1、定义拦截器
实现 HandlerInterceptor 接口，重写里面重要的三个比较常用的方法
preHandle()：在请求处理之前进行调用（Controller方法调用之前）
postHandle()：请求处理之后进行调用，但是在视图被渲染之前（Controller方法调用之后）
afterCompletion()：在整个请求结束之后被调用，也就是在DispatcherServlet 渲染了对应的视图之后执行（主要是用于进行资源清理工作）

package com.example.demoinitializr.Interceptor;

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

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

public class TestInterceptor implements HandlerInterceptor {
    
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("执行了TestInterceptor的preHandle方法");

        String url = request.getRequestURI();
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String parameter = request.getQueryString();
        String token = request.getHeader("token");

        System.out.println(parameter);

        System.out.println(token);

        if(url=="/user/login"){
            return true;
        }

        if(username == "admin" && password == "123456"){
            return true;
        } else {

        }

        return HandlerInterceptor.super.preHandle(request, response, handler);
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

        System.out.println("执行了TestInterceptor的postHandle方法");

        HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("执行了TestInterceptor的afterCompletion方法");
        
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

2、配置拦截器
继承 WebMvcConfigurer 类，并重写其中的方法 addInterceptors，在主类加上@Configuration在启动的时候在会被加载

package com.example.demoinitializr.config;

import com.example.demoinitializr.Interceptor.TestInterceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebMvcConfig  implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        registry.addInterceptor(TestInterceptor()).addPathPatterns("/**");

        //注册TestInterceptor拦截器
        //InterceptorRegistration registration = registry.addInterceptor(new TestInterceptor());
        //registration.addPathPatterns("/**");                      //所有路径都被拦截
    }

    @Bean
    public TestInterceptor TestInterceptor() {
        return new TestInterceptor();
    }
}

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