Add a Servlet Filter in a Spring Boot application

Question

I\'d like to have ETag suport. For this purpose there is a ShallowEtagHeaderFilter which does all the work. How can I add it without declaring it in my we

Answer 1

When using Spring Boot

As mentioned in the reference documentation, the only step needed is to declare that filter as a Bean in a configuration class, that's it!

@Configuration
public class WebConfig {

  @Bean
  public Filter shallowEtagHeaderFilter() {
    return new ShallowEtagHeaderFilter();
  }
}

When using Spring MVC

You're probably already extending a WebApplicationInitializer. If not, then you should convert your webapp configuration from a web.xml file to a WebApplicationInitializer class.

If your context configuration lives in XML file(s), you can create a class that extends AbstractDispatcherServletInitializer - if using configuration classes, AbstractAnnotationConfigDispatcherServletInitializer is the proper choice.

In any case, you can then add Filter registration:

  @Override
  protected Filter[] getServletFilters() {
    return new Filter[] {
      new ShallowEtagHeaderFilter();
    };
  }

Full examples of code-based Servlet container initialization are available in the Spring reference documentation.

Answer 2

A bit late answer.

My solution was to create custom annotation:

import org.springframework.core.annotation.AliasFor;
import org.springframework.stereotype.Component;

// ...

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Component
public @interface Filter {

    @AliasFor(annotation = Component.class, attribute = "value")
    String value() default "";

}

And then simply apply it to the filter implementations:

@Filter
public class CustomFilter extends AbstractRequestLoggingFilter {

    @Override
    protected void beforeRequest(HttpServletRequest request, String message) {
        logger.debug("before req params:", request.getParameterMap());
    }

    @Override
    protected void afterRequest(HttpServletRequest request, String message) {
        logger.debug("after req params:", request.getParameterMap());
    }
}

See more: @AliasFor, Spring custom annotations question