ResourceUrlEncodingFilter cache misses are expensive

[dsyer]

A PetClinic user noticed this (spring-projects/spring-petclinic#1732). For me it's a 2x throughput degradation on the home page of PetClinic, for the user that reported the issue it was 4x. The problem seems to be that ResourceUrlEncodingFilter has a CachingResourceResolver in it that works great for actual classpath resources. Conversely, links that are not static resources are cache misses, and they have to be checked every time in case they are, after all, on the classpath (e.g. links to other pages in the app).

[maio]

Hello,

we also encountered this issue in our backoffice app which uses webjars-locator-lite, and displays tables with few hundreds of rows where each has multiple actions for which links get generated in Thymeleaf using <a href="@{/an/app/path/..}"> syntax. I would expect zero performance impact as these links have nothing to do with webjars, but instead we see a lot of CPU time being spent in LiteWebJarsResourceResolver.

To be precise time is being spent in org.springframework.web.servlet.resource.LiteWebJarsResourceResolver#resolveUrlPathInternal

99% of this 7 plus seconds were spent in following methods (stacktrace):

org.springframework.web.servlet.resource.LiteWebJarsResourceResolver#resolveUrlPathInternal
org.springframework.web.servlet.resource.DefaultResourceResolverChain#resolveUrlPath
org.springframework.web.servlet.resource.AbstractResourceResolver#resolveUrlPath
org.springframework.web.servlet.resource.PathResourceResolver#resolveUrlPathInternal
org.springframework.web.servlet.resource.PathResourceResolver#getResource(java.lang.String, jakarta.servlet.http.HttpServletRequest, java.util.List<? extends org.springframework.core.io.Resource>)

BTW we are including webjars using HTML like this:

<link rel="stylesheet" th:href="@{/webjars/bootstrap/dist/css/bootstrap.css}">

So I would expect locator to do it's magic just for URLs which start with /webjars, but it seems to affect/process all the URLs which is problematic for any app that generates links to many unique URLs (e.g. link to transaction/user/whatever detail which contains ID).

[dsyer]

The problem isn't the webjars locator per se though, it's a side effect of Spring Boot enabling a bunch of stuff including that. You might be able to workaround the issue by setting spring.web.resources.chain.cache=false.