Spring Boot - Filter not applied for noHandlerFoundException

Question

I tried to implement a filter following this answer:

How do I minify dynamic HTML responses in Spring?

This works very good, however, this filter does not work when the error 404 is thrown. Why not? And how do I apply this filter also for my 404-error page?

Solution:

Using the following code:

@ControllerAdvice
@Order(HIGHEST_PRECEDENCE)
public class NotFoundException {

     @ExceptionHandler(NoHandlerFoundException.class)
     public String noHandlerFoundException() {
          // provide information to view
          return "error";
     }
}

with the application.properties:

 spring.web.resources.add-mappings=false
 spring.mvc.throw-exception-if-no-handler-found=true 

allows the redirection to the error page and the filter is applied. However, the warning: "No mapping for GET /css/styles.css" (and all other static resources) is logged. Registering a ResourceHandler with:

 resourceHandlerRegistry.addResourceHandler("/css/**").addResourceLocations("classpath:/static/css/");
 // register resource handler for other static content

solved this. See also issues: #7653 (spring-boot) and #29491 (spring-framework) in the spring-projects, which seem related. Thank you!

Answer 1

A 404 is not a “normal“ exception type error in Spring Boot.

To turn it into a handleable exception add the following to application.properties

spring.mvc.throw-exception-if-no-handler-found=true

This may be sufficient to cause the minify filter to be hit.

Otherwise add an exception handler for the not found to apply the CharResponseWrapper or other mechanism to provide minified response.