在SpringBoot中使用Filter过滤器

前言

本文记录一下在 SpringBoot 项目中是如何使用 Filter 过滤器

代码、测试

Filter 过滤器是 servlet 包下面的东西，因此我们不需要再额外引包

方法一

直接实现 Filter 接口，并使用 @Component 注解标注为组件自动注入 bean

package cn.huanzi.qch.springbootfilter.filter;
import org.springframework.stereotype.Component;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@Component
public class TestFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        System.out.println("TestFilter,"+request.getRequestURI());
        //执行
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void destroy() {
    }
}

查看日志可以发现，SpringBoot 已经帮我们注入了一个 filter，拦截路径是 /*，拦截所有，如果我们需要进一步拦截具体的则需要我们自己在代码里控制

方法二

实现 Filter 接口，用 @WebFilter 注解，指定拦截路径以及一些参数，同时需要在启动类使用 @ServletComponentScan 扫描带 @WebFilter、@WebServlet、@WebListener 并将帮我们注入 bean

请看官网介绍：https://docs.spring.io/spring-boot/docs/2.1.5.RELEASE/reference/htmlsingle/#boot-features-embedded-container-servlets-filters-listeners-scanning

package cn.huanzi.qch.springbootfilter.filter;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
//配置拦截路径
@WebFilter(filterName = "testFilter",urlPatterns = {"/test"})
public class TestFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        System.out.println("TestFilter,"+request.getRequestURI());
        //执行
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void destroy() {
    }
}

package cn.huanzi.qch.springbootfilter;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
//自动扫描与当前类的同包以及子包
@ServletComponentScan
@SpringBootApplication
public class SpringbootFilterApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootFilterApplication.class, args);
    }
}

查看日志发现，以及帮我们注入了 testFilter，拦截路径是 / test

只指定拦截路径，不设置 filterName 一样可以注入

//配置拦截路径
@WebFilter({"/test"})

方法三

当然了，我们也可以既使用 @Component 同时也使用 @WebFilter

package cn.huanzi.qch.springbootfilter.filter;
import org.springframework.stereotype.Component;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
//配置拦截路径
@WebFilter(filterName = "testFilter",urlPatterns = {"/test"})
@Component
public class TestFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        System.out.println("TestFilter,"+request.getRequestURI());
        //执行
        filterChain.doFilter(servletRequest, servletResponse);
    }
    @Override
    public void destroy() {
    }
}

package cn.huanzi.qch.springbootfilter;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
//自动扫描与当前类的同包以及子包
@ServletComponentScan
@SpringBootApplication
public class SpringbootFilterApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootFilterApplication.class, args);
    }
}

但是做会注入两个 bean，如果你的 @WebFilter 没有指定 filterName 或者指定的名称与类名相同，由于注入两个相同名称的 bean，程序启动报错，叫我们修改其中一个的名字，或者启用覆盖 bean

这里建议如果你硬要采用第三种方法，最好启用覆盖，因为改名将会注入两个 bean，处理逻辑一样但拦截路径不一样，这并不是我们想要的，例如：

启用覆盖

#启用覆盖同名bean
spring.main.allow-bean-definition-overriding=true

PS：这里额外说一点，如果我们采用第三种方法，@ServletComponentScan 放在 TestFilter 类上 @WebFilter 也会被扫描到，不需要放在启动类，第二种方法如果也这样做就不行，估计是受到了 @Component 注解的影响

//配置拦截路径
@WebFilter(filterName = "testFilter",urlPatterns = {"/test"})
@ServletComponentScan
@Component
public class TestFilter implements Filter