第二章 SpringBoot整合过滤器、监听器

一 整合过滤器

在SpringBoot项目中要实现自己的过滤器很简单 只需要如下几步即可

• 集成starter-web依赖

   <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
  

• 实现Filter接口

    //@Order(1) @Order注解并不能控制filter的执行顺序 它只能决定spring容器装载bean的一个顺序 如果你需要对filter的执行顺序
    //做控制 建议使用 FilterRegistration
    @WebFilter(filterName = "MyFilter", urlPatterns = "/*")
    public class MyFilter implements Filter {
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            System.out.println("过滤器初始化");
            Filter.super.init(filterConfig);
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            System.out.println("进行过滤处理");
            chain.doFilter(request, response);
        }
    
        @Override
        public void destroy() {
            Filter.super.destroy();
            System.out.println("销毁过滤器");
        }
    }
  

• 在启动类上添加@ServletComponentScan注解

    //@ServletComponentScan 默认会扫描当前类(启动类)所在包及其子包下的所有的servlet相关注解
    @ServletComponentScan
    @SpringBootApplication
    public class SpringbootDemo1Application {
    
        public static void main(String[] args) {
            SpringApplication.run(SpringbootDemo1Application.class, args);
        }
    
    }
  

• 使用FilterRegistrationBean注册filter
  如果基于注解方式不够灵活 也可以通过ServletRegistrationBean、FilterRegistrationBean、以及ServletListenerRegistrationBean类来将Servlet、Filter和Listener来注册为spring的bean 同样也可以达到上面的效果。这里演示如何利用FilterRegistration类来实现filter

    //过滤器一 不需要加任何的注解
    public class MyFilter implements Filter {
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            System.out.println("过滤器初始化1");
            Filter.super.init(filterConfig);
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            System.out.println("进行过滤处理1");
            chain.doFilter(request, response);
        }
    
        @Override
        public void destroy() {
            Filter.super.destroy();
            System.out.println("销毁过滤器1");
        }
    }
    
    //过滤器二 不需要加任何的注解
    public class MyFilter2 implements Filter {
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            Filter.super.init(filterConfig);
            System.out.println("过滤器初始化2");
        }
    
        @Override
        public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
            System.out.println("进行过滤处理2");
            chain.doFilter(request, response);
        }
    
        @Override
        public void destroy() {
            Filter.super.destroy();
            System.out.println("销毁过滤器2");
        }
    }
    
    //启动类也不需要加@ServletComponentScan注解进行扫描
    @SpringBootApplication
    public class SpringbootDemo1Application {
    
        public static void main(String[] args) {
            SpringApplication.run(SpringbootDemo1Application.class, args);
        }
    
    }
    
    //新增一个配置类
    @Configuration
    public class FilterConfig {
            
        //利用FilterRegistrationBean将filter装配为一个bean 并且通过setOrder方法去控制filter的执行顺序
        @Bean
        public FilterRegistrationBean filterRegistration() {
            FilterRegistrationBean<MyFilter> registration = new FilterRegistrationBean<>();
            registration.setFilter(new MyFilter());
            registration.addUrlPatterns("/*");
            registration.setOrder(1); //过滤器的执行顺序
            registration.setName("MyFilter");
            return registration;
        }
    
        @Bean
        public FilterRegistrationBean filterRegistration2() {
            FilterRegistrationBean<MyFilter2> registration = new FilterRegistrationBean<>();
            registration.setFilter(new MyFilter2());
            registration.addUrlPatterns("/*");
            registration.setOrder(2); //过滤器的执行顺序
            registration.setName("MyFilter2");
            return registration;
        }
    }
  

二 集成监听器

listener是servlet规范定义的一种特殊类，用于监听servletContext、HttpSession和servletRequest等域对象的创建和销毁事件。监听域对象的属性发生修改的事件，用于在事件发生前、发生后做一些必要的处理。可用于以下方面1、统计在线人数和在线用户 2、系统启动时加载初始化信息3、统计网站访问量4、记录用户访问路径

• 利用@WebListener注解创建监听器

    //监听器需要自己去实现相应的listener接口 @WebListener注解 需要与@ServletComponentScan注解配合使用
    //listener才会生效
    @WebListener
    public class MySessionListener implements HttpSessionListener {
        @Override
        public void sessionCreated(HttpSessionEvent se) {
            System.out.println("创建session");
        }
    
        @Override
        public void sessionDestroyed(HttpSessionEvent se) {
            System.out.println("销毁session");
        }
    }
    
    //启动类 加上@ServletComponentScan注解
    @ServletComponentScan
    @SpringBootApplication
    public class SpringbootDemo1Application {
    
        public static void main(String[] args) {
            SpringApplication.run(SpringbootDemo1Application.class, args);
        }
    
    }
    
    //测试类 需要通过request.getSession()触发HttpSessionListener监听的事件
    @RestController
    public class TestController {
    
        @RequestMapping(path = "/hello", method = RequestMethod.GET)
        public String hello(HttpServletRequest request) {
            request.getSession(); //触发session的创建
            return "hello";
        }
    }
  

• 利用ServletListenerRegistrationBean创建listener
  ServletListenerRegistrationBean创建listener 可以对listener进行一些细粒度的控制 如listener的执行顺序等

    //不需要加任何的注解 启动类上也不需要加@ServletComponentScan注解
    public class MySessionListener implements HttpSessionListener {
        @Override
        public void sessionCreated(HttpSessionEvent se) {
            System.out.println("创建session");
        }
    
        @Override
        public void sessionDestroyed(HttpSessionEvent se) {
            System.out.println("销毁session");
        }
    }
    
    @Configuration
    public class ListenerConfig {
        
        //通过ServletListenerRegistrationBean的方式将listener注入到spring容器中
        @Bean
        public ServletListenerRegistrationBean<MySessionListener> listenerRegistrationBean() {
            ServletListenerRegistrationBean<MySessionListener> registrationBean = new ServletListenerRegistrationBean<>();
            registrationBean.setListener(new MySessionListener());
            registrationBean.setOrder(1); //设置监听器的执行顺序
            return registrationBean;
        }
    }
    
    //测试类
    @RestController
    public class TestController {
    
        @RequestMapping(path = "/hello", method = RequestMethod.GET)
        public String hello(HttpServletRequest request) {
            request.getSession(); //触发session的创建
            return "hello";
        }
    }
    
    //启动类
    @SpringBootApplication
    public class SpringbootDemo1Application {
    
        public static void main(String[] args) {
            SpringApplication.run(SpringbootDemo1Application.class, args);
        }
    
    }
  

三 静态资源的配置

默认情况下，SpringBoot将在classpath或者ServletContext根目录下从名为/static(/pulic、/resources、或/META-INF/resources)目录中加载静态资源。它使用了SpringMVC的ResourceHttpRequestHandler，因此也可以通过实现WebMvcConfigurer接口重写addResourceHandlers方法来自己自定义springboot中的静态资源目录
示例

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        //过滤swagger 如果访问的uri是swagger-ui.html 将会映射到classpath:/META-INF/resources/这个目录下去找对应的静态资源
        registry.addResourceHandler("swagger-ui.html")
                .addResourceLocations("classpath:/META-INF/resources/");

        registry.addResourceHandler("/webjars/**")
                .addResourceLocations("classpath:/META-INF/resources/webjars/");

        registry.addResourceHandler("/swagger-resources/**")
                .addResourceLocations("classpath:/META-INF/resources/swagger-resources/");

        registry.addResourceHandler("/swagger/**")
                .addResourceLocations("classpath:/META-INF/resources/swagger*");

        registry.addResourceHandler("/v2/api-docs/**")
                .addResourceLocations("classpath:/META-INF/resources/v2/api-docs/");
    }
}