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类全路径: org.springframework.beans.factory.xml.NamespaceHandlerSupport
首先阅读NamespaceHandlerSupport中的成员变量
NamespaceHandlerSupport 成员变量有3个.
parsers
存储 XML 中 Element 和 BeanDefinitionParser 的对应关系
decorators
存储 XML 中 Element 和 BeanDefinitionDecorator 的对应关系
attributeDecorators
存储 XML 中 Attr 和 BeanDefinitionDecorator 的对应关系
public abstract class NamespaceHandlerSupport implements NamespaceHandler {
/**
* Stores the {@link BeanDefinitionParser} implementations keyed by the
* local name of the {@link Element Elements} they handle.
*
* key: xml elementName
* value: BeanDefinitionParser
*/
private final Map<String, BeanDefinitionParser> parsers = new HashMap<>();
/**
* Stores the {@link BeanDefinitionDecorator} implementations keyed by the
* local name of the {@link Element Elements} they handle.
*
* key: xml elementName
* value: BeanDefinitionDecorator
*/
private final Map<String, BeanDefinitionDecorator> decorators = new HashMap<>();
/**
* Stores the {@link BeanDefinitionDecorator} implementations keyed by the local
* name of the {@link Attr Attrs} they handle.
*
* 存储有关 {@link Attr} 的 BeanDefinitionDecorator 容器
*
* key: attr
* value: BeanDefinitionDecorator
*/
private final Map<String, BeanDefinitionDecorator> attributeDecorators = new HashMap<>();
}
这些成员变量很重要. 在Spring中自定义标签的解析就需要依赖它们. 下面举几个例子
Aop
@Override
public void init() {
// In 2.0 XSD as well as in 2.1 XSD.
registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
// Spring AOP 解析
registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());
// Only in 2.0 XSD: moved to context namespace as of 2.1
registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
}
Jdbc
@Override
public void init() {
registerBeanDefinitionParser("embedded-database", new EmbeddedDatabaseBeanDefinitionParser());
registerBeanDefinitionParser("initialize-database", new InitializeDatabaseBeanDefinitionParser());
}
tx
@Override
public void init() {
// 切面解析
registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
// 注解驱动
registerBeanDefinitionParser("annotation-driven",
new AnnotationDrivenBeanDefinitionParser());
registerBeanDefinitionParser("jta-transaction-manager",
new JtaTransactionManagerBeanDefinitionParser());
}
NamespaceHandlerSupport 的子类都会将自己需要的BeanDefinitionParser和BeanDefinitionDecorator注册(添加)到对应的容器中.
下面我们对注册(registerBeanDefinitionParser)等方法进行分析
map#putorg.springframework.beans.factory.xml.NamespaceHandlerSupport#registerBeanDefinitionParserprotected final void registerBeanDefinitionParser(String elementName, BeanDefinitionParser parser) {
this.parsers.put(elementName, parser);
}
org.springframework.beans.factory.xml.NamespaceHandlerSupport#registerBeanDefinitionDecoratorprotected final void registerBeanDefinitionDecorator(String elementName, BeanDefinitionDecorator dec) {
this.decorators.put(elementName, dec);
}
org.springframework.beans.factory.xml.NamespaceHandlerSupport#registerBeanDefinitionDecoratorForAttributeprotected final void registerBeanDefinitionDecoratorForAttribute(String attrName, BeanDefinitionDecorator dec) {
this.attributeDecorators.put(attrName, dec);
}
在了解注册方法后我们来看NamespaceHandler的实现方法
方法签名: org.springframework.beans.factory.xml.NamespaceHandlerSupport#parse
方法流程
@Override
@Nullable
public BeanDefinition parse(Element element, ParserContext parserContext) {
// 搜索 element 对应的 BeanDefinitionParser
BeanDefinitionParser parser = findParserForElement(element, parserContext);
// 解析
return (parser != null ? parser.parse(element, parserContext) : null);
}
BeanDefinitionParser的方法方法签名: org.springframework.beans.factory.xml.NamespaceHandlerSupport#findParserForElement
寻找过程
通过 Element 的名称直接从容器中获取
@Nullable
private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
// 获取 element 的名称
String localName = parserContext.getDelegate().getLocalName(element);
// 从容器中获取
BeanDefinitionParser parser = this.parsers.get(localName);
if (parser == null) {
parserContext.getReaderContext().fatal(
"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
}
return parser;
}
org.springframework.beans.factory.xml.NamespaceHandlerSupport#decorate@Override
@Nullable
public BeanDefinitionHolder decorate(
Node node, BeanDefinitionHolder definition, ParserContext parserContext) {
// 根据 node 获取 BeanDefinitionDecorator
BeanDefinitionDecorator decorator = findDecoratorForNode(node, parserContext);
// 解析
return (decorator != null ? decorator.decorate(node, definition, parserContext) : null);
}
findDecoratorForNode 的流程对于BeanDefinitionDecorator 在前文已经提到存储的容器有2个
decorators
存储key类型是 element
attributeDecorators
存储key类型是 Attr
根据上述两点我们大致可以推算出搜索方法.
org.springframework.beans.factory.xml.NamespaceHandlerSupport#findDecoratorForNode@Nullable
private BeanDefinitionDecorator findDecoratorForNode(Node node, ParserContext parserContext) {
BeanDefinitionDecorator decorator = null;
String localName = parserContext.getDelegate().getLocalName(node);
if (node instanceof Element) {
decorator = this.decorators.get(localName);
}
else if (node instanceof Attr) {
decorator = this.attributeDecorators.get(localName);
}
else {
parserContext.getReaderContext().fatal(
"Cannot decorate based on Nodes of type [" + node.getClass().getName() + "]", node);
}
if (decorator == null) {
parserContext.getReaderContext().fatal("Cannot locate BeanDefinitionDecorator for " +
(node instanceof Element ? "element" : "attribute") + " [" + localName + "]", node);
}
return decorator;
}
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