spring BeanDefinition接口定义研究

BeanDefinition接口包括了一些基本属性的设置，它继承了AttributeAccessor与BeanMetadataElement。
AttributeAccessor：用来管理属性
/**
* Set the attribute defined by {@code name} to the supplied {@code value}.
* If {@code value} is {@code null}, the attribute is {@link #removeAttribute removed}.
* <p>In general, users should take care to prevent overlaps with other
* metadata attributes by using fully-qualified names, perhaps using
* class or package names as prefix.
* @param name the unique attribute key
* @param value the attribute value to be attached
*/
void setAttribute(String name, Object value);

/**
* Get the value of the attribute identified by {@code name}.
* Return {@code null} if the attribute doesn't exist.
* @param name the unique attribute key
* @return the current value of the attribute, if any
*/
Object getAttribute(String name);

/**
* Remove the attribute identified by {@code name} and return its value.
* Return {@code null} if no attribute under {@code name} is found.
* @param name the unique attribute key
* @return the last value of the attribute, if any
*/
Object removeAttribute(String name);

/**
* Return {@code true} if the attribute identified by {@code name} exists.
* Otherwise return {@code false}.
* @param name the unique attribute key
*/
boolean hasAttribute(String name);

/**
* Return the names of all attributes.
*/
String[] attributeNames();
BeanMetadataElement：加载一些配置文件（.properties等例如mysql的基本配置）
/**
* Return the configuration source {@code Object} for this metadata element
* (may be {@code null}).
*/
Object getSource();