org.springframework.beans.factory.xml

## 接口 NamespaceHandler

- 所有已知实现类:
    NamespaceHandlerSupport, SimpleConstructorNamespaceHandler, SimplePropertyNamespaceHandler, UtilNamespaceHandler

      public interface NamespaceHandler

  Base interface used by the `DefaultBeanDefinitionDocumentReader` for handling custom namespaces in a Spring XML configuration file.

  Implementations are expected to return implementations of the `BeanDefinitionParser` interface for custom top-level tags and implementations of the `BeanDefinitionDecorator` interface for custom nested tags.

  The parser will call `parse(org.w3c.dom.Element, org.springframework.beans.factory.xml.ParserContext)` when it encounters a custom tag directly under the `<beans>` tags and `decorate(org.w3c.dom.Node, org.springframework.beans.factory.config.BeanDefinitionHolder, org.springframework.beans.factory.xml.ParserContext)` when it encounters a custom tag directly under a `<bean>` tag.

  Developers writing their own custom element extensions typically will not implement this interface directly, but rather make use of the provided `NamespaceHandlerSupport` class.

  从以下版本开始:
    2.0
  作者:
    Rob Harrop, Erik Wiersma
  另请参阅:
    `DefaultBeanDefinitionDocumentReader`, `NamespaceHandlerResolver`

- - ### 方法概要

    所有方法 实例方法 抽象方法
    限定符和类型 | 方法和说明
    --- | ---
    `BeanDefinitionHolder` | `decorate(Node source, BeanDefinitionHolder definition, ParserContext parserContext)` Parse the specified `Node` and decorate the supplied `BeanDefinitionHolder`, returning the decorated definition.
    `void` | `init()` Invoked by the `DefaultBeanDefinitionDocumentReader` after construction but before any custom elements are parsed.
    `BeanDefinition` | `parse(Element element, ParserContext parserContext)` Parse the specified `Element` and register any resulting `BeanDefinitions` with the `BeanDefinitionRegistry` that is embedded in the supplied `ParserContext`.

- - ### 方法详细资料

    - #### init

          void init()

      Invoked by the `DefaultBeanDefinitionDocumentReader` after construction but before any custom elements are parsed.
      另请参阅:
        `NamespaceHandlerSupport.registerBeanDefinitionParser(String, BeanDefinitionParser)`

    - #### parse

          @Nullable
          BeanDefinition parse(Element element,
                                          ParserContext parserContext)

      Parse the specified `Element` and register any resulting `BeanDefinitions` with the `BeanDefinitionRegistry` that is embedded in the supplied `ParserContext`.

      Implementations should return the primary `BeanDefinition` that results from the parse phase if they wish to be used nested inside (for example) a `<property>` tag.

      Implementations may return `null` if they will not be used in a nested scenario.

      参数:
        `element` - the element that is to be parsed into one or more `BeanDefinitions`
        `parserContext` - the object encapsulating the current state of the parsing process
      返回:
        the primary `BeanDefinition` (can be `null` as explained above)

    - #### decorate

          @Nullable
          BeanDefinitionHolder decorate(Node source,
                                                   BeanDefinitionHolder definition,
                                                   ParserContext parserContext)

      Parse the specified `Node` and decorate the supplied `BeanDefinitionHolder`, returning the decorated definition.

      The `Node` may be either an `Attr` or an `Element`, depending on whether a custom attribute or element is being parsed.

      Implementations may choose to return a completely new definition, which will replace the original definition in the resulting `BeanFactory`.

      The supplied `ParserContext` can be used to register any additional beans needed to support the main definition.

      参数:
        `source` - the source element or attribute that is to be parsed
        `definition` - the current bean definition
        `parserContext` - the object encapsulating the current state of the parsing process
      返回:
        the decorated definition (to be registered in the BeanFactory), or simply the original bean definition if no decoration is required. A `null` value is strictly speaking invalid, but will be leniently treated like the case where the original bean definition gets returned.