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(guī)范的所有監(jiān)聽器（如HttpSessionListener監(jiān)聽器）。?

Spring boot 的主 Servlet 為 DispatcherServlet，其默認(rèn)的url-pattern為“/”。一般情況系統(tǒng)默認(rèn)的Servlet就夠用了，如果需要自定義Servlet，可以繼承系統(tǒng)抽象類HttpServlet，重寫方法來實現(xiàn)自己的Servlet。關(guān)于Servlet、過濾器、攔截器、監(jiān)聽器可以參考：（轉(zhuǎn)）servlet、filter、listener、interceptor之間的區(qū)別和聯(lián)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(guī)則：匹配的優(yōu)先級是從精確到模糊，復(fù)合條件的Servlet并不會都執(zhí)行。

1、通過@ServletComponentScan自動掃描

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

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

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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);} }

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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);} }

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二、Filter

完整的流程是：Filter對用戶請求進(jìn)行預(yù)處理，接著將請求交給Servlet進(jìn)行處理并生成響應(yīng)，最后Filter再對服務(wù)器響應(yīng)進(jìn)行后處理。

Filter有如下幾個用處。

• 在HttpServletRequest到達(dá)Servlet之前，攔截客戶的HttpServletRequest。
• 根據(jù)需要檢查HttpServletRequest，也可以修改HttpServletRequest頭和數(shù)據(jù)。
• 在HttpServletResponse到達(dá)客戶端之前，攔截HttpServletResponse。
• 根據(jù)需要檢查HttpServletResponse，也可以修改HttpServletResponse頭和數(shù)據(jù)。

多個FIlter可以組成過濾器調(diào)用鏈，按設(shè)置的順序逐一進(jìn)行處理，形成Filter調(diào)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(zhí)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(xiàn)該方法就可實現(xiàn)對用戶請求進(jìn)行預(yù)處理，也可實現(xiàn)對服務(wù)器響應(yīng)進(jìn)行后處理——它們的分界線為是否調(diào)用了filterChain.doFilter()，執(zhí)行該方法之前，即對用戶請求進(jìn)行預(yù)處理；執(zhí)行該方法之后，即對服務(wù)器響應(yīng)進(jìn)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(zhí)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(jiān)聽對ServletContext屬性的操作，比如增加、刪除、修改屬性。
• ServletContextListener監(jiān)聽ServletContext。當(dāng)創(chuàng)建ServletContext時，激發(fā)contextInitialized(ServletContextEvent sce)方法；當(dāng)銷毀ServletContext時，激發(fā)contextDestroyed(ServletContextEvent sce)方法。
• HttpSessionListener監(jiān)聽HttpSession的操作。當(dāng)創(chuàng)建一個Session時，激發(fā)session Created(HttpSessionEvent se)方法；當(dāng)銷毀一個Session時，激發(fā)sessionDestroyed (HttpSessionEvent se)方法。
• HttpSessionAttributeListener監(jiān)聽HttpSession中的屬性的操作。當(dāng)在Session增加一個屬性時，激發(fā)attributeAdded(HttpSessionBindingEvent se) 方法；當(dāng)在Session刪除一個屬性時，激發(fā)attributeRemoved(HttpSessionBindingEvent se)方法；當(dāng)在Session屬性被重新設(shè)置時，激發(fā)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(shè)置servlet處理url格式為?/demo/*；設(shè)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(zhí)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(zhí)行過濾操作
======MyFilter2執(zhí)行過濾操作
>>>>>>>>>>test Get Method==========

可以看出：

Filter3比Filter2先執(zhí)行；

Filter可以匹配上的url都會執(zhí)行，并且按順序執(zhí)行（Filter的調(diào)用鏈）；

Filter比servlet先執(zhí)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(diào)用鏈。

執(zhí)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");} }

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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

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

輸入地址：http://localhost:8080/demo/myFilter （自定義的Servlet處理了請求，此時攔截器不處理）

攔截器不處理。

轉(zhuǎn)載于:https://www.cnblogs.com/mr-yang-localhost/p/7784607.html

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