Spring解密 - 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;
	}


}