Spring源码解密之自定义标签与解析

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns="http://www.battcn.com/schema/battcn" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:beans="http://www.springframework.org/schema/beans" targetNamespace="http://www.battcn.com/schema/battcn"
 elementFormDefault="qualified"
 attributeFormDefault="unqualified">
 <xsd:import namespace="http://www.springframework.org/schema/beans" />
 <xsd:element name="application">
 <xsd:complexType>
 <xsd:complexContent>
 <xsd:extension base="beans:identifiedType">
  <xsd:attribute name="name" type="xsd:string" use="required"/>
 </xsd:extension>
 </xsd:complexContent>
 </xsd:complexType>
 </xsd:element>
</xsd:schema>

public class ApplicationBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {
 @Override
 protected Class getBeanClass(Element element) {
 // 接收对象的类型 如：String name = (String) context.getBean("battcn");
 return String.class;
 }
 @Override
 protected void doParse(Element element, BeanDefinitionBuilder bean) {
 // 在 xsd 中定义的 name 属性
 String name = element.getAttribute("name");
 bean.addConstructorArgValue(name);
 }
}

public class BattcnNamespaceHandler extends NamespaceHandlerSupport {
 @Override
 public void init() {
 registerBeanDefinitionParser("application", new ApplicationBeanDefinitionParser());
 }
}

http\://www.battcn.com/schema/battcn=com.battcn.handler.BattcnNamespaceHandler

http\://www.battcn.com/schema/battcn.xsd=battcn.xsd

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:battcn="http://www.battcn.com/schema/battcn" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
 http://www.battcn.com/schema/battcn
 http://www.battcn.com/schema/battcn.xsd">
 <battcn:application id="battcn" name="Levin"/>
</beans>

public class Application {
 public static void main(String[] args) {
 ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
 String name = (String) context.getBean("battcn");
 System.out.println(name);
 }
}

public class BeanDefinitionParserDelegate {
 @Nullable
 public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) {
 // 获取命名空间地址 http://www.battcn.com/schema/battcn
 String namespaceUri = getNamespaceURI(ele);
 if (namespaceUri == null) {
 return null;
 }
 // NamespaceHandler 就是 自定义的 BattcnNamespaceHandler 中注册的 application
 NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
 if (handler == null) {
 error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
 return null;
 }
 return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
 }
}

public class XmlBeanDefinitionReader {
 public NamespaceHandlerResolver getNamespaceHandlerResolver() {
 if (this.namespaceHandlerResolver == null) {
 this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
 }
 return this.namespaceHandlerResolver;
 }
}

public class DefaultNamespaceHandlerResolver {
 @Override
 @Nullable
 public NamespaceHandler resolve(String namespaceUri) {
 Map<String, Object> handlerMappings = getHandlerMappings();
 // 从 handlerMappings 提取 handlerOrClassName
 Object handlerOrClassName = handlerMappings.get(namespaceUri);
 if (handlerOrClassName == null) {
 return null;
 }
 else if (handlerOrClassName instanceof NamespaceHandler) {
 return (NamespaceHandler) handlerOrClassName;
 }
 else {
 String className = (String) handlerOrClassName;
 try {
 Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
 if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
 throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
 "] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
 }
 // 根据命名空间寻找对应的信息
 NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
 // Handler 初始化
 namespaceHandler.init();
 handlerMappings.put(namespaceUri, namespaceHandler);
 return namespaceHandler;
 }
 catch (ClassNotFoundException ex) {
 throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
 namespaceUri + "] not found", ex);
 }
 catch (LinkageError err) {
 throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
 namespaceUri + "]: problem with handler class file or dependent class", err);
 }
 }
 }
}

public class NamespaceHandlerSupport {
 @Override
 @Nullable
 public BeanDefinition parse(Element element, ParserContext parserContext) {
 BeanDefinitionParser parser = findParserForElement(element, parserContext);
 return (parser != null ? parser.parse(element, parserContext) : null);
 }
 @Nullable
 private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
 // 解析出 <battcn:application /> 中的 application
 String localName = parserContext.getDelegate().getLocalName(element);
 BeanDefinitionParser parser = this.parsers.get(localName);
 if (parser == null) {
 parserContext.getReaderContext().fatal(
 "Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
 }
 return parser;
 }
}