2.spring 4 剖析-BeanDefinitionRegistry详解

前言

上次我们已经聊过了BeanDefinition的实现原理，以及设计思路和如何使用它。
spring工厂中使用的bean实例就是BeanDefinition.

这次的主题就是如何将BeanDefinition进行注册，这次要分析的接口是:BeanDefinitionRegistry

类图

以BeanDefinitionRegistry为中心，展开的类图:

BeanDefinitionRegistry类图

源码分析

BeanDefinitionRegistry

/**
 * 
 * Spring的核心实现是 DefaultListableBeanFactory 和 GenericApplicationContext
*
  * @author Juergen Hoeller
 * @since 26.11.2003
 * @see org.springframework.beans.factory.config.BeanDefinition
 * @see AbstractBeanDefinition
 * @see RootBeanDefinition
 * @see ChildBeanDefinition
 * @see DefaultListableBeanFactory
 * @see org.springframework.context.support.GenericApplicationContext
 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 * @see PropertiesBeanDefinitionReader
 */
public interface BeanDefinitionRegistry extends AliasRegistry {
    void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException;
    void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
    BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException;
    boolean containsBeanDefinition(String beanName);
    String[] getBeanDefinitionNames();
    int getBeanDefinitionCount();
    boolean isBeanNameInUse(String beanName);
}

AliasRegistry这个接口的意思是可以给BeanDefinition起个别名，然后注册使用。

spring 提供给了我们一个简单的类进行测试--SimpleBeanDefinitionRegistry

SimpleBeanDefinitionRegistry

public class SimpleBeanDefinitionRegistry extends SimpleAliasRegistry implements BeanDefinitionRegistry {
    private final Map beanDefinitionMap = new ConcurrentHashMap(64);
    @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "'beanName' must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");
        this.beanDefinitionMap.put(beanName, beanDefinition);
    }
//其他代码省略
}

它仅仅使用了Map进行了存储。

可以做个小实验试一下:

public class Test {

    public static void main(String[] args) throws Exception {
        BeanDefinitionRegistry beanDefinitionRegistry = new SimpleBeanDefinitionRegistry();
        AnnotatedGenericBeanDefinition genericBeanDefinition = new AnnotatedGenericBeanDefinition(Test.class);
        beanDefinitionRegistry.registerBeanDefinition("springBean",genericBeanDefinition);
        System.out.println(beanDefinitionRegistry.isBeanNameInUse("springBean"));
    }
}

输出:

true

DefaultListableBeanFactory

spring 推荐给我们，DefaultListableBeanFactory和GenericApplicationContext才是核心。

我们看一下DefaultListableBeanFactory:

public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory
        implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable {
private final Map beanDefinitionMap = new ConcurrentHashMap(64);

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;

        oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
        }
        else {
            this.beanDefinitionNames.add(beanName);
            this.manualSingletonNames.remove(beanName);
            this.frozenBeanDefinitionNames = null;
        }
        this.beanDefinitionMap.put(beanName, beanDefinition);

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }
//其他方法省略
}

可以看出来它依然使用了Map进行存储(变量是beanDefinitionMap)，只不过验证流程比较缜密了。

GenericApplicationContext

public class GenericApplicationContext extends AbstractApplicationContext implements BeanDefinitionRegistry {
    private final DefaultListableBeanFactory beanFactory;
    private ResourceLoader resourceLoader;
    private boolean refreshed = false;
    public GenericApplicationContext() {
        this.beanFactory = new DefaultListableBeanFactory();
    }
        @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        this.beanFactory.registerBeanDefinition(beanName, beanDefinition);
    }
//其他代码省略
}

看到构造方法中的this.beanFactory = new DefaultListableBeanFactory(); 就发现，其实GenericApplicationContext使用的注册bean依然是使用DefaultListableBeanFactory的实现原理。