【Spring源码深度解析学习系列】复杂标签属性解析（四）

一、创建用于属性承载的BeanDefinition

BeanDefiniton是一个接口，在Spring中存在三种实现：RootBeanDefinition、ChildBeanDefinition、GenericBeanDefiniton.三种实现均继承了AbstractBeanFactory，其中BeanDefinition是配置文件<bean>元素标签在容器中的内部表示形式。<bean>元素拥有class、scope、lazy-init等配置属性，BeanDefinition则提供了相应的beanClass、scope、lazyInit属性，BeanDefinition和<bean>中的属性是一一对应的。其中RootBeanDefinition是最常用的实现类，它对应一般性的<bean>元素标签，GenericBeanDefiniton是自2.5版本以后新加入的bean文件配置属性定义类，是一站式服务类。

在配置文件中可以定义父<bean>和子<bean>。父<bean>用RootBeanDefinition表示，而子<bean>用CgildBeanDefiniton表示，而没有父<bean>的,bea>就使用RootBeanDefinition表示。AbstractBeanDefinition对两者共同的类信息进行抽象。

Spring通过BeanDefinition将配置文件中的<bean>配置信息转换为容器的内部表示，并将这些BeanDefiniton注册到BeanDefinitonRegistry中。Spring容器的BeanDefinitonRegistry就像是Spring配置信息的内存数据库，主要是以map的形式保存，后续操作直接从BeanDefinitionRegistry中读取配置信息。

1、要解析属性首先要创建用于承载属性的实例，也就是创建GenericBeanDefiniton类型的实例。

2、解析各种属性

当我们创建了bean信息的承载实例后，变可以进行bean信息的各种属性解析了，首先我们进入parseBeanDefinitionAttribute方法。该方法是对element所有元素属性进行解析。

二、AbstractBeanDefinition属性

public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor
		implements BeanDefinition, Cloneable {

	/**
	 * Constant for the default scope name: {@code ""}, equivalent to singleton
	 * status unless overridden from a parent bean definition (if applicable).
	 * bean的作用范围，对应bean属性scope
	 */
	public static final String SCOPE_DEFAULT = "";

	/**
	 * Constant that indicates no autowiring at all.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_NO = AutowireCapableBeanFactory.AUTOWIRE_NO;

	/**
	 * Constant that indicates autowiring bean properties by name.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_BY_NAME = AutowireCapableBeanFactory.AUTOWIRE_BY_NAME;

	/**
	 * Constant that indicates autowiring bean properties by type.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_BY_TYPE = AutowireCapableBeanFactory.AUTOWIRE_BY_TYPE;

	/**
	 * Constant that indicates autowiring a constructor.
	 * @see #setAutowireMode
	 */
	public static final int AUTOWIRE_CONSTRUCTOR = AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR;

	/**
	 * Constant that indicates determining an appropriate autowire strategy
	 * through introspection of the bean class.
	 * @see #setAutowireMode
	 * @deprecated as of Spring 3.0: If you are using mixed autowiring strategies,
	 * use annotation-based autowiring for clearer demarcation of autowiring needs.
	 */
	@Deprecated
	public static final int AUTOWIRE_AUTODETECT = AutowireCapableBeanFactory.AUTOWIRE_AUTODETECT;

	/**
	 * Constant that indicates no dependency check at all.
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_NONE = 0;

	/**
	 * Constant that indicates dependency checking for object references.
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_OBJECTS = 1;

	/**
	 * Constant that indicates dependency checking for "simple" properties.
	 * @see #setDependencyCheck
	 * @see org.springframework.beans.BeanUtils#isSimpleProperty
	 */
	public static final int DEPENDENCY_CHECK_SIMPLE = 2;

	/**
	 * Constant that indicates dependency checking for all properties
	 * (object references as well as "simple" properties).
	 * @see #setDependencyCheck
	 */
	public static final int DEPENDENCY_CHECK_ALL = 3;

	/**
	 * Constant that indicates the container should attempt to infer the
	 * {@link #setDestroyMethodName destroy method name} for a bean as opposed to
	 * explicit specification of a method name. The value {@value} is specifically
	 * designed to include characters otherwise illegal in a method name, ensuring
	 * no possibility of collisions with legitimately named methods having the same
	 * name.
	 * <p>Currently, the method names detected during destroy method inference
	 * are "close" and "shutdown", if present on the specific bean class.
	 */
	public static final String INFER_METHOD = "(inferred)";

	private volatile Object beanClass;

	private String scope = SCOPE_DEFAULT;

	private boolean abstractFlag = false;
    //是否延迟加载，对应bean属性lazy-init
	private boolean lazyInit = false;
    //自动注入模式，对应bean属性autowire
	private int autowireMode = AUTOWIRE_NO;
    //依赖检查
	private int dependencyCheck = DEPENDENCY_CHECK_NONE;
    //用来表示一个bean的实例化依靠另一个bean先实例化，对应bean属性的depend-on
	private String[] dependsOn;
    //autowire-candicate属性设置为false，这样容器在查找自动装配对象时将不考虑bean,则它不会被考虑作为其他bean自动装配的候选者，但是该bean本身还是可以使用自动装配来注入其他bean的
	//对应bean属性的autowire-candidate
	private boolean autowireCandidate = true;
    //自动装配时当出现多个bean候选者时，将作为首选者，对应bean属性primary
	private boolean primary = false;
   //用于记录Qualifier,对应子元素qualifier
	private final Map<String, AutowireCandidateQualifier> qualifiers =
			new LinkedHashMap<String, AutowireCandidateQualifier>(0);
   //允许访问非公开的构造器和方法，程序设置
	private boolean nonPublicAccessAllowed = true;
   //是否以一种宽松的模式解析构造函数，默认为true
	private boolean lenientConstructorResolution = true;
    //对应bean属性的factory-bean
	private String factoryBeanName;
    //对应bean属性的factory-method
	private String factoryMethodName;
   //记录构造函数注入属性，对应bean属性constructor-arg
	private ConstructorArgumentValues constructorArgumentValues;
   //普通属性集合
	private MutablePropertyValues propertyValues;
   //方法重写的持有者，记录lookup-method  replaced-method元素
	private MethodOverrides methodOverrides = new MethodOverrides();
    //初始化方法，对应bean属性的init-method
	private String initMethodName;
    //销毁方法，对应bean属性的deatory-method
	private String destroyMethodName;
    //是否执行init-method程序设置
	private boolean enforceInitMethod = true;
    //是否执行deatory-method程序设置
	private boolean enforceDestroyMethod = true;
    //是否是用户定义的而不是应用程序本身定义的，创建AOP时候为true，程序设置
	private boolean synthetic = false;
    //定义这个bean的应用，APPLICATION:用户；INFRASTRUCTURE:完全内部使用，与用户无关，SUPPORT：某些复杂配置的一部分
	private int role = BeanDefinition.ROLE_APPLICATION;
    //bean的描述信息
	private String description;
    //bean定义的资源
	private Resource resource;