JAVA-springboot Filter过滤器

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 {
    @Override
    public 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 {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        ServletContext context = filterConfig.getServletContext();
        context.setAttribute("count",0);
    }

    @Override
    public 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