Spring root and servlet context with Java config

Question

I'm running a Spring application in a Servlet 3.0+ environment to programmatically configure the servlet context using all Java configuration. My question (with details below): how is a project structured to support component scanning for both root and web application contexts without duplicating component initialization?

As I understand it, there are two contexts in which to register Spring beans. First, the root context is where non-servlet-related components go. For example batch jobs, DAOs, etc. Second, the servlet context is where servlet-related components go such as controllers, filters, etc.

I've implemented a WebApplicationInitializer to register these two contexts just as the JavaDoc in WebApplicationInitializer specifies with a AppConfig.class and DispatcherConfig.class.

I want both to automatically find their respective components so I've added @ComponentScan to both (which is resulting in my Hibernate entities being initiated twice). Spring finds these components by scanning some specified base package. Does that mean I need to put all my DAO-related objects in a separate package from the controllers? If so, that'd be quite inconvenient as I generally like to package by functionality (as opposed to type).

Code snippets...

WebApplicationInitializer:

public class AppInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext container) throws ServletException {
        // Create the 'root' Spring application context
        AnnotationConfigWebApplicationContext rootContext =
                new AnnotationConfigWebApplicationContext();
        rootContext.register(AppConfig.class);

        // Manage the lifecycle of the root application context
        container.addListener(new ContextLoaderListener(rootContext));

        // Create the dispatcher servlet's Spring application context
        AnnotationConfigWebApplicationContext dispatcherContext =
                new AnnotationConfigWebApplicationContext();
        dispatcherContext.register(WebAppConfig.class);

        // Register and map the dispatcher servlet
        ServletRegistration.Dynamic dispatcher =
                container.addServlet("dispatcher", new DispatcherServlet(dispatcherContext));
        dispatcher.setLoadOnStartup(1);
        dispatcher.addMapping("/");
    }

}

AppConfig:

@Configuration
@ComponentScan
public class AppConfig {
}

WebAppConfig:

@Configuration
@EnableWebMvc
@EnableSpringDataWebSupport
@ComponentScan(basePackageClasses = AppConfig.class)
public class WebAppConfig extends WebMvcConfigurerAdapter {
}

M. Deinum M. Deinum · Accepted Answer · 2015-02-03T11:03:53

Just define what you want to scan for in each configuration. In general your root configuration should scan for everything but @Controllers and your web configuration should only detect @Controllers.

You can accomplish this by using the includeFilters and excludeFilters attributes of the @ComponentScan annotation. When using include filters, in this case, you also need to disable using the default filters by setting useDefaultFilters to false.

@Configuration
@ComponentScan(excludeFilters={@Filter(org.springframework.stereotype.Controller.class)})
public class AppConfig {}

And for your WebConfig

@Configuration
@EnableWebMvc
@EnableSpringDataWebSupport
@ComponentScan(basePackageClasses = AppConfig.class, useDefaultFilters=false, includeFilters={@Filter(org.springframework.stereotype.Controller.class)})
public class WebAppConfig extends WebMvcConfigurerAdapter {}

In addition, you need to import the @Filter annotation:

import static org.springframework.context.annotation.ComponentScan.Filter;

Spring root and servlet context with Java config

2 Answers