XmlBeanDefinitionReader.java

/*
 * Copyright 2002-2021 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;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashSet;
import java.util.Set;

import javax.xml.parsers.ParserConfigurationException;

import org.w3c.dom.Document;
import org.xml.sax.EntityResolver;
import org.xml.sax.ErrorHandler;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.SAXParseException;

import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.parsing.EmptyReaderEventListener;
import org.springframework.beans.factory.parsing.FailFastProblemReporter;
import org.springframework.beans.factory.parsing.NullSourceExtractor;
import org.springframework.beans.factory.parsing.ProblemReporter;
import org.springframework.beans.factory.parsing.ReaderEventListener;
import org.springframework.beans.factory.parsing.SourceExtractor;
import org.springframework.beans.factory.support.AbstractBeanDefinitionReader;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.core.Constants;
import org.springframework.core.NamedThreadLocal;
import org.springframework.core.io.DescriptiveResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.xml.SimpleSaxErrorHandler;
import org.springframework.util.xml.XmlValidationModeDetector;

/**
 * Bean definition reader for XML bean definitions.
 * Delegates the actual XML document reading to an implementation
 * of the {@link BeanDefinitionDocumentReader} interface.
 *
 * <p>Typically applied to a
 * {@link org.springframework.beans.factory.support.DefaultListableBeanFactory}
 * or a {@link org.springframework.context.support.GenericApplicationContext}.
 *
 * <p>This class loads a DOM document and applies the BeanDefinitionDocumentReader to it.
 * The document reader will register each bean definition with the given bean factory,
 * talking to the latter's implementation of the
 * {@link org.springframework.beans.factory.support.BeanDefinitionRegistry} interface.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @author Chris Beams
 * @since 26.11.2003
 * @see #setDocumentReaderClass
 * @see BeanDefinitionDocumentReader
 * @see DefaultBeanDefinitionDocumentReader
 * @see BeanDefinitionRegistry
 * @see org.springframework.beans.factory.support.DefaultListableBeanFactory
 * @see org.springframework.context.support.GenericApplicationContext
 */
public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader {

	/**
	 * Indicates that the validation should be disabled.
	 */
	public static final int VALIDATION_NONE = XmlValidationModeDetector.VALIDATION_NONE;

	/**
	 * Indicates that the validation mode should be detected automatically.
	 */
	public static final int VALIDATION_AUTO = XmlValidationModeDetector.VALIDATION_AUTO;

	/**
	 * Indicates that DTD validation should be used.
	 */
	public static final int VALIDATION_DTD = XmlValidationModeDetector.VALIDATION_DTD;

	/**
	 * Indicates that XSD validation should be used.
	 */
	public static final int VALIDATION_XSD = XmlValidationModeDetector.VALIDATION_XSD;


	/** Constants instance for this class. */
	private static final Constants constants = new Constants(XmlBeanDefinitionReader.class);

	private int validationMode = VALIDATION_AUTO;

	private boolean namespaceAware = false;

	private Class<? extends BeanDefinitionDocumentReader> documentReaderClass =
			DefaultBeanDefinitionDocumentReader.class;

	private ProblemReporter problemReporter = new FailFastProblemReporter();

	private ReaderEventListener eventListener = new EmptyReaderEventListener();

	private SourceExtractor sourceExtractor = new NullSourceExtractor();

	@Nullable
	private NamespaceHandlerResolver namespaceHandlerResolver;

	private DocumentLoader documentLoader = new DefaultDocumentLoader();

	@Nullable
	private EntityResolver entityResolver;

	private ErrorHandler errorHandler = new SimpleSaxErrorHandler(logger);

	private final XmlValidationModeDetector validationModeDetector = new XmlValidationModeDetector();

	private final ThreadLocal<Set<EncodedResource>> resourcesCurrentlyBeingLoaded =
			new NamedThreadLocal<>("XML bean definition resources currently being loaded"){
				@Override
				protected Set<EncodedResource> initialValue() {
					return new HashSet<>(4);
				}
			};


	/**
	 * Create new XmlBeanDefinitionReader for the given bean factory.
	 * @param registry the BeanFactory to load bean definitions into,
	 * in the form of a BeanDefinitionRegistry
	 */
	public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {
		super(registry);
	}


	/**
	 * Set whether to use XML validation. Default is {@code true}.
	 * <p>This method switches namespace awareness on if validation is turned off,
	 * in order to still process schema namespaces properly in such a scenario.
	 * @see #setValidationMode
	 * @see #setNamespaceAware
	 */
	public void setValidating(boolean validating) {
		this.validationMode = (validating ? VALIDATION_AUTO : VALIDATION_NONE);
		this.namespaceAware = !validating;
	}

	/**
	 * Set the validation mode to use by name. Defaults to {@link #VALIDATION_AUTO}.
	 * @see #setValidationMode
	 */
	public void setValidationModeName(String validationModeName) {
		setValidationMode(constants.asNumber(validationModeName).intValue());
	}

	/**
	 * Set the validation mode to use. Defaults to {@link #VALIDATION_AUTO}.
	 * <p>Note that this only activates or deactivates validation itself.
	 * If you are switching validation off for schema files, you might need to
	 * activate schema namespace support explicitly: see {@link #setNamespaceAware}.
	 *
	 * 设置要使用的验证模式。默认为 VALIDATION_AUTO。
	 * 请注意，这只会激活或停用验证本身。如果要关闭模式文件的验证，则可能需要显式激活模式命名空间支持
	 */
	public void setValidationMode(int validationMode) {
		this.validationMode = validationMode;
	}

	/**
	 * Return the validation mode to use.
	 */
	public int getValidationMode() {
		return this.validationMode;
	}

	/**
	 * Set whether or not the XML parser should be XML namespace aware.
	 * Default is "false".
	 * <p>This is typically not needed when schema validation is active.
	 * However, without validation, this has to be switched to "true"
	 * in order to properly process schema namespaces.
	 */
	public void setNamespaceAware(boolean namespaceAware) {
		this.namespaceAware = namespaceAware;
	}

	/**
	 * Return whether or not the XML parser should be XML namespace aware.
	 */
	public boolean isNamespaceAware() {
		return this.namespaceAware;
	}

	/**
	 * Specify which {@link org.springframework.beans.factory.parsing.ProblemReporter} to use.
	 * <p>The default implementation is {@link org.springframework.beans.factory.parsing.FailFastProblemReporter}
	 * which exhibits fail fast behaviour. External tools can provide an alternative implementation
	 * that collates errors and warnings for display in the tool UI.
	 */
	public void setProblemReporter(@Nullable ProblemReporter problemReporter) {
		this.problemReporter = (problemReporter != null ? problemReporter : new FailFastProblemReporter());
	}

	/**
	 * Specify which {@link ReaderEventListener} to use.
	 * <p>The default implementation is EmptyReaderEventListener which discards every event notification.
	 * External tools can provide an alternative implementation to monitor the components being
	 * registered in the BeanFactory.
	 */
	public void setEventListener(@Nullable ReaderEventListener eventListener) {
		this.eventListener = (eventListener != null ? eventListener : new EmptyReaderEventListener());
	}

	/**
	 * Specify the {@link SourceExtractor} to use.
	 * <p>The default implementation is {@link NullSourceExtractor} which simply returns {@code null}
	 * as the source object. This means that - during normal runtime execution -
	 * no additional source metadata is attached to the bean configuration metadata.
	 */
	public void setSourceExtractor(@Nullable SourceExtractor sourceExtractor) {
		this.sourceExtractor = (sourceExtractor != null ? sourceExtractor : new NullSourceExtractor());
	}

	/**
	 * Specify the {@link NamespaceHandlerResolver} to use.
	 * <p>If none is specified, a default instance will be created through
	 * {@link #createDefaultNamespaceHandlerResolver()}.
	 */
	public void setNamespaceHandlerResolver(@Nullable NamespaceHandlerResolver namespaceHandlerResolver) {
		this.namespaceHandlerResolver = namespaceHandlerResolver;
	}

	/**
	 * Specify the {@link DocumentLoader} to use.
	 * <p>The default implementation is {@link DefaultDocumentLoader}
	 * which loads {@link Document} instances using JAXP.
	 */
	public void setDocumentLoader(@Nullable DocumentLoader documentLoader) {
		this.documentLoader = (documentLoader != null ? documentLoader : new DefaultDocumentLoader());
	}

	/**
	 * Set a SAX entity resolver to be used for parsing.
	 * <p>By default, {@link ResourceEntityResolver} will be used. Can be overridden
	 * for custom entity resolution, for example relative to some specific base path.
	 */
	public void setEntityResolver(@Nullable EntityResolver entityResolver) {
		this.entityResolver = entityResolver;
	}

	/**
	 * Return the EntityResolver to use, building a default resolver
	 * if none specified.
	 */
	protected EntityResolver getEntityResolver() {
		if (this.entityResolver == null) {
			// Determine default EntityResolver to use.
			ResourceLoader resourceLoader = getResourceLoader();
			if (resourceLoader != null) {
				this.entityResolver = new ResourceEntityResolver(resourceLoader);
			}
			else {
				this.entityResolver = new DelegatingEntityResolver(getBeanClassLoader());
			}
		}
		return this.entityResolver;
	}

	/**
	 * Set an implementation of the {@code org.xml.sax.ErrorHandler}
	 * interface for custom handling of XML parsing errors and warnings.
	 * <p>If not set, a default SimpleSaxErrorHandler is used that simply
	 * logs warnings using the logger instance of the view class,
	 * and rethrows errors to discontinue the XML transformation.
	 * @see SimpleSaxErrorHandler
	 */
	public void setErrorHandler(ErrorHandler errorHandler) {
		this.errorHandler = errorHandler;
	}

	/**
	 * Specify the {@link BeanDefinitionDocumentReader} implementation to use,
	 * responsible for the actual reading of the XML bean definition document.
	 * <p>The default is {@link DefaultBeanDefinitionDocumentReader}.
	 * @param documentReaderClass the desired BeanDefinitionDocumentReader implementation class
	 */
	public void setDocumentReaderClass(Class<? extends BeanDefinitionDocumentReader> documentReaderClass) {
		this.documentReaderClass = documentReaderClass;
	}


	/**
	 * Load bean definitions from the specified XML file.
	 * @param resource the resource descriptor for the XML file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 */
	@Override
	public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException {
		/**
		 * EncodedResource类主要是用于对资服文件的编码进行处理
		 */
		System.err.println("当前处理的xml为:" + resource.getFilename());
		System.err.println("根据当前xml的resource封装成解码的EncodedResource");
		return loadBeanDefinitions(new EncodedResource(resource));
	}

	/**
	 * Load bean definitions from the specified XML file.
	 * @param encodedResource the resource descriptor for the XML file,
	 * allowing to specify an encoding to use for parsing the file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 *
	 * 对 Resource 使用EncodedResource 类进行封装 其中EncodedResource类会对编码进行处理
	 */
	public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException {
		Assert.notNull(encodedResource, "EncodedResource must not be null");
		if (logger.isTraceEnabled()) {
			logger.trace("Loading XML bean definitions from " + encodedResource);
		}
        /** 通过属性来记录已经加载的资源*/
		Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();

		if (!currentResources.add(encodedResource)) {
			throw new BeanDefinitionStoreException(
					"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
		}
        /** 获取输入流。从Resourse中获取对应的InputStream并构造InputSource
		 *  从encodedResource中获取已经封装的Resource对象并再次从Resource中获取其中的InputStream
		 */
		try (InputStream inputStream = encodedResource.getResource().getInputStream()) {
			InputSource inputSource = new InputSource(inputStream);
			if (encodedResource.getEncoding() != null) {
				inputSource.setEncoding(encodedResource.getEncoding());
			}
			/**
			 * 真正进入逻辑核心部分
			 * 通过构造的InputSource实例和Resource实例继续调用函数doLoadBeanDefinitions
			 */
			System.out.println("doLoadBeanDefinitions:\n " +
					"真正进入逻辑核心部分\n" +
					"通过构造的InputSource实例和Resource实例继续调用函数doLoadBeanDefinitions");
			return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"IOException parsing XML document from " + encodedResource.getResource(), ex);
		}
		finally {
			currentResources.remove(encodedResource);
			if (currentResources.isEmpty()) {
				this.resourcesCurrentlyBeingLoaded.remove();
			}
		}
	}

	/**
	 * Load bean definitions from the specified XML file.
	 * @param inputSource the SAX InputSource to read from
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(InputSource inputSource) throws BeanDefinitionStoreException {
		return loadBeanDefinitions(inputSource, "resource loaded through SAX InputSource");
	}

	/**
	 * Load bean definitions from the specified XML file.
	 * @param inputSource the SAX InputSource to read from
	 * @param resourceDescription a description of the resource
	 * (can be {@code null} or empty)
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 */
	public int loadBeanDefinitions(InputSource inputSource, @Nullable String resourceDescription)
			throws BeanDefinitionStoreException {

		return doLoadBeanDefinitions(inputSource, new DescriptiveResource(resourceDescription));
	}


	/**
	 * Actually load bean definitions from the specified XML file.
	 * @param inputSource the SAX InputSource to read from
	 * @param resource the resource descriptor for the XML file
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of loading or parsing errors
	 * @see #doLoadDocument
	 * @see #registerBeanDefinitions
	 */
	protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
			throws BeanDefinitionStoreException {

		try {
			/**
			 * 获取对XML文件的验证模式。
			 * 加载XML文件，并得到对应的 Document。
			 * 根据返回的Document注册Bean信息。
			 */
			System.err.println("根据规则对xml格式进行验证(验证模式)");
			System.err.println("加载XML文件，并得到对应的 Document");
			Document doc = doLoadDocument(inputSource, resource);
			System.out.println("Document:" + doc.toString());
			int count = registerBeanDefinitions(doc, resource);
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + count + " bean definitions from " + resource);
			}
			return count;
		}
		catch (BeanDefinitionStoreException ex) {
			throw ex;
		}
		catch (SAXParseException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
		}
		catch (SAXException ex) {
			throw new XmlBeanDefinitionStoreException(resource.getDescription(),
					"XML document from " + resource + " is invalid", ex);
		}
		catch (ParserConfigurationException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Parser configuration exception parsing XML from " + resource, ex);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"IOException parsing XML document from " + resource, ex);
		}
		catch (Throwable ex) {
			throw new BeanDefinitionStoreException(resource.getDescription(),
					"Unexpected exception parsing XML document from " + resource, ex);
		}
	}

	/**
	 * Actually load the specified document using the configured DocumentLoader.
	 * @param inputSource the SAX InputSource to read from
	 * @param resource the resource descriptor for the XML file
	 * @return the DOM Document
	 * @throws Exception when thrown from the DocumentLoader
	 * @see #setDocumentLoader
	 * @see DocumentLoader#loadDocument
	 *
	 * 加载document 文件
	 */
	protected Document doLoadDocument(InputSource inputSource, Resource resource) throws Exception {
		return this.documentLoader.loadDocument(inputSource, getEntityResolver(), this.errorHandler,
				getValidationModeForResource(resource), isNamespaceAware());
	}

	/**
	 * Determine the validation mode for the specified {@link Resource}.
	 * If no explicit validation mode has been configured, then the validation
	 * mode gets {@link #detectValidationMode detected} from the given resource.
	 * <p>Override this method if you would like full control over the validation
	 * mode, even when something other than {@link #VALIDATION_AUTO} was set.
	 * @see #detectValidationMode
	 *
	 * 获取对应资源的的验证模式
	 */
	protected int getValidationModeForResource(Resource resource) {
		System.out.println("1：自动检测 - 2：DTD  - 3：XSD");
		int validationModeToUse = getValidationMode();
		// 如果手动指定了验证仪式则使用指定的验证模式
		System.err.println("是否手动指定了验证仪式则使用指定的验证模式:" + validationModeToUse);
		if (validationModeToUse != VALIDATION_AUTO) {
			return validationModeToUse;
		}
		// 如果未指定则使用向动检测
		int detectedMode = detectValidationMode(resource);
		System.err.println("如果未指定则使用向动检测:" +detectedMode);
		if (detectedMode != VALIDATION_AUTO) {
			return detectedMode;
		}
		// Hmm, we didn't get a clear indication... Let's assume XSD,
		// since apparently no DTD declaration has been found up until
		// detection stopped (before finding the document's root tag).
		System.out.println("如果都没指定用XSD  对应值为3");
		return VALIDATION_XSD;
	}

	/**
	 * Detect which kind of validation to perform on the XML file identified
	 * by the supplied {@link Resource}. If the file has a {@code DOCTYPE}
	 * definition then DTD validation is used otherwise XSD validation is assumed.
	 * <p>Override this method if you would like to customize resolution
	 * of the {@link #VALIDATION_AUTO} mode.
	 *
	 * 检测对提供的标识的 XML 文件执行哪种验证。
	 * 如果文件具有DOCTYPE定义，则使用DTD验证，否则假定 XSD 验证。
	 * 如果您想自定义VALIDATION_AUTO模式的分辨率，请覆盖此方法。
	 *
	 * 自动检测验证模式的功能
	 * 在detectValidationMode 函数中又将向动检测剧正模式的工作委托给了专门处理类 XmlValidationModeDetector ，
	 * 调用了 XmlValidationModeDetector 的 detectValidationMode 方法
	 * Spring 来检
	 *
	 * 测验证模式的办法就是判断是荷包含DOCTYPE，如果含就是DTD，否则就XSD。
	 */
	protected int detectValidationMode(Resource resource) {
		if (resource.isOpen()) {
			throw new BeanDefinitionStoreException(
					"Passed-in Resource [" + resource + "] contains an open stream: " +
					"cannot determine validation mode automatically. Either pass in a Resource " +
					"that is able to create fresh streams, or explicitly specify the validationMode " +
					"on your XmlBeanDefinitionReader instance.");
		}

		InputStream inputStream;
		try {
			inputStream = resource.getInputStream();
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException(
					"Unable to determine validation mode for [" + resource + "]: cannot open InputStream. " +
					"Did you attempt to load directly from a SAX InputSource without specifying the " +
					"validationMode on your XmlBeanDefinitionReader instance?", ex);
		}

		try {
			return this.validationModeDetector.detectValidationMode(inputStream);
		}
		catch (IOException ex) {
			throw new BeanDefinitionStoreException("Unable to determine validation mode for [" +
					resource + "]: an error occurred whilst reading from the InputStream.", ex);
		}
	}

	/**
	 * Register the bean definitions contained in the given DOM document.
	 * Called by {@code loadBeanDefinitions}.
	 * <p>Creates a new instance of the parser class and invokes
	 * {@code registerBeanDefinitions} on it.
	 * @param doc the DOM document
	 * @param resource the resource descriptor (for context information)
	 * @return the number of bean definitions found
	 * @throws BeanDefinitionStoreException in case of parsing errors
	 * @see #loadBeanDefinitions
	 * @see #setDocumentReaderClass
	 * @see BeanDefinitionDocumentReader#registerBeanDefinitions
	 *
	 * 注册包含在给定 DOM 文档中的 bean 定义。由loadBeanDefinitions调用。
	 * 创建解析器类的新实例并在其上调用registerBeanDefinitions。
	 * @param doc DOM 文档
	 * @param resource 资源描述符（用于上下文信息）
	 * @return 找到的 bean 定义的数量
	 * @throws BeanDefinitionStoreException 在解析错误的情况下
	 * @see #loadBeanDefinitions
	 * @see #setDocumentReaderClass
	 * @see # BeanDefinitionDocumentReader #registerBeanDefinitions
	 */
	public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException {
		// 使用DefaultBeanDefinitionDocumentReader 实例化BeanDefinitionDocumentReader
		System.err.println("使用DefaultBeanDefinitionDocumentReader 实例化BeanDefinitionDocumentReader");
		BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
		// 在实例化BeanDefinitionReader 时候会将 BeanDefinitionRegistry传入默认使用继承自DefaultListableBeanFactory
		System.out.println("在实例化BeanDefinitionReader 时候会将 BeanDefinitionRegistry传入默认使用继承自DefaultListableBeanFactory");
		// 记录统计前BeanDefinition的加载个数
		System.err.println("记录统计前BeanDefinition的加载个数，BeanDefinition实际是个map");
		int countBefore = getRegistry().getBeanDefinitionCount();
		System.err.println("统计当前bean的注册个数:" + countBefore);
		// 加载及注册bean
		documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
		// 记录本次加载的 BeanDefinition
		return getRegistry().getBeanDefinitionCount() - countBefore;
	}

	/**
	 * Create the {@link BeanDefinitionDocumentReader} to use for actually
	 * reading bean definitions from an XML document.
	 * <p>The default implementation instantiates the specified "documentReaderClass".
	 * @see #setDocumentReaderClass
	 */
	protected BeanDefinitionDocumentReader createBeanDefinitionDocumentReader() {
		System.out.println("从xml中读取 bean 并实例化BeanDefinitionDocumentReader");
		return BeanUtils.instantiateClass(this.documentReaderClass);
	}

	/**
	 * Create the {@link XmlReaderContext} to pass over to the document reader.
	 */
	public XmlReaderContext createReaderContext(Resource resource) {
		return new XmlReaderContext(resource, this.problemReporter, this.eventListener,
				this.sourceExtractor, this, getNamespaceHandlerResolver());
	}

	/**
	 * Lazily create a default NamespaceHandlerResolver, if not set before.
	 * @see #createDefaultNamespaceHandlerResolver()
	 */
	public NamespaceHandlerResolver getNamespaceHandlerResolver() {
		if (this.namespaceHandlerResolver == null) {
			this.namespaceHandlerResolver = createDefaultNamespaceHandlerResolver();
		}
		return this.namespaceHandlerResolver;
	}

	/**
	 * Create the default implementation of {@link NamespaceHandlerResolver} used if none is specified.
	 * <p>The default implementation returns an instance of {@link DefaultNamespaceHandlerResolver}.
	 * @see DefaultNamespaceHandlerResolver#DefaultNamespaceHandlerResolver(ClassLoader)
	 */
	protected NamespaceHandlerResolver createDefaultNamespaceHandlerResolver() {
		ClassLoader cl = (getResourceLoader() != null ? getResourceLoader().getClassLoader() : getBeanClassLoader());
		return new DefaultNamespaceHandlerResolver(cl);
	}

}