文章目录

1 BeanDefinition
- 1.1 Spring Bean 读取解析配置信息
- - 1.1.1 XML 配置的处理主要使用的事例
  - 1.1.2 注解 BeanDefinition 解析示例
- 1.2 spring bean 注册阶段
- 1.3 Spring BeanDefinition 合并阶段
- - 1.3.1 BeanDefinition 合并示例
  - 1.3.2 源码分析

1 BeanDefinition

在spring bean创建过程依赖 BeanDefinition 中的信息处理bean的生产。BeanDefinition 是 Spring Framework 中定义 Bean 的配置元信息接口
在这里插入图片描述
在处理配置文件生成BeanDefinition主要经过：Spring Bean 读取解析配置信息、spring bean 注册阶段、Spring BeanDefinition 合并阶段

1.1 Spring Bean 读取解析配置信息

spring bean的配置信息分为：

面向资源
- XML配置的处理主要使用：XmlBeanDefinitionReader
- Properties 资源配置：PropertiesBeanDefinitionReader
面向注解
- 面向注解 BeanDefinition 解析： AnnotatedBeanDefinitionReader

1.1.1 XML 配置的处理主要使用的事例

这里主要基于xml中的构造方法处理：

public class UserHolder {
 
    private User user;
 
    public UserHolder() {
    }
 
    public UserHolder(User user) {
        this.user = user;
    }
 
    public User getUser() {
        return user;
    }
 
    public void setUser(User user) {
        this.user = user;
    }
 
    @Override
    public String toString() {
        return "UserHolder{" +
                "user=" + user +
                '}';
    }
}

/**
 * 基于 XML 资源的依赖 Constructor 注入示例
 */
public class XmlDependencyConstructorInjectionDemo {
 
    public static void main(String[] args) {
 
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
 
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
 
        String xmlResourcePath = "classpath:/META-INF/dependency-constructor-injection.xml";
        // 加载 XML 资源，解析并且生成 BeanDefinition
        beanDefinitionReader.loadBeanDefinitions(xmlResourcePath);
        // 依赖查找并且创建 Bean
        UserHolder userHolder = beanFactory.getBean(UserHolder.class);
        System.out.println(userHolder);
 
    }
}

xml的配置文件

<?xml version="1.0" encoding="UTF-8"?>
<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 id="user" class="org.geekbang.thinking.in.spring.ioc.overview.domain.User">
        <property name="id" value="1"/>
        <property name="name" value="测试"/>
        <property name="city" value="test"/>
        <property name="workCities" value="BEIJING,HANGZHOU"/>
        <property name="lifeCities">
            <list>
                <value>BEIJING</value>
                <value>SHANGHAI</value>
            </list>
        </property>
        <property name="configFileLocation" value="classpath:/META-INF/user-config.properties"/>
    </bean>
 
    <bean id="superUser" class="org.geekbang.thinking.in.spring.ioc.overview.domain.SuperUser" parent="user"
          primary="true">
        <property name="address" value="杭州"/>
    </bean>
 
 
    <bean class="org.geekbang.thinking.in.spring.ioc.dependency.injection.UserHolder">
        <constructor-arg name="user" ref="superUser" />
    </bean>
 
</beans>

1.1.2 注解 BeanDefinition 解析示例

使用AnnotatedBeanDefinitionReader 来处理注解的类生成BeanDefinition 并注入到容器中

public class AnnotatedBeanDefinitionParsingDemo {
 
    public static void main(String[] args) {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        // 基于 Java 注解的 AnnotatedBeanDefinitionReader 的实现
        AnnotatedBeanDefinitionReader beanDefinitionReader = new AnnotatedBeanDefinitionReader(beanFactory);
        int beanDefinitionCountBefore = beanFactory.getBeanDefinitionCount();
        // 注册当前类（非 @Component class）
        beanDefinitionReader.register(AnnotatedBeanDefinitionParsingDemo.class);
        int beanDefinitionCountAfter = beanFactory.getBeanDefinitionCount();
        int beanDefinitionCount = beanDefinitionCountAfter - beanDefinitionCountBefore;
        System.out.println("已增加加载 BeanDefinition 数量：" + beanDefinitionCount);
        // 普通的 Class 作为 Component 注册到 Spring IoC 容器后，通常 Bean 名称为 annotatedBeanDefinitionParsingDemo
        // Bean 名称生成来自于 BeanNameGenerator，注解实现 AnnotationBeanNameGenerator
        AnnotatedBeanDefinitionParsingDemo demo = beanFactory.getBean("annotatedBeanDefinitionParsingDemo",
                AnnotatedBeanDefinitionParsingDemo.class);
        System.out.println(demo);
    }
}

1.2 spring bean 注册阶段

在步骤一中生成的 BeanDefinition 需要注入到容器中
BeanDefinition 注册接口：BeanDefinitionRegistry
注册BeanDefinition其实就是把 BeanDefinition信息放入map中

注册到一个map中

private final Map<String, RootBeanDefinition> mergedBeanDefinitions = new ConcurrentHashMap<>(256);

1.3 Spring BeanDefinition 合并阶段

在合并阶段主要解决Bean继承时子类合并父类公共属性问题：

可以把 父BeanDefinition的信息合并到子BeanDefinition中；合并中的BeanDefinition主要依靠下面三个子类实现的

ChildBeanDefinition：要指定父类。实例化的时候一定要是父BeanDefinition，永远只能作为一个子BeanDefinition。
RootBeanDefinition： spring 2.5的首选一般表示。作为父beanDefinition出现也可以作为普遍的bd 但是不能设置父beanDefinition即不能作为子bd。
GenericBeanDefinition：spring 2.5 以后出现的常用的可以替换 ChildBeanDefinition 但是不能替换 RootBeanDefinition。可以完成RootBeanDefinition和ChildBeanDefinition 两种的功能。

合并过程一般是把 GenericBeanDefinition的处理合并成 RootBeanDefinition。

1.3.1 BeanDefinition 合并示例

public class MergedBeanDefinitionDemo {
 
    public static void main(String[] args) {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        // 基于 XML 资源 BeanDefinitionReader 实现
        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
        String location = "META-INF/dependency-lookup-context.xml";
        // 基于 ClassPath 加载 XML 资源
        Resource resource = new ClassPathResource(location);
        // 指定字符编码 UTF-8
        EncodedResource encodedResource = new EncodedResource(resource, "UTF-8");
        int beanNumbers = beanDefinitionReader.loadBeanDefinitions(encodedResource);
        System.out.println("已加载 BeanDefinition 数量：" + beanNumbers);
        // 通过 Bean Id 和类型进行依赖查找
        User user = beanFactory.getBean("user", User.class);
        System.out.println(user);
 
        User superUser = beanFactory.getBean("superUser", User.class);
        System.out.println(superUser);
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:context="http://www.springframework.org/schema/context"
        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
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
 
<!--    <context:annotation-config/>-->
 
<!--    <context:component-scan base-package="org.acme" />-->
 
    <!-- Root BeanDefinition 不需要合并，不存在 parent -->
    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 经过合并后 GenericBeanDefinition 变成 RootBeanDefinition -->
    <bean id="user" class="org.geekbang.thinking.in.spring.ioc.overview.domain.User">
        <property name="id" value="1"/>
        <property name="name" value="小马哥"/>
        <property name="city" value="HANGZHOU"/>
        <property name="workCities" value="BEIJING,HANGZHOU"/>
        <property name="lifeCities">
            <list>
                <value>BEIJING</value>
                <value>SHANGHAI</value>
            </list>
        </property>
        <property name="configFileLocation" value="classpath:/META-INF/user-config.properties"/>
    </bean>
 
    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 合并后 GenericBeanDefinition 变成 RootBeanDefinition，并且覆盖 parent 相关配置-->
    <!-- primary = true , 增加了一个 address 属性 -->
    <bean id="superUser" class="org.geekbang.thinking.in.spring.ioc.overview.domain.SuperUser" parent="user"
          primary="true">
        <property name="address" value="杭州"/>
    </bean>
 
    <bean id="objectFactory" class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
        <property name="targetBeanName" value="user"/>
    </bean>
 
</beans>

执行结果。我们可以看到 SuperUser中包括的其父类 User的相关属性

已加载 BeanDefinition 数量：3
User{id=1, name='小马哥', city=HANGZHOU, workCities=[BEIJING, HANGZHOU], lifeCities=[BEIJING, SHANGHAI], configFileLocation=class path resource [META-INF/user-config.properties], company=null, context=null, contextAsText='null', beanName='user'}
SuperUser{address='杭州'} User{id=1, name='小马哥', city=HANGZHOU, workCities=[BEIJING, HANGZHOU], lifeCities=[BEIJING, SHANGHAI], configFileLocation=class path resource [META-INF/user-config.properties], company=null, context=null, contextAsText='null', beanName='superUser'}

1.3.2 源码分析

合并 BeanDefinition 操作在 AbstractBeanFactory中发doGetBean()方法中的
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

protected RootBeanDefinition getMergedBeanDefinition(
			String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
			throws BeanDefinitionStoreException {
 
		synchronized (this.mergedBeanDefinitions) {
			RootBeanDefinition mbd = null;
 
			// Check with full lock now in order to enforce the same merged instance.
			if (containingBd == null) {
				mbd = this.mergedBeanDefinitions.get(beanName);
			}
 
			if (mbd == null) {
				if (bd.getParentName() == null) {
					// Use copy of given root bean definition.
					if (bd instanceof RootBeanDefinition) {
						mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
					}
					else {
						mbd = new RootBeanDefinition(bd);
					}
				}
				else {
					// Child bean definition: needs to be merged with parent.
					BeanDefinition pbd;
					try {
						String parentBeanName = transformedBeanName(bd.getParentName());
						if (!beanName.equals(parentBeanName)) {
							//TODO 这里这次在去合并父类的 父类 这里使用递归的处理
							pbd = getMergedBeanDefinition(parentBeanName);
						}
						else {
							BeanFactory parent = getParentBeanFactory();
							if (parent instanceof ConfigurableBeanFactory) {
								pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName);
							}
							else {
								throw new NoSuchBeanDefinitionException(parentBeanName,
										"Parent name '" + parentBeanName + "' is equal to bean name '" + beanName +
										"': cannot be resolved without an AbstractBeanFactory parent");
							}
						}
					}
					catch (NoSuchBeanDefinitionException ex) {
						throw new BeanDefinitionStoreException(bd.getResourceDescription(), beanName,
								"Could not resolve parent bean definition '" + bd.getParentName() + "'", ex);
					}
					// Deep copy with overridden values.
					//最终的返回对象 合并后的对象
					mbd = new RootBeanDefinition(pbd);
					mbd.overrideFrom(bd);
				}
 
				// Set default singleton scope, if not configured before.
				if (!StringUtils.hasLength(mbd.getScope())) {
					mbd.setScope(RootBeanDefinition.SCOPE_SINGLETON);
				}
 
				// A bean contained in a non-singleton bean cannot be a singleton itself.
				// Let's correct this on the fly here, since this might be the result of
				// parent-child merging for the outer bean, in which case the original inner bean
				// definition will not have inherited the merged outer bean's singleton status.
				if (containingBd != null && !containingBd.isSingleton() && mbd.isSingleton()) {
					mbd.setScope(containingBd.getScope());
				}
 
				// Cache the merged bean definition for the time being
				// (it might still get re-merged later on in order to pick up metadata changes)
				if (containingBd == null && isCacheBeanMetadata()) {
					this.mergedBeanDefinitions.put(beanName, mbd);
				}
			}
 
			return mbd;
		}
	}