Simple demo application showcasing the performance impact of ResourceUrlEncodingFilter when processing URLs using HttpServletResponse#encodeURL.
Just run the tests or start the application and navigate to http://localhost:8080/?links=1. Increase the value of 'links' and observe the CPU impact.
Start the application with -Dspring.profiles.active=fix. With this profile active, the default configuration will be replaced, improving the performance significantly for pages with many links.
This is achieved by setting spring.web.resources.add-mappings to false and registering custom resource handlers (e.g. /css/** -> classpath:/static/css/), removing the need to check whether any other link passed to HttpServletResponse#encodeURL is a static resource.
See ResourceRegistrationConfig for the resource handlers.
When using Thymeleaf with enabled ResourceUrlEncodingFilter, this happends for every usage of @{...} to build URLs. The problem occurs when PathResourceResolver is checking any URL passed to HttpServletResponse#encodeURL against a list of possible static resources, throwing a FileNotFoundException for each miss.