ApplicationContextInitializer

1. Overview

In this article, we will learn the ApplicationContextInitializer with an example.
It is a callback interface for initializing a Spring application context prior to being loaded.

Typically used within web applications that require some programmatic initialization of the application context. To learn more about Spring, refer to these articles.

2. ApplicationContextInitializer

The ApplicationContextInitializer allows you to do additional initialization before loading the persistent bean definition (e.g. your application-context.xml). It is essentially code that gets executed before the Spring application context gets completely created.

For example, registering property sources or activating profiles against the context’s environment.

The ApplicationContextInitializer contains a single abstract method initialize:

void initialize(C applicationContext)
//Initialize the given application context.

3. ApplicationContextInitializer example

You must implement the ApplicationContextInitializer to create a custom initializer that can perform additional initialization.

For example, the following code specifies the active profile as dev in your Spring Environment class.

public static class ProfileApplicationContextInitializer implements
		ApplicationContextInitializer<GenericApplicationContext> {
	@Override
	public void initialize(GenericApplicationContext applicationContext) {
		ConfigurableEnvironment appEnvironment = applicationContext.getEnvironment();
		appEnvironment.addActiveProfile("dev");
	}
}

3.1. Spring register bean using ApplicationContextInitializer

You can also register bean using the ApplicationContextInitializer. To know the various other options to register beans programmatically, see this article.

In this class, you can call registerBean and register the bean programmatically.

public class ProgrammaticApplicationContextInitializer implements
		ApplicationContextInitializer<GenericApplicationContext> {
	@Override
	public void initialize(GenericApplicationContext applicationContext) {
		applicationContext.registerBean(CustomBean.class, "Custom  Bean initialization");
	}
}

4. Initialize the ApplicationContextInitalizer

If you are not using the Spring boot, then you can initialize the custom ApplicationContextInitalizer as below:

public static void main(String[] args) {
	AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanfactoryApplication.class);
	ProgrammaticApplicationContextInitializer programmaticApplicationContextInitializer =
			new ProgrammaticApplicationContextInitializer();
	programmaticApplicationContextInitializer.initialize(applicationContext);
}

If you are using Spring Boot, you can register it straightforwardly using either the SpringApplication or SpringApplicationBuilder:

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class BeanfactoryApplication {
 public static void main(String[] args) {
  new SpringApplicationBuilder(BeanfactoryApplication.class)
    .initializers(new ProgrammaticApplicationContextInitializer())
    .run(args);
// or
// You can also add them on your SpringApplication before running it
   application.addInitializers(ProgrammaticApplicationContextInitializer.class);
   application.run(args);
 }
}

You can also initialize them in META-INF/spring.factories

org.springframework.context.ApplicationContextInitializer=\
com.tedblob.ProgrammaticApplicationContextInitializer

You can add it to the web.xml for a Spring web application by declaring a “contextInitializerClasses” context-param and init-param:

<context-param>
    <param-name>contextInitializerClasses</param-name>
    <param-value>com.tedblob.ProgrammaticApplicationContextInitializer</param-value>
</context-param>
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

You can also add it to the external properties file such as application.properties, application,yml, so on:

context.initializer.classes=com.tedblob.ProgrammaticApplicationContextInitializer

5. Conclusion

To sum up, we have learned the ApplicationContextInitializer with examples. You can find code samples of this article in our GitHub repository.