解析 xml 为Document

目录

分析

问题：EntityResolver

DefaultDocumentLoader源码：

---

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。
    1.创建DocumentBuilderFactory
    2.根据 DocumentBuilderFactory 创建 DocumentBuilder
    3.DocumentBuilder 解析 InputSource 为 Document

问题：EntityResolver

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;
    }
}