【SpringBoot中实现过滤器和拦截器】

1 过滤器Filter和拦截器Interceptor，在功能方面很类似，但在具体实现方面差距还是比较大的。

2.过滤器的配置

2.1 自定义过滤器，实现Filter接口(SpringBoot 3开始，jakarta.servlet.Filter)

2.2 重写doFilter，实现过滤逻辑，酌情放行

package com.lenovo.springboot.filter;

import io.swagger.v3.oas.models.security.SecurityScheme;
import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;

import java.io.IOException;
import java.util.Objects;

@WebFilter(urlPatterns = "/*")
public class MyFilter implements Filter {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;
        HttpServletResponse httpResponse = (HttpServletResponse) servletResponse;
        String ip = httpRequest.getRemoteAddr();

        HttpSession session = httpRequest.getSession();

        Integer count =  (Integer) session.getAttribute("count");

        count = Objects.isNull(count) ? 1: ++count;
        System.out.println("ip"+ip+"\tcount"+count);

        session.setAttribute("count",count);
        filterChain.doFilter(servletRequest,servletResponse);

    }
}

2.3 创建注解，实现过滤的范围配置

启动文件中加入 

@ServletComponentScan(basePackages = "com.lenovo.springboot.filter")

3.拦截器的配置
3.1 白定义拦截器，实现HandlerInterceptor接口
3.2 实现接口中的拦截方法(preHandle-请求执行前、postHandler-请求执行后、afterCompletion-视图渲染后)

package com.lenovo.springboot.interceptor;

import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;
import org.springframework.web.servlet.HandlerInterceptor;

import java.util.Objects;

public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {

        String ip = request.getRemoteAddr();

        HttpSession session = request.getSession();

        Integer count =  (Integer) session.getAttribute("countip");

        count = Objects.isNull(count) ? 1: ++count;
        System.out.println("ip##"+ip+"\tcountip##"+count);

        session.setAttribute("countip",count);
        //放行
        return true;
    }
}

3.3 创建配置类，实现WebMvcconfigurer接口，重写addInterceptors方法

package com.lenovo.springboot.config;

import com.lenovo.springboot.interceptor.MyInterceptor;
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 InterceptorConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {

        MyInterceptor myInterceptor = new MyInterceptor();
        registry.addInterceptor(myInterceptor).addPathPatterns("/**");
    }
}

4.总结
4.1 Filter依赖于servlet容器，属于Servlet规范的一部分，而Interceptor依赖于SpringMVC框架:
4.2 Filter的生命周期由servlet容器管理，而Interceptor通过IOC容器来管理，可通过注入等方式来获取其Bean
4.3 Filter可拦截所有web资源(包括Jsp，Servlet，静态资源)，而Interceptor则只拦截controller。