Registering servlets and filters

It is possible to register Servlet and Filter instances from within an Across module by providing ServletContextInitializer beans. During bootstrap, AcrossWebModule will detect these beans and execute them developing-applications.adoc#bean-order.

For the ServletContext to be customized, the AcrossContext must be bootstrapped during the ServletContext initialization. This is the default when you use @AcrossApplication with an embedded container (Spring Boot application). When deploying to a separate container, you can use AbstractAcrossServletInitializer to achieve the same.

Conditionals

@ConditionalOnConfigurableServletContext can be used to verify that the context is being bootstrapped in a web configuration where the ServletContext allows customization. Likewise @ConditionalOnNotConfigurableServletContext can be used to check the opposite is true.

Example registering the resourceUrlEncodingFilter after all other filters
@Bean
@ConditionalOnProperty(prefix = "acrossWebModule.resources.versioning", value = "enabled", matchIfMissing = true)
@ConditionalOnConfigurableServletContext
public FilterRegistrationBean resourceUrlEncodingFilterRegistration() {
    FilterRegistrationBean registration = new FilterRegistrationBean();
    registration.setName( RESOURCE_URL_ENCODING_FILTER );
    registration.setFilter( new ResourceUrlEncodingFilter() );
    registration.setAsyncSupported( true );
    registration.setMatchAfter( true );
    registration.setUrlPatterns( Collections.singletonList( "/*" ) );
    registration.setDispatcherTypes( DispatcherType.REQUEST, DispatcherType.ERROR, DispatcherType.ASYNC );
    registration.setOrder( Ordered.LOWEST_PRECEDENCE );

    return registration;
}
ServletContextInitializer beans can be ordered but the order between initializers defined inside the Across context and outside the context (on application configuration level) is non deterministic. To enforce overall ordering, it might be easiest to add those initializers to a module using @ModuleConfiguration.