//DefaultBeanDefinitionDocumentReader.java
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
		// 解析xml元素 
		BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
		if (bdHolder != null) {
			// 装饰
			bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
			try {
				// Register the final decorated instance.
				// 注册到容器中
				BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
			}
			catch (BeanDefinitionStoreException ex) {
				getReaderContext().error("Failed to register bean definition with name '" +
						bdHolder.getBeanName() + "'", ele, ex);
			}
			// Send registration event.
			// 发送事件
			getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
		}
	}

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder originalDef) {
		return decorateBeanDefinitionIfRequired(ele, originalDef, null);
	}

	/**
	 * Decorate the given bean definition through a namespace handler, if applicable.
	 * @param ele the current element
	 * @param originalDef the current bean definition
	 * @param containingBd the containing bean definition (if any)
	 * @return the decorated bean definition
	 */
	public BeanDefinitionHolder decorateBeanDefinitionIfRequired(
			Element ele, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {

		BeanDefinitionHolder finalDefinition = originalDef;
		// 遍历节点,寻找可以装饰的属性
		// Decorate based on custom attributes first.
		NamedNodeMap attributes = ele.getAttributes();
		for (int i = 0; i < attributes.getLength(); i++) {
			Node node = attributes.item(i);
			finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
		}
		// 遍历子节点,寻找可以装饰的子节点
		// Decorate based on custom nested elements.
		NodeList children = ele.getChildNodes();
		for (int i = 0; i < children.getLength(); i++) {
			Node node = children.item(i);
			if (node.getNodeType() == Node.ELEMENT_NODE) {
				finalDefinition = decorateIfRequired(node, finalDefinition, containingBd);
			}
		}
		return finalDefinition;
	}

public BeanDefinitionHolder decorateIfRequired(
			Node node, BeanDefinitionHolder originalDef, @Nullable BeanDefinition containingBd) {
		// 获取名称空间URI
		String namespaceUri = getNamespaceURI(node);
		// 判断是否是自定义名称空间,只对自定义名称空间进行处理
		if (namespaceUri != null && !isDefaultNamespace(namespaceUri)) {
			// 获取名称空间对应的处理器
			NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
			if (handler != null) {
				// 进行装饰处理
				BeanDefinitionHolder decorated =
						handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
				if (decorated != null) {
					return decorated;
				}
			}
			else if (namespaceUri.startsWith("http://www.springframework.org/schema/")) {
				error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
			}
			else {
				// A custom namespace, not to be handled by Spring - maybe "xml:...".
				if (logger.isDebugEnabled()) {
					logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
				}
			}
		}
		return originalDef;
	}

/*
 * Copyright 2002-2019 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.xml.support;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.w3c.dom.Attr;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.InputSource;

import org.springframework.aop.Advisor;
import org.springframework.aop.config.AbstractInterceptorDrivenBeanDefinitionDecorator;
import org.springframework.aop.framework.Advised;
import org.springframework.aop.interceptor.DebugInterceptor;
import org.springframework.aop.support.AopUtils;
import org.springframework.beans.BeanInstantiationException;
import org.springframework.beans.MutablePropertyValues;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.support.AbstractBeanDefinition;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.beans.factory.xml.AbstractSingleBeanDefinitionParser;
import org.springframework.beans.factory.xml.BeanDefinitionDecorator;
import org.springframework.beans.factory.xml.BeanDefinitionParser;
import org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver;
import org.springframework.beans.factory.xml.NamespaceHandlerResolver;
import org.springframework.beans.factory.xml.NamespaceHandlerSupport;
import org.springframework.beans.factory.xml.ParserContext;
import org.springframework.beans.factory.xml.PluggableSchemaResolver;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.context.ApplicationListener;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.Resource;
import org.springframework.tests.aop.interceptor.NopInterceptor;
import org.springframework.tests.sample.beans.ITestBean;
import org.springframework.tests.sample.beans.TestBean;

import static java.lang.String.format;
import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatExceptionOfType;

/**
 * Unit tests for custom XML namespace handler implementations.
 *
 * @author Rob Harrop
 * @author Rick Evans
 * @author Chris Beams
 * @author Juergen Hoeller
 */
public class CustomNamespaceHandlerTests {

	private static final Class<?> CLASS = CustomNamespaceHandlerTests.class;
	private static final String CLASSNAME = CLASS.getSimpleName();
	private static final String FQ_PATH = "org/springframework/beans/factory/xml/support";

	private static final String NS_PROPS = format("%s/%s.properties", FQ_PATH, CLASSNAME);
	private static final String NS_XML = format("%s/%s-context.xml", FQ_PATH, CLASSNAME);
	private static final String TEST_XSD = format("%s/%s.xsd", FQ_PATH, CLASSNAME);

	private GenericApplicationContext beanFactory;


	@BeforeEach
	public void setUp() throws Exception {
		NamespaceHandlerResolver resolver = new DefaultNamespaceHandlerResolver(CLASS.getClassLoader(), NS_PROPS);
		this.beanFactory = new GenericApplicationContext();
		XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this.beanFactory);
		reader.setNamespaceHandlerResolver(resolver);
		reader.setValidationMode(XmlBeanDefinitionReader.VALIDATION_XSD);
		reader.setEntityResolver(new DummySchemaResolver());
		reader.loadBeanDefinitions(getResource());
		this.beanFactory.refresh();
	}


	@Test
	public void testSimpleParser() throws Exception {
		TestBean bean = (TestBean) this.beanFactory.getBean("testBean");
		assertTestBean(bean);
	}

	@Test
	public void testSimpleDecorator() throws Exception {
		TestBean bean = (TestBean) this.beanFactory.getBean("customisedTestBean");
		assertTestBean(bean);
	}

	@Test
	public void testProxyingDecorator() throws Exception {
		ITestBean bean = (ITestBean) this.beanFactory.getBean("debuggingTestBean");
		assertTestBean(bean);
		assertThat(AopUtils.isAopProxy(bean)).isTrue();
		Advisor[] advisors = ((Advised) bean).getAdvisors();
		assertThat(advisors.length).as("Incorrect number of advisors").isEqualTo(1);
		assertThat(advisors[0].getAdvice().getClass()).as("Incorrect advice class").isEqualTo(DebugInterceptor.class);
	}

	@Test
	public void testProxyingDecoratorNoInstance() throws Exception {
		String[] beanNames = this.beanFactory.getBeanNamesForType(ApplicationListener.class);
		assertThat(Arrays.asList(beanNames).contains("debuggingTestBeanNoInstance")).isTrue();
		assertThat(this.beanFactory.getType("debuggingTestBeanNoInstance")).isEqualTo(ApplicationListener.class);
		assertThatExceptionOfType(BeanCreationException.class).isThrownBy(() ->
				this.beanFactory.getBean("debuggingTestBeanNoInstance"))
			.satisfies(ex -> assertThat(ex.getRootCause()).isInstanceOf(BeanInstantiationException.class));
	}

	@Test
	public void testChainedDecorators() throws Exception {
		ITestBean bean = (ITestBean) this.beanFactory.getBean("chainedTestBean");
		assertTestBean(bean);
		assertThat(AopUtils.isAopProxy(bean)).isTrue();
		Advisor[] advisors = ((Advised) bean).getAdvisors();
		assertThat(advisors.length).as("Incorrect number of advisors").isEqualTo(2);
		assertThat(advisors[0].getAdvice().getClass()).as("Incorrect advice class").isEqualTo(DebugInterceptor.class);
		assertThat(advisors[1].getAdvice().getClass()).as("Incorrect advice class").isEqualTo(NopInterceptor.class);
	}

	@Test
	public void testDecorationViaAttribute() throws Exception {
		BeanDefinition beanDefinition = this.beanFactory.getBeanDefinition("decorateWithAttribute");
		assertThat(beanDefinition.getAttribute("objectName")).isEqualTo("foo");
	}

	@Test  // SPR-2728
	public void testCustomElementNestedWithinUtilList() throws Exception {
		List<?> things = (List<?>) this.beanFactory.getBean("list.of.things");
		assertThat(things).isNotNull();
		assertThat(things.size()).isEqualTo(2);
	}

	@Test  // SPR-2728
	public void testCustomElementNestedWithinUtilSet() throws Exception {
		Set<?> things = (Set<?>) this.beanFactory.getBean("set.of.things");
		assertThat(things).isNotNull();
		assertThat(things.size()).isEqualTo(2);
	}

	@Test  // SPR-2728
	public void testCustomElementNestedWithinUtilMap() throws Exception {
		Map<?, ?> things = (Map<?, ?>) this.beanFactory.getBean("map.of.things");
		assertThat(things).isNotNull();
		assertThat(things.size()).isEqualTo(2);
	}


	private void assertTestBean(ITestBean bean) {
		assertThat(bean.getName()).as("Invalid name").isEqualTo("Rob Harrop");
		assertThat(bean.getAge()).as("Invalid age").isEqualTo(23);
	}

	private Resource getResource() {
		return new ClassPathResource(NS_XML);
	}


	private final class DummySchemaResolver extends PluggableSchemaResolver {

		public DummySchemaResolver() {
			super(CLASS.getClassLoader());
		}

		@Override
		public InputSource resolveEntity(String publicId, String systemId) throws IOException {
			InputSource source = super.resolveEntity(publicId, systemId);
			if (source == null) {
				Resource resource = new ClassPathResource(TEST_XSD);
				source = new InputSource(resource.getInputStream());
				source.setPublicId(publicId);
				source.setSystemId(systemId);
			}
			return source;
		}
	}

}


/**
 * Custom namespace handler implementation.
 *	自定义名称空间处理器
 * @author Rob Harrop
 */
final class TestNamespaceHandler extends NamespaceHandlerSupport {

	@Override
	public void init() {
    // 注册节点为 testBean 的解析器
		registerBeanDefinitionParser("testBean", new TestBeanDefinitionParser());
    // 注册节点为 person 的解析器
		registerBeanDefinitionParser("person", new PersonDefinitionParser());
		
    // 注册 set 装饰器
		registerBeanDefinitionDecorator("set", new PropertyModifyingBeanDefinitionDecorator());
    // 注册 debug 装饰器
		registerBeanDefinitionDecorator("debug", new DebugBeanDefinitionDecorator());
    // 注册 nop 装饰器
		registerBeanDefinitionDecorator("nop", new NopInterceptorBeanDefinitionDecorator());
    // 注册 属性为 object-name 的装饰器
		registerBeanDefinitionDecoratorForAttribute("object-name", new ObjectNameBeanDefinitionDecorator());
	}

	// 节点为 testBean 的解析器
	private static class TestBeanDefinitionParser implements BeanDefinitionParser {

		@Override
		public BeanDefinition parse(Element element, ParserContext parserContext) {
			RootBeanDefinition definition = new RootBeanDefinition();
			definition.setBeanClass(TestBean.class);

			MutablePropertyValues mpvs = new MutablePropertyValues();
			mpvs.add("name", element.getAttribute("name"));
			mpvs.add("age", element.getAttribute("age"));
			definition.setPropertyValues(mpvs);

			parserContext.getRegistry().registerBeanDefinition(element.getAttribute("id"), definition);
			return null;
		}
	}

	// 节点为 person 的解析器
	private static final class PersonDefinitionParser extends AbstractSingleBeanDefinitionParser {

		@Override
		protected Class<?> getBeanClass(Element element) {
			return TestBean.class;
		}

		@Override
		protected void doParse(Element element, BeanDefinitionBuilder builder) {
			builder.addPropertyValue("name", element.getAttribute("name"));
			builder.addPropertyValue("age", element.getAttribute("age"));
		}
	}

	// set 装饰器
	private static class PropertyModifyingBeanDefinitionDecorator implements BeanDefinitionDecorator {

		@Override
		public BeanDefinitionHolder decorate(Node node, BeanDefinitionHolder definition, ParserContext parserContext) {
			Element element = (Element) node;
			BeanDefinition def = definition.getBeanDefinition();

			MutablePropertyValues mpvs = (def.getPropertyValues() == null) ? new MutablePropertyValues() : def.getPropertyValues();
			mpvs.add("name", element.getAttribute("name"));
			mpvs.add("age", element.getAttribute("age"));

			((AbstractBeanDefinition) def).setPropertyValues(mpvs);
			return definition;
		}
	}

	// debug 装饰器
	private static class DebugBeanDefinitionDecorator extends AbstractInterceptorDrivenBeanDefinitionDecorator {

		@Override
		protected BeanDefinition createInterceptorDefinition(Node node) {
			return new RootBeanDefinition(DebugInterceptor.class);
		}
	}

	// nop 装饰器
	private static class NopInterceptorBeanDefinitionDecorator extends AbstractInterceptorDrivenBeanDefinitionDecorator {

		@Override
		protected BeanDefinition createInterceptorDefinition(Node node) {
			return new RootBeanDefinition(NopInterceptor.class);
		}
	}

	// 属性为 object-name 的装饰器
	private static class ObjectNameBeanDefinitionDecorator implements BeanDefinitionDecorator {

		@Override
		public BeanDefinitionHolder decorate(Node node, BeanDefinitionHolder definition, ParserContext parserContext) {
			Attr objectNameAttribute = (Attr) node;
			definition.getBeanDefinition().setAttribute("objectName", objectNameAttribute.getValue());
			return definition;
		}
	}

}