SpringBoot注册Filter的两种实现方式

springboot版本：2.2.5

一、filter注册

springboot中添加filter有两种方式：

1、实现方法一

package com.example.demo.filter1;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import org.springframework.stereotype.Component;

/**
 * Springboot实现filter的方式一：
 * 实现Filter接口，并使用@Component注解
 * 需要注意的是：这个方式注册的filter的执行顺序优先级较低
 * @author Administrator
 *
 */
@Component
public class FilterSample1 implements Filter {

  @Override
  public void init(FilterConfig filterConfig) throws ServletException {
    System.out.println("这里是"+this.getClass().getName()+"的init");
    
  }

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    System.out.println("这里是"+this.getClass().getName()+"的doFilter");
    chain.doFilter(request,response);
  }

  @Override
  public void destroy() {
    System.out.println("这里是"+this.getClass().getName()+"的doFilter");
    
  }
}

2、实现方法二

package com.example.demo.filter2;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class FilterSample2 implements Filter{

  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
      throws IOException, ServletException {
    System.out.println("这里是"+this.getClass().getName()+"的doFilter");
    chain.doFilter(request,response);
    
  }
}

package com.example.demo.filter2;

import java.util.ArrayList;

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * Springboot注册filter方法二：
 * 同样要实现filter接口，但filter注册使用@Bean的方式进行注册，可以设置filter顺序
 * @author Administrator
 *
 */
@Configuration
public class WebConfig {
  @Bean
  public FilterRegistrationBean<FilterSample2> filterSample2() {
    FilterRegistrationBean<FilterSample2> registrationBean = new FilterRegistrationBean<FilterSample2>();
    FilterSample2 myFilter = new FilterSample2();
    registrationBean.setFilter(myFilter);
    ArrayList<String> urls = new ArrayList<>();
    urls.add("/*");//配置过滤规则
    registrationBean.setUrlPatterns(urls);
    registrationBean.setOrder(3);
    return registrationBean;
  }
}

二、Springboot自带filter

Springboot默认启用了三个filter，他们是requestContextFilter，characterEncodingFilter，formContentFilter，可以通过在application.yml中设置debug: true来验证如下：

2020-03-17 22:13:17.254 DEBUG 2700 --- [           main] o.s.b.w.s.f.OrderedRequestContextFilter  : Filter 'requestContextFilter' configured for use
2020-03-17 22:13:17.255 DEBUG 2700 --- [           main] s.b.w.s.f.OrderedCharacterEncodingFilter : Filter 'characterEncodingFilter' configured for use
2020-03-17 22:13:17.255 DEBUG 2700 --- [           main] o.s.b.w.s.f.OrderedFormContentFilter     : Filter 'formContentFilter' configured for use

三、查看应用中注册了哪些filter

#application.yml
debug: true

如上图，启用debug模式，查看日志可得：

标蓝部分详细内容如下：

2020-03-17 22:13:17.244 DEBUG 2700 --- [           main] o.s.b.w.s.ServletContextInitializerBeans :
Mapping filters:
filterRegistrationBean urls=[/*] order=3,
characterEncodingFilter urls=[/*] order=-2147483648,
formContentFilter urls=[/*] order=-9900,
requestContextFilter urls=[/*] order=-105,
filterSample1 urls=[/*] order=2147483647

可以看出，该应用注册了五个filter，执行顺序由order决定

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