How do you override a spring bean defined in xml using Annotations?

Question

I have an existing bean overrideBean defined in spring.xml which I would like to override using annotations. I have tried the following to override the bean:

@Configuration
@ImportResource({"/spring.xml"})
public class Main {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(DdwMain.class);

        Object o = context.getBean("overrideBean");
        // o should be null but it is not
    }

    @Bean(name="overrideBean")
    public OverrideBean overrideBean() {
        return null;
    }

}

Using the above code the bean from the spring.xml config is always instantiated and returned by the context.getBean call.

The bean can be overridden by including another XML config file in the @ImportResource however I would prefer to find a solution using annotations would be cleaner.

Answer 1

I'm working in an older app (spring 3.1.1) that's configured via xml, but I needed to shuffle some config around for testing without deviating too far from the production config. My approach is to use a BeanPostProcessor.

package myapp.test;

import javax.servlet.ServletContext;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.context.annotation.ImportResource;
import org.springframework.mock.web.MockServletContext;
import org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer;

import myapp.spring.config.ComplexSpringConfiguration;

/**
 * Closely resembles production configuration for testing
 * @author jim
 */
@Configuration
@ImportResource("file:src/main/webapp/WEB-INF/spring-servlet.xml")
@Import(ComplexSpringConfiguration.class)
public class TestConfig {
    final Logger logger = LoggerFactory.getLogger(getClass());

    static {
        System.setProperty("env.test", "system");
    }

    //Override templateLoaderPath with something amenable to testing
    @Bean
    public BeanPostProcessor beanPostProcessor(){
        return new BeanPostProcessor(){
            @Override
            public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException  {
                //Override templateLoaderPath with something amenable to testing
                if(beanName.equals("freemarkerConfig")) {
                    logger.debug("overriding bean with name:" + beanName);
                    FreeMarkerConfigurer fc = new FreeMarkerConfigurer();
                    fc.setTemplateLoaderPath("file:src/main/webapp/WEB-INF/freemarker");
                    bean = fc;
                }
                return bean;
            }

            @Override
            public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
                return bean;
           }  
       };
    }

    @Bean
    public ServletContext servletContext(){
        MockServletContext mockContext = new MockServletContext();
        mockContext.setContextPath("/myapp");
        return mockContext;
    }
}

Answer 2

Usually xml-registered beans have precedence. So you can override annotated beans with xml-configured ones but you are trying to do it the other way around. Can you not use a different bean name and select it among multiple candidates by using the @Qualifier annotation?

Most of the time combining xml with autoscanning is error-prone.