BeanFactory和ApplicationContext的关系

使用版本为 Spring Framework 5.2.2.RELEASE，来探索BeanFactory和ApplicationContext的关系。

开始

首先创建了Repository类，有两个属性，类型为 BeanFactory 和 ApplicationContext

public class Repository {

  private BeanFactory beanFactory;

  private ApplicationContext applicationContext;

  public ApplicationContext getApplicationContext() {
    return applicationContext;
  }

  public void setApplicationContext(ApplicationContext applicationContext) {
    this.applicationContext = applicationContext;
  }

  public BeanFactory getBeanFactory() {
    return beanFactory;
  }

  public void setBeanFactory(BeanFactory beanFactory) {
    this.beanFactory = beanFactory;
  }
}

创建配置bean的xml

创建测试类：

public class DependencyInjectionDemo {

  public static void main(String[] args) {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("classpath:/injection-context.xml");
    Repository repository = beanFactory.getBean("userRepository", Repository.class);
      
    System.out.println("injected beanFactory == main beanFactory: " + (repository.getBeanFactory() == beanFactory));

    System.out.println("injected applicationContext == main beanFactory: " + (repository.getApplicationContext() == beanFactory));
  }
}

打印如下：

injected beanFactory == main beanFactory: false
injected applicationContext == main beanFactory: true

为什么 beanFactory 不等于 beanFactory 呢？

看看类的继承关系

ClassPathXmlApplicationContext继承自 AbstractApplicationContext 。

// AbstractApplicationContext 实现了 ApplicationContext 接口
public abstract class AbstractApplicationContext extends DefaultResourceLoader
		implements ConfigurableApplicationContext {
}
public interface ConfigurableApplicationContext extends ApplicationContext, Lifecycle, Closeable {
}
// ApplicationContext 是 BeanFactory的子接口
public interface ApplicationContext extends ListableBeanFactory...
public interface ListableBeanFactory extends BeanFactory {}

再来看 ConfigurableApplicationContext 中，声明了一个获取 beanFactory 的方法：

ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException;

自己就是 beanFactory，为什么还要声明这个方法呢？

接着，来看这个方法的实现：

AbstractRefreshableApplicationContext#getBeanFactory

public abstract class AbstractRefreshableApplicationContext extends AbstractApplicationContext {

	/** Bean factory for this context. */
	@Nullable
	private DefaultListableBeanFactory beanFactory;

	@Override
	public final ConfigurableListableBeanFactory getBeanFactory() {
		synchronized (this.beanFactoryMonitor) {
			if (this.beanFactory == null) {
				throw new IllegalStateException("BeanFactory not initialized or already closed - " + "call 'refresh' before accessing beans via the ApplicationContext");
			}
			return this.beanFactory;
		}
	}

 

再来看看 getBean 的实现，他使用了组合的方式，使用 beanFactory 对象进行获取 bean。

	@Override
	public  T getBean(String name, Class requiredType) throws BeansException {
		assertBeanFactoryActive();
		return getBeanFactory().getBean(name, requiredType);
	}

总结

BeanFactory 是底层的Ioc容器，ApplicationContext 继承了它，并增加了一些特性。在实现方面，ApplicationContext 组合了一个 BeanFactory 的实现，使用这个实现对象来完成一些操作。