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 {
    @Override
    protected 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);
    }

    @Override
    protected 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
     */
    @Bean
    public ServletRegistrationBean myServletDemo() {
        return new ServletRegistrationBean(new MyServletDemo2(), "/demo/servletDemo2");
    }
}

b、自定义的Servlet

public class MyServletDemo2 extends HttpServlet {
    @Override
    protected 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);
    }

    @Override
    protected 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 {
    @Bean
    public 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 {
    @Bean
    public 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*/
    @Bean
    public ServletRegistrationBean myServletDemo(){
        return new ServletRegistrationBean(new MyServletDemo2(),"/demo/*");
    }

    @Bean
    public 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;
    }

    @Bean
    public 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;
    }

    @Bean
    public 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:

  1. Filter3比Filter2先执行;
  2. Filter可以匹配上的url都会执行,并且按顺序执行(Filter的调用链);
  3. Filter比servlet先执行。
  4. 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 {
    @Override
    public 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。

posted @ 2017-11-09 23:31  Mr.yang.localhost  阅读(3214)  评论(0编辑  收藏  举报