BeanFactory和ApplicationContext的关系

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

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">
<bean name="repository" class="ioc.overview.repository.Repository" autowire="byType"></bean>
</beans>

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

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);
}

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。