doFilter和doFilterInternal OncePerRequestFilter 顾名思义，它能够确保在一次请求中只通过一次filter，而不会重复执行，是由Spring提供的抽象类，重写该接口的dofilterinternal方法，用来记录每次请求ip mac sessionid和返回报文日志

OncePerRequestFilter
顾名思义，它能够确保在一次请求中只通过一次filter，而不会重复执行
是由Spring提供的抽象类
https://www.cnblogs.com/sjxbg/p/13475387.html

摘录自：https://www.jianshu.com/p/3d9b4cfe1a62

doFilter是整个过滤器最底层的概念Filter接口中的方法
所有过滤器都要实现Filter

package javax.servlet;
import java.io.IOException;
public interface Filter {

void init(FilterConfig var1) throws ServletException;
void doFilter(ServletRequest var1, ServletResponse var2, FilterChain var3) throws IOException, ServletException;
void destroy();

}

而doFilterInternal是OncePerRequestFilter 中的一个抽象方法
阅读源码可知：
OncePerRequestFilter.doFilter方法中通过request.getAttribute判断当前过滤器是否已执行
若未执行过，则调用doFilterInternal方法，交由其子类实现

OncePerRequestFilter
顾名思义，它能够确保在一次请求中只通过一次filter，而不会重复执行
是由Spring提供的抽象类

package org.springframework.session.web.http;
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 javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;
abstract class OncePerRequestFilter implements Filter {

public static final String ALREADY_FILTERED_SUFFIX = ".FILTERED";

private String alreadyFilteredAttributeName = this.getClass().getName().concat(".FILTERED");
OncePerRequestFilter() {

}
public final void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws ServletException, IOException {

if (request instanceof HttpServletRequest && response instanceof HttpServletResponse) {

HttpServletRequest httpRequest = (HttpServletRequest)request;

HttpServletResponse httpResponse = (HttpServletResponse)response;

boolean hasAlreadyFilteredAttribute = request.getAttribute(this.alreadyFilteredAttributeName) != null;

if (hasAlreadyFilteredAttribute) {

filterChain.doFilter(request, response);

} else {

request.setAttribute(this.alreadyFilteredAttributeName, Boolean.TRUE);
try {

this.doFilterInternal(httpRequest, httpResponse, filterChain);

} finally {

request.removeAttribute(this.alreadyFilteredAttributeName);

}

}
} else {

throw new ServletException("OncePerRequestFilter just supports HTTP requests");

}

}
protected abstract void doFilterInternal(HttpServletRequest var1, HttpServletResponse var2, FilterChain var3) throws ServletException, IOException;
public void init(FilterConfig config) {

}
public void destroy() {

}

}

常识上都认为，一次请求本来就只filter一次，为什么还要由此特别限定呢？
往往我们的常识和实际的实现并不真的一样，经过一番资料的查阅，此方法是为了兼容不同的web container
也就是说并不是所有的container都入我们期望的只过滤一次，servlet版本不同，执行过程也不同
因此，为了兼容各种不同运行环境和版本，默认filter继承OncePerRequestFilter是一个比较稳妥的选择。