关于在DOM4J在读取XML文件时，解释DTD的问题

近日在使用 DOM4J 的时候，遇到一个问题，现在有两个解决方法，先记下来，以便日后使用。

问题：对一个 XML 文件进行读写操作，但是发现当文件存在的时候，使用DOM4J读进来的时候，生成的 Document 对象会根据 DTD 里的定义，追加了一些 default 属性（实际不需要）。而且在读取的时间被延长。

有一个 XML 文件如下：<o:p></o:p>

xml 代码

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
  ....
</beans>

使用 DOM4J 的读取文件的一般性写法：<o:p></o:p>

java 代码

SAXReader reader = new SAXReader(false);
document = reader.read(file);
root = document.getRootElement();

对象 document 里的节点会被自动追加 DTD 里的定义的 default 属性，只有新增加的节点不受影响，如下。而且，如果文件的操作时间被延长。

xml 代码

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

<beans default-lazy-init="false" default-autowire="no" default-dependency-check="none">
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase" lazy-init="default" autowire="default" dependency-check="default"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase"/>
  <bean id="OperateXmlByDom4jTestCase" class="test.OperateXmlByDom4jTestCase"/>
</beans>

<o:p></o:p>

为了不让生成我们不需要的 default 属性和缩短文件的操作时间，我们可以调用 SAXReader.setFeature 方法来改变 DOM4J 的行为，片断代码如下：<o:p></o:p>

java 代码

// http://apache.org/xml/features/nonvalidating/load-external-dtd"
saxReader.setFeature(
    Constants.XERCES_FEATURE_PREFIX + Constants.LOAD_EXTERNAL_DTD_FEATURE,
    false);

关于更多的 Feature 请参考 com.sun.org.apache.xerces.internal.impl.Constants<o:p></o:p>

以下为片断代码：<o:p></o:p>

java 代码

// xerces features

/** Xerces features prefix ("http://apache.org/xml/features/"). */
public static final String XERCES_FEATURE_PREFIX = "http://apache.org/xml/features/";

/** Schema validation feature ("validation/schema"). */
public static final String SCHEMA_VALIDATION_FEATURE = "validation/schema";

/** Expose schema normalized values */
public static final String SCHEMA_NORMALIZED_VALUE = "validation/schema/normalized-value";

/** Send schema default value via characters() */
public static final String SCHEMA_ELEMENT_DEFAULT = "validation/schema/element-default";

/** Schema full constraint checking ("validation/schema-full-checking"). */
public static final String SCHEMA_FULL_CHECKING = "validation/schema-full-checking";

/** Augment Post-Schema-Validation-Infoset */
public static final String SCHEMA_AUGMENT_PSVI = "validation/schema/augment-psvi";

/** Dynamic validation feature ("validation/dynamic"). */
public static final String DYNAMIC_VALIDATION_FEATURE = "validation/dynamic";

/** Warn on duplicate attribute declaration feature ("validation/warn-on-duplicate-attdef"). */
public static final String WARN_ON_DUPLICATE_ATTDEF_FEATURE = "validation/warn-on-duplicate-attdef";

/** Warn on undeclared element feature ("validation/warn-on-undeclared-elemdef"). */
public static final String WARN_ON_UNDECLARED_ELEMDEF_FEATURE = "validation/warn-on-undeclared-elemdef";

/** Warn on duplicate entity declaration feature ("warn-on-duplicate-entitydef"). */
public static final String WARN_ON_DUPLICATE_ENTITYDEF_FEATURE = "warn-on-duplicate-entitydef";

/** Allow Java encoding names feature ("allow-java-encodings"). */
public static final String ALLOW_JAVA_ENCODINGS_FEATURE = "allow-java-encodings";

/** Disallow DOCTYPE declaration feature ("disallow-doctype-decl"). */
public static final String DISALLOW_DOCTYPE_DECL_FEATURE = "disallow-doctype-decl";

/** Continue after fatal error feature ("continue-after-fatal-error"). */
public static final String CONTINUE_AFTER_FATAL_ERROR_FEATURE = "continue-after-fatal-error";

/** Load dtd grammar when nonvalidating feature ("nonvalidating/load-dtd-grammar"). */
public static final String LOAD_DTD_GRAMMAR_FEATURE = "nonvalidating/load-dtd-grammar";

/** Load external dtd when nonvalidating feature ("nonvalidating/load-external-dtd"). */
public static final String LOAD_EXTERNAL_DTD_FEATURE = "nonvalidating/load-external-dtd";

/** Defer node expansion feature ("dom/defer-node-expansion"). */
public static final String DEFER_NODE_EXPANSION_FEATURE = "dom/defer-node-expansion";

/** Create entity reference nodes feature ("dom/create-entity-ref-nodes"). */
public static final String CREATE_ENTITY_REF_NODES_FEATURE = "dom/create-entity-ref-nodes";

/** Include ignorable whitespace feature ("dom/include-ignorable-whitespace"). */
public static final String INCLUDE_IGNORABLE_WHITESPACE = "dom/include-ignorable-whitespace";

/** Default attribute values feature ("validation/default-attribute-values"). */
public static final String DEFAULT_ATTRIBUTE_VALUES_FEATURE = "validation/default-attribute-values";

/** Validate content models feature ("validation/validate-content-models"). */
public static final String VALIDATE_CONTENT_MODELS_FEATURE = "validation/validate-content-models";

/** Validate datatypes feature ("validation/validate-datatypes"). */
public static final String VALIDATE_DATATYPES_FEATURE = "validation/validate-datatypes";

/** Notify character references feature (scanner/notify-char-refs"). */
public static final String NOTIFY_CHAR_REFS_FEATURE = "scanner/notify-char-refs";

/** Notify built-in (&, etc.) references feature (scanner/notify-builtin-refs"). */
public static final String NOTIFY_BUILTIN_REFS_FEATURE = "scanner/notify-builtin-refs";

/** Standard URI conformant feature ("standard-uri-conformant"). */
public static final String STANDARD_URI_CONFORMANT_FEATURE = "standard-uri-conformant";

/** Internal performance related feature:
 * false - the parser settings (features/properties) have not changed between 2 parses
 * true - the parser settings have changed between 2 parses
 * NOTE: this feature should only be set by the parser configuration.
 */
public static final String PARSER_SETTINGS = "internal/parser-settings";

/** Feature to make XML Processor XInclude Aware */
public static final String XINCLUDE_AWARE = "xinclude-aware";

/** Ignore xsi:schemaLocation and xsi:noNamespaceSchemaLocation. */
public static final String IGNORE_SCHEMA_LOCATION_HINTS = "validation/schema/ignore-schema-location-hints";

/**
 * When true, the schema processor will change characters events
 * to ignorableWhitespaces events, when characters are expected to
 * only contain ignorable whitespaces.
 */
public static final String CHANGE_IGNORABLE_CHARACTERS_INTO_IGNORABLE_WHITESPACES =
    "validation/change-ignorable-characters-into-ignorable-whitespaces";

除通过上面的 SAXReader.setFeature 文件之外 ，我们还可以通过自己的 EntityResolver 来解决这个问题。<o:p></o:p>

PS：这个方法是从凝香小筑的BLOG里的一编主题是：Do not resolve DTD files when dom4j read xml file 的文章里看到的。地址：http://blog.csdn.net/lessoft/archive/<st1:chsdate w:st="on" isrocdate="False" islunardate="False" day="20" month="6" year="2007">2007/06/20</st1:chsdate>/1659579.aspx<o:p></o:p>

代码片断如下：<o:p></o:p>

java 代码

saxReader.setEntityResolver(new EntityResolver() {

    String emptyDtd = "";

    ByteArrayInputStream bytels = new ByteArrayInputStream(emptyDtd.getBytes());

    public InputSource resolveEntity(String publicId, String systemId)
           throws SAXException, IOException {
        return new InputSource(bytels);
    }
});

<o:p> </o:p>

完整的代码如下：<o:p></o:p>

java 代码

package test;

import java.io.BufferedWriter;
import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

import junit.framework.TestCase;

import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import org.dom4j.tree.DefaultDocumentType;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import com.sun.org.apache.xerces.internal.impl.Constants;

/**
 * A test case class for read and writer a xml file by Dom4j.
 * @author X.F.Yang [2007/07/03]
 * @version 1.0
 */
public class OperateXmlByDom4jTestCase extends TestCase {

    /**
     * Default way to read and writer a xml file by Dom4j.
     * @throws Exception
     */
    public void testWriteXml() throws Exception {
        XmlFileOperation operation = new XmlFileOperation();
        operation.writer(new SAXReaderWrapper() {
            public void operation(SAXReader saxReader) throws Exception {
                // Nothing to do.
            }
        });
    }

    /**
     * Do not resolve DTD files when dom4j read xml file via the set feature.
     * @throws Exception
     */
    public void testWriteXmlSetFeature() throws Exception {
        XmlFileOperation operation = new XmlFileOperation();
        operation.writer(new SAXReaderWrapper() {
            public void operation(SAXReader saxReader) throws Exception {
                // http://apache.org/xml/features/nonvalidating/load-external-dtd"
                saxReader.setFeature(
                        Constants.XERCES_FEATURE_PREFIX + Constants.LOAD_EXTERNAL_DTD_FEATURE,
                        false);
            }
        });
    }

    /**
     * Do not resolve DTD files when dom4j read xml file via implement {@link EntityResolver}.
     * @throws Exception
     */
    public void testWriteXmlEntityResolver() throws Exception {
        XmlFileOperation operation = new XmlFileOperation();
        operation.writer(new SAXReaderWrapper() {
            public void operation(SAXReader saxReader) throws Exception {
                saxReader.setEntityResolver(new EntityResolver() {

                    String emptyDtd = "";

                    ByteArrayInputStream bytels = new ByteArrayInputStream(emptyDtd.getBytes());

                    public InputSource resolveEntity(String publicId,
                            String systemId) throws SAXException, IOException {
                        return new InputSource(bytels);
                    }
                });
            }
        });
    }

    /** */
    protected interface SAXReaderWrapper {

        /** operation {@link SAXReader} */
        void operation(SAXReader saxReader) throws Exception;

    }

    /**
     * when the target file was existed, read and append the new element.
     * else, create a new xml file and add the new element.
     */
    protected class XmlFileOperation {

        /** target file */
        private File file;

        public XmlFileOperation() {
            // target file
            file = new File("d:\\spring.xml");
        }

        /**
         * Write xml file
         * @param wrapper
         * @throws Exception
         * @see {@link SAXReaderWrapper}
         */
        public void writer(SAXReaderWrapper wrapper) throws Exception {
            try {
                Document document = null;
                Element root = null;

                // read the xml file if target file was existed
                if (file.exists()) {
                    SAXReader reader = new SAXReader(false);

                    wrapper.operation(reader);

                    document = reader.read(file);
                    root = document.getRootElement();
                // if the target file was not existed, create a new one
                } else {
                    document = DocumentHelper.createDocument();
                    document.setDocType(new DefaultDocumentType("beans",
                            "-//SPRING//DTD BEAN//EN",
                            "http://www.springframework.org/dtd/spring-beans.dtd"));
                    root = document.addElement("beans");
                }
                // create the element under the root element
                root.addElement("bean")
                    .addAttribute("id", "OperateXmlByDom4jTestCase")
                    .addAttribute("class", "test.OperateXmlByDom4jTestCase");

                // writer the document
                writer(document);
            } catch (Exception e) {
                e.printStackTrace();
                throw e;
            }
        }

        protected void writer(Document document) throws Exception {
            XMLWriter xmlWriter = null;
            try {
                final OutputFormat format = OutputFormat.createPrettyPrint();
                xmlWriter = new XMLWriter(new BufferedWriter(new FileWriter(file)), format);
                xmlWriter.write(document);
            } finally {
                if (null != xmlWriter) {
                    xmlWriter.flush();
                    xmlWriter.close();
                }
            }
        }
    }
}

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