从零学springboot—— servlet,过滤器，监听器，拦截器

拼搏现实的明天。 2022-05-24 11:04 212阅读 0赞

## 自定义servlet ##

@WebServlet(urlPatterns = "/myServlet/*")
    public class MyServlet extends HttpServlet { 
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
            System.out.println("********get请求***********");
        }
    
        protected void doPost(HttpServletRequest req, HttpServletResponse resp){
            System.out.println("********post请求***********");
        }
    }

在启动类上添加注解@ServletComponentScan，过滤器和监听器也需要开启该注解。

## 过滤器实现 ##

@WebFilter(urlPatterns="/*")
    public class MyFilter implements Filter { 
    
        @Override
        public void init(FilterConfig filterConfig) throws ServletException {
            System.err.println("********过滤器初始化*********");
        }
    
        @Override
        public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
            System.err.println("********过滤器执行*********");
            filterChain.doFilter(servletRequest,servletResponse);
        }
    
        @Override
        public void destroy() {
            System.err.println("********过滤器销毁*********");
        }
    }

## 监听器实现 ##

@WebListener
    public class MyServletContextListen implements ServletContextListener { 
    
        @Override
        public void contextInitialized(ServletContextEvent servletContextEvent) {
            System.err.println("***********容器启动**************");
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent servletContextEvent) {
            System.err.println("***********容器销毁**************");
        }
    }

其中示例中的监听器为监听容器的启动及销毁，还存在其他的监听器接口，例如监听session的HttpSessionListener（多用于统计在线人数），监听ServletRequest对象的ServletRequestListener

## 拦截器实现 ##

自定义拦截器：

public class MyInterceptor1 implements HandlerInterceptor { 
    
        @Override
        public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
            System.err.println("*********拦截器1执行*********");
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
    
        }
    
        @Override
        public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
    
        }
    }

public class MyInterceptor2 implements HandlerInterceptor { 
    
        @Override
        public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o) throws Exception {
            System.err.println("***********拦截器2执行**************");
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
    
        }
    
        @Override
        public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {
    
        }
    }

将自定义拦截器加入到拦截器链：

@Configuration
    public class MyWebAppConfigurer extends WebMvcConfigurerAdapter { 
    
        @Override
        public void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new MyInterceptor1());
            registry.addInterceptor(new MyInterceptor2());
            super.addInterceptors(registry);
        }
    }

这里过滤器，监听器，拦截器有个请求顺序，例如对于同一个请求，会先执行监听该请求的监听器，然后执行过滤器，再执行拦截器。