过滤器（Filter）的实现方式

Filter是单例的。实现过滤器(Filter)首先需要实现Filter类。
具体实现方式有3种：

1. 实现Filter类，使用@Component注解注册到Spring
2. 实现Filter类，使用@Configuration注解，用配置bean的方式装配
3. 实现Filter类，使用@WebFilter注解

1.实现Filter类，使用@Component注解注册到Spring

package com.example.filter;

import org.springframework.stereotype.Component;

import javax.servlet.*;
import java.io.IOException;
import java.util.Date;


@Component
public class MyFilter implements Filter {

	//创建之后，马上执行；Filter会在服务器启动时就创建！
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("MyFilter.init");
    }


     
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("MyFilter start");
        Long startTime = new Date().getTime();
        chain.doFilter(request, response);
        System.out.println("MyFilter 耗时：" + (new Date().getTime() - startTime));
        System.out.println("MyFilter end");
    }

	 //销毁之前执行！在服务器关闭时销毁
    @Override
    public void destroy() {
        System.out.println("MyFilter.destroy>>>>>>>>>");
    }
}

2.实现Filter类，使用@Configuration注解，用配置bean的方式装配
以上代码不变，但是MyFilter类需要去掉@Component。然后再自定义一个配置类

package com.example.filter;

import javax.servlet.*;
import java.io.IOException;
import java.util.Date;

public class MyFilter implements Filter {

	//创建之后，马上执行；Filter会在服务器启动时就创建！
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("MyFilter.init");
    }

     
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("MyFilter start");
        Long startTime = new Date().getTime();
        chain.doFilter(request, response);
        System.out.println("MyFilter 耗时：" + (new Date().getTime() - startTime));
        System.out.println("MyFilter end");
    }

	 //销毁之前执行！在服务器关闭时销毁
    @Override
    public void destroy() {
        System.out.println("MyFilter.destroy>>>>>>>>>");
    }
}

package com.example.filter;

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

@Configuration
public class MyConfig {
    @Bean
    public FilterRegistrationBean registrationBean(){
        FilterRegistrationBean registrationBean = new FilterRegistrationBean();
        registrationBean.setFilter(new MyFilter());
        registrationBean.addUrlPatterns("
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("MyFilter start");
        Long startTime = new Date().getTime();
        chain.doFilter(request, response);
        System.out.println("MyFilter 耗时：" + (new Date().getTime() - startTime));
        System.out.println("MyFilter end");
    }

    //销毁之前执行！在服务器关闭时销毁
    @Override
    public void destroy() {
        System.out.println("MyFilter.destroy>>>>>>>>>");
    }
}