Java的Servlet、Filter、Interceptor、Listener

寫在前面：

使用Spring-Boot時，嵌入式Servlet容器可以通過掃描注解（@ServletComponentScan）的方式注冊Servlet、Filter和Servlet規范的所有監聽器（如HttpSessionListener監聽器）。?

Spring boot 的主 Servlet 為 DispatcherServlet，其默認的url-pattern為“/”。一般情況系統默認的Servlet就夠用了，如果需要自定義Servlet，可以繼承系統抽象類HttpServlet，重寫方法來實現自己的Servlet。關于Servlet、過濾器、攔截器、監聽器可以參考：（轉）servlet、filter、listener、interceptor之間的區別和聯系

Spring-Boot有兩種方法注冊Servlet、Filter和Listener?：

1、代碼注冊：通過ServletRegistrationBean、 FilterRegistrationBean 和 ServletListenerRegistrationBean 獲得控制。

2、在 SpringBootApplication 上使用@ServletComponentScan 注解后，Servlet、Filter、Listener 可以直接通過 @WebServlet、@WebFilter、@WebListener 注解自動注冊，無需其他代碼。

一、Servlet

Servlet匹配規則：匹配的優先級是從精確到模糊，復合條件的Servlet并不會都執行。

1、通過@ServletComponentScan自動掃描

a、springboot的啟動入口添加注解：@ServletComponentScan；

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

b、@WebServlet 自定義Servlet，配置處理請求路徑?/demo/myServlet?

@WebServlet(name = "myServletDemo1",urlPatterns = "/demo/myServlet",description = "自定義的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注入自定義的Servlet，配置處理的路徑為?/demo/servletDemo2?

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

b、自定義的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對用戶請求進行預處理，接著將請求交給Servlet進行處理并生成響應，最后Filter再對服務器響應進行后處理。

Filter有如下幾個用處。

在HttpServletRequest到達Servlet之前，攔截客戶的HttpServletRequest。
根據需要檢查HttpServletRequest，也可以修改HttpServletRequest頭和數據。
在HttpServletResponse到達客戶端之前，攔截HttpServletResponse。
根據需要檢查HttpServletResponse，也可以修改HttpServletResponse頭和數據。

多個FIlter可以組成過濾器調用鏈，按設置的順序逐一進行處理，形成Filter調用鏈。

1、通過@ServletComponentScan自動掃描

a、springboot的啟動入口添加注解：@ServletComponentScan；

b、@WebFilter 配置處理全部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(">>>>>>執行過濾操作");filterChain.doFilter(servletRequest, servletResponse);}public void destroy() {System.out.println(">>>>>>myFilter destroy ……");}
}

?*?doFilter()方法是過濾器的核心方法，實現該方法就可實現對用戶請求進行預處理，也可實現對服務器響應進行后處理——它們的分界線為是否調用了filterChain.doFilter()，執行該方法之前，即對用戶請求進行預處理；執行該方法之后，即對服務器響應進行后處理。

2、通過@FilterRegistrationBean注冊

a、@Bean注入自定義的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的順序return registration;}
}

b、自定義的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執行過濾操作");filterChain.doFilter(servletRequest, servletResponse);}public void destroy() {System.out.println("======MyFilter2 destroy ……");}
}

三、Listener

目前 Servlet 中提供了 6 種兩類事件的觀察者接口，它們分別是：4 個 EventListeners 類型的，ServletContextAttributeListener、ServletRequestAttributeListener、ServletRequestListener、HttpSessionAttributeListener 和 2 個 LifecycleListeners 類型的，ServletContextListener、HttpSessionListener。

ServletContextAttributeListener監聽對ServletContext屬性的操作，比如增加、刪除、修改屬性。
ServletContextListener監聽ServletContext。當創建ServletContext時，激發contextInitialized(ServletContextEvent sce)方法；當銷毀ServletContext時，激發contextDestroyed(ServletContextEvent sce)方法。
HttpSessionListener監聽HttpSession的操作。當創建一個Session時，激發session Created(HttpSessionEvent se)方法；當銷毀一個Session時，激發sessionDestroyed (HttpSessionEvent se)方法。
HttpSessionAttributeListener監聽HttpSession中的屬性的操作。當在Session增加一個屬性時，激發attributeAdded(HttpSessionBindingEvent se) 方法；當在Session刪除一個屬性時，激發attributeRemoved(HttpSessionBindingEvent se)方法；當在Session屬性被重新設置時，激發attributeReplaced(HttpSessionBindingEvent se) 方法。

1、通過@ServletComponentScan自動掃描

a、ServletListenerRegistrationBean?注入自定義的Listener；

b、自定義的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、通過@ServletListenerRegistrationBean?注冊

a、@Bean注入自定義的Listener；

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

b、自定義的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、驗證servlet、filter、listener的順序

a、使用MyServletDemo2、MyFilter2、MyFilter3、MyLisener做測試；

b、設置servlet處理url格式為?/demo/*；設置MyFilter2順序為2；MyFilter3的順序為3；

@Configuration
public class ServletConfiguration {/**代碼注入*/@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的順序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、啟動項目后輸出：（FIlter2先執行init，因為@Ben在前）

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

d、瀏覽器輸入地址地址：http://localhost:8080/demo/myFilter，輸出：

======MyFilter3執行過濾操作
======MyFilter2執行過濾操作
>>>>>>>>>>test Get Method==========

可以看出：

Filter3比Filter2先執行；
Filter可以匹配上的url都會執行，并且按順序執行（Filter的調用鏈）；
Filter比servlet先執行。
servlet先按具體匹配，然后模糊匹配，并且只能有一個servlet匹配上，沒有servlet調用鏈。

執行順序是：Listener》Filter》Servlet

五、ApplicationListener自定義偵聽器類

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

六、Interceptor

攔截器只會處理DispatcherServlet處理的url

a、自定義攔截器

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、注冊攔截器

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

c、攔截器驗證

輸入地址：http://localhost:8080/home/test