我正试着了解SpringSecurity，阅读SpringSecurity教程，我在下面遇到了这段代码。在 doFilterInternal 方法检查是否设置了授权令牌，如果未设置，则直接调用 filterChain.doFilter() 方法。如果设置了授权令牌，只需显式地将授权令牌添加到安全上下文中，然后调用 filterChain.doFilter() . 这有什么必要？为什么要将authenticationtoken设置为 SecurityContext 明确地？
代码

package com.betterjavacode.SpringAppCache;

import io.jsonwebtoken.Jwts;

import org.springframework.security.authentication.AuthenticationManager;

import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;

import org.springframework.security.core.context.SecurityContextHolder;

import org.springframework.security.web.authentication.www.BasicAuthenticationFilter;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.IOException;

import java.util.ArrayList;

public class AuthorizationFilter extends BasicAuthenticationFilter

{

    public AuthorizationFilter(AuthenticationManager authenticationManager)
    {

        super(authenticationManager);

    }

    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)

            throws IOException, ServletException

    {

        String header = request.getHeader("Authorization");

        if(header == null || !header.startsWith("Bearer"))

        {

            filterChain.doFilter(request,response);

            return;

        }

        UsernamePasswordAuthenticationToken authenticationToken = getAuthentication(request);

        SecurityContextHolder.getContext().setAuthentication(authenticationToken);

        filterChain.doFilter(request,response);

    }

    private UsernamePasswordAuthenticationToken getAuthentication(HttpServletRequest request)

    {

        String token = request.getHeader("Authorization");

        if(token != null)

        {

            String user = Jwts.parser().setSigningKey("SecretKeyToGenJWTs".getBytes())

                    .parseClaimsJws(token.replace("Bearer",""))

                    .getBody()

                    .getSubject();

            if(user != null)

            {

                return new UsernamePasswordAuthenticationToken(user, null, new ArrayList<>());

            }

            return null;

        }

        return null;

    }

}