Spring Boot 知识笔记（servlet、监听器、拦截器）

一、通过注解自定义servlet

package net.Eleven.demo.servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet(name = "userServlet",urlPatterns = "/servlet/test/customs")
public class UserServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().print("custom sevlet");
        resp.getWriter().flush();
        resp.getWriter().close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

返回结果

二、通过注解自定义ServletRequestListener

package net.Eleven.demo.Listener;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class RequestListener implements ServletRequestListener {
    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println("==========RequestDestroyed========");
    }

    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("==========RequestInitialized=======");

    }
}

返回结果

三、通过注解自定义ServletContextListener

package net.Eleven.demo.Listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

@WebListener
public class CustomContextListener   implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("=======contextInitialized========");
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("=======contextDestroyed========");

    }
}

四、拦截器

1、先定义拦截配置器

package net.Eleven.demo.Intecpter;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class CustomWebMvcConfigurer  implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginIntercepter()).addPathPatterns("/success/*");  //注册一个拦截器
        WebMvcConfigurer.super.addInterceptors(registry);
    }
}

2、根据业务需要定义拦截器

package net.Eleven.demo.Intecpter;

import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginIntercepter  implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("LoginIntercepter========>preHandle");
        return HandlerInterceptor.super.preHandle(request,response,handler);
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("LoginIntercepter========>postHandle");
         HandlerInterceptor.super.postHandle(request,response,handler,modelAndView);

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("LoginIntercepter========>afterCompletion");
         HandlerInterceptor.super.afterCompletion(request,response,handler,ex);
    }
}

返回结果：

拦截器不生效常见问题：
1）是否有加@Configuration
2）拦截路径是否有问题 ** 和 *
3）拦截器最后路径一定要 “/**”， 如果是目录的话则是 /*/

Filter是基于函数回调 doFilter()，而Interceptor则是基于AOP思想
Filter在只在Servlet前后起作用，而Interceptor够深入到方法前后、异常抛出前后等

Filter依赖于Servlet容器即web应用中，而Interceptor不依赖于Servlet容器所以可以运行在多种环境。

在接口调用的生命周期里，Interceptor可以被多次调用，而Filter只能在容器初始化时调用一次。

Filter和Interceptor的执行顺序

过滤前->拦截前->action执行->拦截后->过滤