拦截器源码分析

@Slf4j
@Controller
public class BlueController {


    @ResponseBody
    @GetMapping("/bb")
    public String bb(HttpSession session){
        return session.getAttribute("name").toString();
    }

    @ResponseBody
    @GetMapping("/login")
    public String login(HttpSession session){
        log.info("登陆进来了");
        session.setAttribute("name","123");
        return "success";
    }

}

package com.example.client.config;

import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

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

@Slf4j
//登陆拦截器
public class LoginInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //请求操作之前
        log.info("请求操作之前");
        Object name = request.getSession().getAttribute("name");
        if(name!=null){
            //如果不为空 放行
            return true;
        }
        //跳转到登陆界面
        response.sendRedirect("/login");
        //如果为空 拦截住
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("请求操作之后");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("视图渲染之后");
    }
}

package com.example.client.config;

import com.baomidou.mybatisplus.core.toolkit.StringUtils;
import com.example.client.entity.Actor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.ParameterizedTypeReference;
import org.springframework.core.convert.converter.Converter;
import org.springframework.format.FormatterRegistry;
import org.springframework.http.MediaType;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.web.accept.HeaderContentNegotiationStrategy;
import org.springframework.web.accept.ParameterContentNegotiationStrategy;
import org.springframework.web.filter.HiddenHttpMethodFilter;
import org.springframework.web.servlet.config.annotation.ContentNegotiationConfigurer;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

import java.util.*;


@Configuration
public class TestConfig implements WebMvcConfigurer{


    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //注册拦截器
        registry.addInterceptor(new LoginInterceptor())
                //拦截所有请求
                .addPathPatterns("/**")
                //放行资源
                .excludePathPatterns("/","/login");
    }
}

http://localhost:8080/bb

第一次跳转到登陆界面 拦截住了

第二次在访问bb,就是显示内容了

我们来看下源码，进入DispatcherServlet类

在这里获取handler

根据当前请求，找到可以处理请求的handler以及handler的所有拦截器

会显示我们自定义的登陆拦截器

走到applyPreHandle 点进去

在这里会遍历所有的拦截器

然后走到interceptor.preHandle这里的时候，会进入我们的登陆拦截器

当返回false的时候会进入triggerAfterCompletion方法，倒叙

如果interceptorIndex 拦截器索引大于-1，那么就会进入这个循环

获取对应的拦截器进入afterCompletion方法