Overriding Bean Configuration with annotations

[dcompiled]

Use case: I have my container configured via classpath scanning @ComponentScan. For my test configuration I need the ability to mock specific beans.

Due to the order of loading, beans loaded via classpath scan are not overriding properly when using @Configuration. The following code samples demonstrate the problem. BaseExample.java shows how it is possible to override beans via configuration. ScanExample.java shows that overriding a bean that was loaded via @ComponentScan is skipped (see final note).

// BaseExample.java

package com.glassworks.mock;

import org.mockito.Mockito;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.google.common.base.Joiner;

public class BaseExample {
	private static final Logger log = LoggerFactory.getLogger(BaseExample.class);
	private static AnnotationConfigApplicationContext ctx;
	
	public static void main(String args[]) {
		ctx = new AnnotationConfigApplicationContext(Config.class, OverrideConfig.class);
		
		String beans[] = ctx.getBeanDefinitionNames();
		log.info("{} beans found: {}", beans.length, Joiner.on(",").join(beans));
		
		for(String bean : beans) {
			log.info("{}: {}", bean, ctx.getBean(bean));
		}
	}

	@Configuration
	public static class Config {
		@Bean
		public AccountDao accountDao() {
			log.debug("Creating accountDao [Config]");
			return new AccountDao();
		}
	}
	
	@Configuration
	public static class OverrideConfig {
		@Bean
		public Object accountDao() {
			log.debug("Creating accountDao [OverrideConfig]");
			return Mockito.mock(AccountDao.class);
		}
	}
		
}

Output:
21:05 INFO | com.glassworks.mock.BaseExample | accountDao: Mock for AccountDao, hashCode: 666537607

// ScanExample.java

package com.glassworks.mock;

import org.mockito.Mockito;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

import com.google.common.base.Joiner;

public class ScanExample {
	private static final Logger log = LoggerFactory.getLogger(ScanExample.class);
	private static AnnotationConfigApplicationContext ctx;
	
	public static void main(String args[]) {
		ctx = new AnnotationConfigApplicationContext(Config.class, OverrideConfig.class);
		
		String beans[] = ctx.getBeanDefinitionNames();
		log.info("{} beans found: {}", beans.length, Joiner.on(",").join(beans));
		
		for(String bean : beans) {
			log.info("{}: {}", bean, ctx.getBean(bean));
		}
	}

	@Configuration
	@ComponentScan("com.glassworks.services")
	public static class Config {
		
	}
	
	@Configuration
	public static class OverrideConfig {
		@Bean
		public AccountDao accountDao() {
			log.debug("Creating accountDao [OverrideConfig]");
			return Mockito.mock(AccountDao.class);
		}
	}
		
}

Output:
21:08 INFO | com.glassworks.mock.ScanExample | accountDao: com.glassworks.services.AccountDao@48805ebb

// AccountDao.java
package com.glassworks.services;

import org.springframework.stereotype.Repository;

@Repository
public class AccountDao {
	
}

Note
Its worth noting on that with logging set to debug, Spring indicates that it is skipping over the definition. This appears to be a bug.

21:09 DEBUG | o.s.c.a.ConfigurationClassBeanDefinitionReader | Skipping loading bean definition for [BeanMethod:name=accountDao,declaringClass=com.glas sworks.mock.ScanExample$OverrideConfig]: a definition for bean 'accountDao' already exists. This is likely due to an override in XML.

[Paul Newport]

There's an open Jira for this problem:

https://jira.springsource.org/browse...mment-tabpanel

It might be worth voting on if you have a Jira login for the above, as the issue was raised over two years ago.