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SpringBoot从入门到精通-第6章 过滤器

Filter过滤器是单独的类文件，不写在控制层、服务层、持久层。
写好正确的注解和扫描，程序启动时就会第一时间到过滤器。
过滤器注解：
@WebFilter(“/*”)用于类上，过滤url
@Component和@WebFilter注解一起使用，让主程序能扫描到过滤器
前提是过滤器类实现Filter接口。

一、过滤器简介

二、通过注解配置过滤器

2.1先启动一个简单的Springboot程序
pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>3.5.0</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.example</groupId><artifactId>_20250611spring_Filter</artifactId><version>0.0.1-SNAPSHOT</version><name>20250611spring_Filter</name><description>20250611spring_Filter</description><url/><licenses><license/></licenses><developers><developer/></developers><scm><connection/><developerConnection/><tag/><url/></scm><properties><java.version>17</java.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>

2.2编写控制器类

package com.example._20250611spring_filter.controller;import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;@RestController
@ResponseBody
public class FilterController {@RequestMapping("/filter")public String soutFilter(){System.out.println("this is filter");return "This is Filter!";}
}

2.3启动项目后浏览器访问http://127.0.0.1:8080/filter

2.4配置过滤器类

package com.example._20250611spring_filter.filter;import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import org.springframework.stereotype.Component;import java.io.FileFilter;
import java.io.IOException;
@WebFilter("/*")
@Component
public class TestFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("before doFilter() !!!");filterChain.doFilter(servletRequest,servletResponse);System.out.println("after doFilter() !!!");}
}

2.5过滤器内容释义：

• import java.io.FileFilter;注意实现Filter接口时候需要选择与springboot适配的包。
• @WebFilter(“/*”)注解标注要过滤的路径，这里过滤所有
• @Component注解让主程序启动时扫描到过滤器类
• public void doFilter()过滤方法，是Filter接口的方法，必须要实现
• filterChain.doFilter(servletRequest,servletResponse)方法是过滤方法过滤结束后放行，即过滤器过滤完去程序执行任务。是固定写法。
• Filetr接口有3个方法，初始化方法和销毁方法可以不用必须被重写。
• 

2.6测试访问http://127.0.0.1:8080/filter
如果没有filterChain.doFilter(servletRequest,servletResponse);放行，“this is filter”和“after doFilter() !!!”是不会被打印的。

三、实例
用过滤器统计资源访问量
3.1配置过滤器类

package com.example._20250611spring_filter.filter;import jakarta.servlet.*;
import jakarta.servlet.annotation.WebFilter;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import org.springframework.stereotype.Component;import java.io.FileFilter;
import java.io.IOException;
@WebFilter("/filter")
@Component
public class TestFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {ServletContext context = filterConfig.getServletContext();context.setAttribute("count",0);}@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("before doFilter() !!!");HttpServletRequest req = (HttpServletRequest) servletRequest;ServletContext context = req.getServletContext();Integer count = (Integer) context.getAttribute("count");context.setAttribute("count",++count);filterChain.doFilter(servletRequest,servletResponse);System.out.println("after doFilter() !!!");}
}

3.2配置控制器类

package com.example._20250611spring_filter.controller;import jakarta.servlet.ServletContext;
import jakarta.servlet.http.HttpServletRequest;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;@RestController
@ResponseBody
public class FilterController {@RequestMapping("/filter")public String soutFilter(HttpServletRequest request){ServletContext context = request.getServletContext();Integer count = (Integer) context.getAttribute("count");return "当前访问量："+count;
//        System.out.println("this is filter");
//        return "This is Filter!";}
}

3.3访问测试

四、通过FilterRegistrationBean类配置过滤器