overridepublic void addInterceptors(InterceptorRegistry registry) {registry.addInterceptor(new MyInterceptor()).addPathPatterns("/**");super.addInterceptors(registry);}
}

c、拦截器验证

输入地址：http://localhost:8080/home/test

>>>>MyInterceptor preHandle
>>>>MyInterceptor postHandle
>>>>MyInterceptor afterCompletion

输入地址：http://localhost:8080/demo/myFilter （自定义的Servlet处理了请求，此时拦截器不处理）

拦截器不处理。

转载于:https://www.cnblogs.com/mr-yang-localhost/p/7784607.html