BeanMethodPolymorphismTests.java

package org.springframework.context.annotation;

import static org.hamcrest.CoreMatchers.equalTo;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.assertTrue;
import static org.junit.Assert.fail;

import org.junit.Test;
import org.springframework.beans.factory.parsing.BeanDefinitionParsingException;

/**
 * Tests regarding overloading and overriding of bean methods.
 * Related to SPR-6618.
 *
 * Bean-annotated methods should be able to be overridden, just as any regular
 * method. This is straightforward.
 *
 * Bean-annotated methods should be able to be overloaded, though supporting this
 * is more subtle. Essentially, it must be unambiguous to the container which bean
 * method to call.  A simple way to think about this is that no one Configuration
 * class may declare two bean methods with the same name.  In the case of inheritance,
 * the most specific subclass bean method will always be the one that is invoked.
 *
 * @author Chris Beams
 */
public class BeanMethodPolymorphismTests {

	@Test
	public void beanMethodOverloadingWithoutInheritance() {
		@SuppressWarnings("unused")
		@Configuration class Config {
			@Bean String aString() { return "na"; }
			@Bean String aString(Integer dependency) { return "na"; }
		}
		try {
			new AnnotationConfigApplicationContext(Config.class);
			fail("expected bean method overloading exception");
		} catch (BeanDefinitionParsingException ex) {
			assertTrue(ex.getMessage(), ex.getMessage().contains("2 overloaded @Bean methods named 'aString'"));
		}
	}

	@Test
	public void beanMethodOverloadingWithInheritance() {
		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(SubConfig.class);
		assertThat(ctx.getBean(String.class), equalTo("overloaded5"));
	}
	static @Configuration class SuperConfig {
		@Bean String aString() { return "super"; }
	}
	static @Configuration class SubConfig {
		@Bean Integer anInt() { return 5; }
		@Bean String aString(Integer dependency) { return "overloaded"+dependency; }
	}
	
	/**
	 * When inheritance is not involved, it is still possible to override a bean method from
	 * the container's point of view. This is not strictly 'overloading' of a method per se,
	 * so it's referred to here as 'shadowing' to distinguish the difference.
	 */
	@Test
	public void beanMethodShadowing() {
		AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(ShadowConfig.class);
		assertThat(ctx.getBean(String.class), equalTo("shadow"));
	}
	@Import(SubConfig.class)
	static @Configuration class ShadowConfig {
		@Bean String aString() { return "shadow"; }
	}

}