SpringBoot Why does the value of request.getServletPath() change when I register the S1Servlet?

I have the following code snippet.

    @Bean
    public ServletRegistrationBean<S1Servlet> s1Servlet() {
        ServletRegistrationBean<S1Servlet> registrationBean = new ServletRegistrationBean<>(new S1Servlet());
        registrationBean.addUrlMappings("/sub/*");
        registrationBean.setLoadOnStartup(1);
        return registrationBean;
    }

I access the following url:http://localhost:8080/home/sub/st1 (contextpath: home)

When I don't register the ServletRegistrationBean, the result returned by request.getServletPath() is /sub/st1. When I register the ServletRegistrationBean, the result returned by request.getServletPath() is /sub. Why does request.getServletPath() change? I have searched through all the Spring Boot libraries to find how getServletPath() works, but I couldn't find it. I really want to understand how it works and the architecture behind getting the value of request.getServletPath(). Please help me.

Comment From: wilkinsona

This is defined by the Servlet specification. From section 3.5, the servlet path is:

the path section that directly corresponds to the mapping which activated this request. This path starts with a ’/’ character except in the case where the request is matched with the ‘/*’ or ““ pattern, in which case it is an empty string.

With the servlet registration bean, the mapping is /sub/*. The portion of the URL that matches this mapping is /sub/st1 t this is the servlet path. You haven't provided enough information for us to know what the mapping is without the ServletRegistrationBean.

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