UrlHandlerFilter should not strip the trailing slash from the contextPath URL

[bdshadow]

Although #33444 has been fixed for root URLs, it looks like there is still a problem with the UrlHandlerFilter when server.servlet.contextPath is specified.

Here is a minimal application to reproduce it: https://github.com/bdshadow/SpringTrailingSlashTestProject

server.servlet.contextPath=/myApp

And use the following UrlHandlerFilter:

        UrlHandlerFilter filter = UrlHandlerFilter
            .trailingSlashHandler("/**").wrapRequest()
            .build();

And in this case, both http://localhost:8080/myApp/greeting and http://localhost:8080/myApp/greeting work fine, however,
http://localhost:8080/myApp and http://localhost:8080/myApp/ don't and return 404.

Controller for the root looks like this:

@RestController
@RequestMapping("/")
public class MyController {
    @GetMapping(value = {"/", "greeting"})
    public String greeting() {
        return "Hello world!";
    }
}

[rstoyanchev]

You can map with "" which handles "/" as well. For example this works:

@RestController
public class MyController {
    @GetMapping(value = {"", "greeting"})
    public String greeting() {
        return "Hello world!";
    }
}

However, if you configure UrlHandlerFilter to redirect, it would send "/myApp/" to "/myApp", which would work for the request mappings, but Tomcat redirects "/myApp" back to "/myApp/". And in any case, I think the UrlHandlerFilter should makes checks on the pathWithinApplication, excluding the contextPath.