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使用 XSLT 格式化 XML

在平常工作中经常遇到要求对 XML 进行格式化的情况， XSLT相比较于写纯java代码操作 org.w3c.dom.Document 更加方便，利于维护。
下面会用一个java例子来介绍XSLT的基本用法。

场景

原始的XML

<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
<school><students><student><name>Lucy</name><gender>Female</gender></student><student><name>Lily</name><gender>Female</gender></student><student><name>Tom</name><gender>Male</gender></student></students>
</school>

想要把所有的女性选出来 放入下面的xml结构中

<?xml version="1.0" encoding="UTF-8"?>
<cityMall><store><name>Lucy</name><name>Lily</name></store>
</cityMall>

怎么用XSLT 实现这种转化呢。
如下 XSLT - formater.xml

<xsl:stylesheet version="1.0"xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:output method="xml" omit-xml-declaration="yes"encoding="UTF-8" indent="yes" /><!-- GLOBAL VARIABLES --><xsl:variable name="target" select="/school/students" /><!-- transform template --><xsl:template match="/"><cityMall><store><xsl:for-each select="$target/student"><xsl:if test="(boolean(gender ='Female'))"><xsl:copy-of select="name"></xsl:copy-of></xsl:if></xsl:for-each></store></cityMall></xsl:template>
</xsl:stylesheet>

遍历所有的 student element， 发现geneder为Female时，选择它。

怎么使用JAVA 调用它呢。

Formater.java

import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.apache.commons.io.output.ByteArrayOutputStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;
import com.ericsson.dve.jdv.m2m.core.util.M2MTransformerFactory;public class Formater {private static final Logger LOGGER = LoggerFactory.getLogger(M2MTransformerFactory.class);public static void main(String[] args) {Formater formater = new Formater();try {Document document = formater.getSrcDocument("test/META-INF/source.xml");Document transformedResponse = formater.transformDoc(document);System.out.println(formater.xml2Str(transformedResponse));} catch (Exception e) {LOGGER.error("Exception", e);}}private Document getSrcDocument(String srcFilePath) throws SAXException, IOException, ParserConfigurationException {Document document = null;File srcDocFile = new File("test/META-INF/source.xml");DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();DocumentBuilder builder;builder = factory.newDocumentBuilder();document = builder.parse(srcDocFile);return document;}private Document transformDoc(Document srcDoc) throws TransformerConfigurationException, TransformerException {DOMResult tResult = new DOMResult();M2MTransformerFactory.getTransformer("/META-INF/xslt/NewFile2.xml").transform(new DOMSource(srcDoc), tResult);Document transformedResponse = (Document) tResult.getNode();return transformedResponse;}private String xml2Str(Document document) throws TransformerException {TransformerFactory factory = TransformerFactory.newInstance();Transformer transformer = factory.newTransformer();ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();transformer.transform(new DOMSource(document), new StreamResult(byteArrayOutputStream));return byteArrayOutputStream.toString();}
}

TransformerFactory.java

import java.io.InputStream;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.URIResolver;
import javax.xml.transform.stream.StreamSource;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TransformerFactory {private static final Logger LOGGER = LoggerFactory.getLogger(TransformerFactory.class);private static javax.xml.transform.TransformerFactory factory;private static Transformer transformer = null;static {factory = javax.xml.transform.TransformerFactory.newInstance();factory.setURIResolver(new XsltURIResolver());}private TransformerFactory() {}/*** Creates Transformer from the file passed as argument.**/public static Transformer getTransformer(String xsltFileName) throws TransformerConfigurationException {if (xsltFileName == null || xsltFileName.isEmpty()) {throw new IllegalArgumentException("xslFileName argument must not be null");}try {if (transformer == null) {return factory.newTransformer(new StreamSource(TransformerFactory.class.getResourceAsStream(xsltFileName)));}return transformer;} catch (TransformerConfigurationException e) {LOGGER.error("Error creating xsl Transformer for file: {}", xsltFileName);throw e;}}/*** Transformer factory URI resolver**/static class XsltURIResolver implements URIResolver {public Source resolve(String href, String base) throws TransformerException {InputStream is = TransformerFactory.class.getResourceAsStream("/META-INF/xslt/" + href);if (is == null) {throw new TransformerException("Transformation file " + href + " not found");}return new StreamSource(is);}}
}

Note: formater.xml 应该放在Transformer.java 的相对路径 /META-INF/xslt/ 下面

之后如果需要不同格式的document，都可以直接修改formater.xml 来完成。 不仅直观，后续维护也更加方便。

XSLT 其他用法

• chose, when ,otherwise. 进行逻辑判断。

<xsl:choose><xsl:when test="ResultData"><xsl:copy-of select="ResultData/*"></xsl:copy-of></xsl:when><xsl:otherwise><xsl:copy-of select="*"></xsl:copy-of></xsl:otherwise>
</xsl:choose>

• xls:if xsl:element 动态的生成xml的element.

<xsl:if test="not(boolean(/school/student/name =''))"><xsl:element name="new_name"><xsl:value-of select="/school/student/name"></xsl:value-of></xsl:element>
</xsl:if>

优点：XSLT 还有很多其他用法方便xml的处理。特别适合于业务逻辑复杂的转换，
劣势：t比单纯的java 处理 org.w3c.dom.Document 处理速度慢。 但我并没有进行大量实验就行分析对比。只是在使用过程中发现 performance略有不足。