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目录

分析

DefaultDocumentLoader#loadDocument方法是标准的 SAX 解析xml文件的代码，没有什么特殊处理的地方。

问题：

EntityResolver 解决 DTD 或XSD文件通过网络下载比较慢的问题，解决方案是本地获取 DTD或 XSD 文件。

DefaultDocumentLoader源码：

详细看代码中注释

package org.springframework.beans.factory.xml;import javax.xml.parsers.DocumentBuilder;import javax.xml.parsers.DocumentBuilderFactory;import javax.xml.parsers.ParserConfigurationException;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.springframework.lang.Nullable;import org.w3c.dom.Document;import org.xml.sax.EntityResolver;import org.xml.sax.ErrorHandler;import org.xml.sax.InputSource;public class DefaultDocumentLoader implements DocumentLoader {    private static final String SCHEMA_LANGUAGE_ATTRIBUTE = "http://java.sun.com/xml/jaxp/properties/schemaLanguage";    private static final String XSD_SCHEMA_LANGUAGE = "http://www.w3.org/2001/XMLSchema";    private static final Log logger = LogFactory.getLog(DefaultDocumentLoader.class);    public DefaultDocumentLoader() {    }    /**    * 这里是标准的 SAX 解析xml文件的代码，没有什么特殊处理的地方。    * 1.创建DocumentBuilderFactory    * 2.根据 DocumentBuilderFactory 创建 DocumentBuilder    * 3.DocumentBuilder 解析 InputSource 为 Document    *    *    */    public Document loadDocument(InputSource inputSource, EntityResolver entityResolver, ErrorHandler errorHandler, int validationMode, boolean namespaceAware) throws Exception {        // SAX, validationMode:2表示DTD，3表示XSD，         // namespaceAware 这里为false，表示是否可以处理命名空间，false为不可以        DocumentBuilderFactory factory = this.createDocumentBuilderFactory(validationMode, namespaceAware);        if(logger.isTraceEnabled()) {            logger.trace("Using JAXP provider [" + factory.getClass().getName() + "]");        }        // 创建 DocumentBuilder        DocumentBuilder builder = this.createDocumentBuilder(factory, entityResolver, errorHandler);        // 解析xml文件，文件通过 ClassPathResource --> EncodedResource --> InputSource        return builder.parse(inputSource);    }    protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware) throws ParserConfigurationException {        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();        factory.setNamespaceAware(namespaceAware);        if(validationMode != 0) {            factory.setValidating(true);            if(validationMode == 3) {                factory.setNamespaceAware(true);                try {                    factory.setAttribute("http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema");                } catch (IllegalArgumentException var6) {                    ParserConfigurationException pcex = new ParserConfigurationException("Unable to validate using XSD: Your JAXP provider [" + factory + "] does not support XML Schema. Are you running on Java 1.4 with Apache Crimson? Upgrade to Apache Xerces (or Java 1.5) for full XSD support.");                    pcex.initCause(var6);                    throw pcex;                }            }        }        return factory;    }    /**    * 1.创建 DocumentBuilder     * 2.配置 EntityResolver ，这是获取 DTD、XSD的方法，具体参考：https://blog.csdn.net/ruanhao1203/article/details/103489931    */    protected DocumentBuilder createDocumentBuilder(DocumentBuilderFactory factory, @Nullable EntityResolver entityResolver, @Nullable ErrorHandler errorHandler) throws ParserConfigurationException {        DocumentBuilder docBuilder = factory.newDocumentBuilder();        if(entityResolver != null) {            docBuilder.setEntityResolver(entityResolver);        }        if(errorHandler != null) {            docBuilder.setErrorHandler(errorHandler);        }        return docBuilder;    }}