Java 解析 XML

XML解析技術有兩種 DOM SAX

• DOM方式

根據XML的層級結構在內存中分配一個樹形結構,把XML的標簽,屬性和文本等元素都封裝成樹的節點對象

• 優點: 便于實現增 刪 改 查
• 缺點: XML文件過大可能造成內存溢出

• SAX方式

采用事件驅動模型邊讀邊解析:從上到下一行行解析,解析到某一元素, 調用相應解析方法

• 優點: 不會造成內存溢出,
• 缺點: 查詢不方便,但不能實現 增 刪 改

不同的公司和組織提供了針對DOM和SAX兩種方式的解析器

• SUN的jaxp
• Dom4j組織的dom4j(最常用:如Spring)
• JDom組織的jdom

關于這三種解析器淵源可以參考java解析xml文件四種方式.

JAXP 解析

JAXP是JavaSE的一部分,在javax.xml.parsers包下,分別針對dom與sax提供了如下解析器:

Dom

• DocumentBuilder
• DocumentBuilderFactory

SAX

• SAXParser
• SAXParserFactory

示例XML如下,下面我們會使用JAXP對他進行增 刪 改 查操作

• config.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE beans SYSTEM "constraint.dtd">
<beans>
 <bean id="id1" class="com.fq.domain.Bean">
 <property name="isUsed" value="true"/>
 </bean>
 <bean id="id2" class="com.fq.domain.ComplexBean">
 <property name="refBean" ref="id1"/>
 </bean>
</beans>

• constraint.dtd

<!ELEMENT beans (bean*) >
 <!ELEMENT bean (property*)>
 <!ATTLIST bean
 id CDATA #REQUIRED
 class CDATA #REQUIRED
 >
<!ELEMENT property EMPTY>
 <!ATTLIST property
 name CDATA #REQUIRED
 value CDATA #IMPLIED
 ref CDATA #IMPLIED>

JAXP-Dom

/**
 * @author jifang
 * @since 16/1/13下午11:24.
 */
public class XmlRead {
@Test
 public void client() throws ParserConfigurationException, IOException, SAXException {
 // 生成一個Dom解析器
 DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
// 解析XML文件
 Document document = builder.parse(ClassLoader.getSystemResourceAsStream("config.xml"));
// ...
 }
}

DocumentBuilder的parse(String/File/InputSource/InputStream param)方法可以將一個XML文件解析為一個Document對象,代表整個文檔.Document(org.w3c.dom包下)是一個接口,其父接口為Node, Node的其他子接口還有Element Attr Text等.

• Node

• Document

Dom查詢

• 解析<bean/>標簽上的所有屬性

public class XmlRead {
private Document document;
@Before
 public void setUp() throws ParserConfigurationException, IOException, SAXException {
 document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
 .parse(ClassLoader.getSystemResourceAsStream("config.xml"));
 }
@Test
 public void client() throws ParserConfigurationException, IOException, SAXException {
 NodeList beans = document.getElementsByTagName("bean");
 for (int i = 0; i < beans.getLength(); ++i) {
 NamedNodeMap attributes = beans.item(i).getAttributes();
 scanNameNodeMap(attributes);
 }
 }
private void scanNameNodeMap(NamedNodeMap attributes) {
 for (int i = 0; i < attributes.getLength(); ++i) {
 Attr attribute = (Attr) attributes.item(i);
 System.out.printf("%s -> %s%n", attribute.getName(), attribute.getValue());
 // System.out.println(attribute.getNodeName() + " -> " + attribute.getTextContent());
 }
 }
}

• 打印XML文件所有標簽名

@Test
public void client() {
 list(document, 0);
}
private void list(Node node, int depth) {
 if (node.getNodeType() == Node.ELEMENT_NODE) {
 for (int i = 0; i < depth; ++i)
 System.out.print("\t");
 System.out.println("<" + node.getNodeName() + ">");
 }
NodeList childNodes = node.getChildNodes();
 for (int i = 0; i < childNodes.getLength(); ++i) {
 list(childNodes.item(i), depth + 1);
 }
}

Dom添加節點

• 在第一個<bean/>標簽下添加一個<property/>標簽,最終結果形式:

<bean id="id1" class="com.fq.domain.Bean">
 <property name="isUsed" value="true"/>
 <property name="name" value="simple-bean">新添加的</property>
</bean>

/**
 * @author jifang
 * @since 16/1/17 下午5:56.
 */
public class XmlAppend {
// 文檔回寫器
 private Transformer transformer;
// xml文檔
 private Document document;
@Before
 public void setUp() throws ParserConfigurationException, IOException, SAXException {
 document = DocumentBuilderFactory.newInstance().newDocumentBuilder()
 .parse(ClassLoader.getSystemResourceAsStream("config.xml"));
 }
@Test
 public void client() {
 // 得到第一bean標簽
 Node firstBean = document.getElementsByTagName("bean").item(0);
/** 創建一個property標簽 **/
 Element property = document.createElement("property");
// 為property標簽添加屬性
 // property.setAttribute("name", "name");
 // property.setAttribute("value", "feiqing");
 Attr name = document.createAttribute("name");
 name.setValue("name");
 property.setAttributeNode(name);
 Attr value = document.createAttribute("value");
 value.setValue("simple-bean");
 property.setAttributeNode(value);
// 為property標簽添加內容
 //property.setTextContent("新添加的");
 property.appendChild(document.createTextNode("新添加的"));
// 將property標簽添加到bean標簽下
 firstBean.appendChild(property);
 }
@After
 public void tearDown() throws TransformerException {
 transformer = TransformerFactory.newInstance().newTransformer();
// 寫回XML
 transformer.transform(new DOMSource(document),
 new StreamResult("src/main/resources/config.xml"));
 }
}

注意: 必須將內存中的DOM寫回XML文檔才能生效

Dom更新節點

• 將剛剛添加的<property/>修改如下

<property name="name" value="new-simple-bean">simple-bean是新添加的</property>

@Test
public void client() {
 NodeList properties = document.getElementsByTagName("property");
 for (int i = 0; i < properties.getLength(); ++i) {
 Element property = (Element) properties.item(i);
 if (property.getAttribute("value").equals("simple-bean")) {
 property.setAttribute("value", "new-simple-bean");
 property.setTextContent("simple-bean是新添加的");
 break;
 }
 }
}

Dom刪除節點

• 刪除剛剛修改的<property/>標簽

@Test
public void client() {
 NodeList properties = document.getElementsByTagName("property");
 for (int i = 0; i < properties.getLength(); ++i) {
 Element property = (Element) properties.item(i);
 if (property.getAttribute("value").equals("new-simple-bean")) {
 property.getParentNode().removeChild(property);
 break;
 }
 }
}

JAXP-SAX

SAXParser實例需要從SAXParserFactory實例的newSAXParser()方法獲得, 用于解析XML文件的parse(String uri, DefaultHandler dh)方法沒有返回值,但比DOM方法多了一個事件處理器參數DefaultHandler:

• 解析到開始標簽,自動調用DefaultHandler的startElement()方法;
• 解析到標簽內容(文本),自動調用DefaultHandler的characters()方法;
• 解析到結束標簽,自動調用DefaultHandler的endElement()方法.

Sax查詢

• 打印整個XML文檔

/**
 * @author jifang
 * @since 16/1/17 下午9:16.
 */
public class SaxRead {
@Test
 public void client() throws ParserConfigurationException, IOException, SAXException {
 SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
 parser.parse(ClassLoader.getSystemResourceAsStream("config.xml"), new SaxHandler());
 }
private class SaxHandler extends DefaultHandler {
@Override
 public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
 System.out.print("<" + qName);
 for (int i = 0; i < attributes.getLength(); ++i) {
 String attrName = attributes.getQName(i);
 String attrValue = attributes.getValue(i);
 System.out.print(" " + attrName + "=" + attrValue);
 }
 System.out.print(">");
 }
@Override
 public void characters(char[] ch, int start, int length) throws SAXException {
 System.out.print(new String(ch, start, length));
 }
@Override
 public void endElement(String uri, String localName, String qName) throws SAXException {
 System.out.print("</" + qName + ">");
 }
 }
}

• 打印所有property標簽內容的Handler

private class SaxHandler extends DefaultHandler {
 // 用互斥鎖保護isProperty變量
 private boolean isProperty = false;
 private Lock mutex = new ReentrantLock();
@Override
 public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
 if (qName.equals("property")) {
 mutex.lock();
 isProperty = true;
 }
 }
@Override
 public void characters(char[] ch, int start, int length) throws SAXException {
 // 只有被鎖定之后才有可能是true
 if (isProperty) {
 System.out.println(new String(ch, start, length));
 }
 }
@Override
 public void endElement(String uri, String localName, String qName) throws SAXException {
 if (qName.equals("property")) {
 try {
 isProperty = false;
 } finally {
 mutex.unlock();
 }
 }
 }
}

注: SAX方式不能實現增 刪 改操作.

Dom4j解析

Dom4j是JDom的一種智能分支,從原先的JDom組織中分離出來,提供了比JDom功能更加強大,性能更加卓越的Dom4j解析器(比如提供對XPath支持).使用Dom4j需要在pom中添加如下依賴:

<dependency>
 <groupId>dom4j</groupId>
 <artifactId>dom4j</artifactId>
 <version>1.6.1</version>
</dependency>

示例XML如下,下面我們會使用Dom4j對他進行增 刪 改 查操作:

config.xml
<?xml version="1.0" encoding="utf-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns="http://www.fq.me/context"
 xsi:schemaLocation="http://www.fq.me/context http://www.fq.me/context/context.xsd">
 <bean id="id1" class="com.fq.benz">
 <property name="name" value="benz"/>
 </bean>
 <bean id="id2" class="com.fq.domain.Bean">
 <property name="isUsed" value="true"/>
 <property name="complexBean" ref="id1"/>
 </bean>
</beans>

• context.xsd

<?xml version="1.0" encoding="utf-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
 targetNamespace="http://www.fq.me/context"
 elementFormDefault="qualified">
 <element name="beans">
 <complexType>
 <sequence>
 <element name="bean" maxOccurs="unbounded">
 <complexType>
 <sequence>
 <element name="property" maxOccurs="unbounded">
 <complexType>
 <attribute name="name" type="string" use="required"/>
 <attribute name="value" type="string" use="optional"/>
 <attribute name="ref" type="string" use="optional"/>
 </complexType>
 </element>
 </sequence>
 <attribute name="id" type="string" use="required"/>
 <attribute name="class" type="string" use="required"/>
 </complexType>
 </element>
 </sequence>
 </complexType>
 </element>
</schema>

/**
 * @author jifang
 * @since 16/1/18下午4:02.
 */
public class Dom4jRead {
@Test
 public void client() throws DocumentException {
 SAXReader reader = new SAXReader();
 Document document = reader.read(ClassLoader.getSystemResource("config.xml"));
 // ...
 }
}

與JAXP類似Document也是一個接口(org.dom4j包下),其父接口是Node, Node的子接口還有Element Attribute Document Text CDATA Branch等

• Node

• Document

• Element

• Branch

Dom4j查詢

• 打印所有屬性信息:

/**
 * @author jifang
 * @since 16/1/18下午4:02.
 */
public class Dom4jRead {
private Document document;
@Before
 public void setUp() throws DocumentException {
 document = new SAXReader()
 .read(ClassLoader.getSystemResource("config.xml"));
 }
@Test
 @SuppressWarnings("unchecked")
 public void client() {
 Element beans = document.getRootElement();
for (Iterator iterator = beans.elementIterator(); iterator.hasNext(); ) {
 Element bean = (Element) iterator.next();
 String id = bean.attributeValue("id");
 String clazz = bean.attributeValue("class");
 System.out.println("id: " + id + ", class: " + clazz);
scanProperties(bean.elements());
 }
 }
public void scanProperties(List<? extends Element> properties) {
 for (Element property : properties) {
 System.out.print("name: " + property.attributeValue("name"));
 Attribute value = property.attribute("value");
 if (value != null) {
 System.out.println("," + value.getName() + ": " + value.getValue());
 }
 Attribute ref = property.attribute("ref");
 if (ref != null) {
 System.out.println("," + ref.getName() + ": " + ref.getValue());
 }
 }
 }
}

Dom4j添加節點

在第一個<bean/>標簽末尾添加<property/>標簽

<bean id="id1" class="com.fq.benz"> 
 <property name="name" value="benz"/> 
 <property name="refBean" ref="id2">新添加的標簽</property>
</bean>

/**
 * @author jifang
 * @since 16/1/19上午9:50.
 */
public class Dom4jAppend {
//...
@Test
 public void client() {
 Element beans = document.getRootElement();
 Element firstBean = beans.element("bean");
 Element property = firstBean.addElement("property");
 property.addAttribute("name", "refBean");
 property.addAttribute("ref", "id2");
 property.setText("新添加的標簽");
 }
@After
 public void tearDown() throws IOException {
 // 回寫XML
 OutputFormat format = OutputFormat.createPrettyPrint();
 XMLWriter writer = new XMLWriter(new FileOutputStream("src/main/resources/config.xml"), format);
 writer.write(document);
 }
}

我們可以將獲取讀寫XML操作封裝成一個工具, 以后調用時會方便些:

/**
 * @author jifang
 * @since 16/1/19下午2:12.
 */
public class XmlUtils {
public static Document getXmlDocument(String config) {
 try {
 return new SAXReader().read(ClassLoader.getSystemResource(config));
 } catch (DocumentException e) {
 throw new RuntimeException(e);
 }
 }
public static void writeXmlDocument(String path, Document document) {
 try {
 new XMLWriter(new FileOutputStream(path), OutputFormat.createPrettyPrint()).write(document);
 } catch (IOException e) {
 throw new RuntimeException(e);
 }
 }
}

在第一個<bean/>的第一個<property/>后面添加一個<property/>標簽

<bean id="id1" class="com.fq.benz"> 
 <property name="name" value="benz"/> 
 <property name="rate" value="3.14"/>
 <property name="refBean" ref="id2">新添加的標簽</property> 
</bean>

public class Dom4jAppend {
private Document document;
@Before
 public void setUp() {
 document = XmlUtils.getXmlDocument("config.xml");
 }
@Test
 @SuppressWarnings("unchecked")
 public void client() {
 Element beans = document.getRootElement();
 Element firstBean = beans.element("bean");
 List<Element> properties = firstBean.elements();
//Element property = DocumentHelper
 // .createElement(QName.get("property", firstBean.getNamespaceURI()));
 Element property = DocumentFactory.getInstance()
 .createElement("property", firstBean.getNamespaceURI());
 property.addAttribute("name", "rate");
 property.addAttribute("value", "3.14");
 properties.add(1, property);
 }
@After
 public void tearDown() {
 XmlUtils.writeXmlDocument("src/main/resources/config.xml", document);
 }
}

Dom4j修改節點

將id1 bean的第一個<property/>修改如下:

<property name="name" value="翡青"/>

@Test
@SuppressWarnings("unchecked")
public void client() {
 Element beans = document.getRootElement();
 Element firstBean = beans.element("bean");
 List<Element> properties = firstBean.elements();
Element property = DocumentFactory.getInstance()
 .createElement("property", firstBean.getNamespaceURI());
 property.addAttribute("name", "rate");
 property.addAttribute("value", "3.14");
 properties.add(1, property);
}

Dom4j 刪除節點

刪除剛剛修改的節點

@Test
@SuppressWarnings("unchecked")
public void delete() {
 List<Element> beans = document.getRootElement().elements("bean");
 for (Element bean : beans) {
 if (bean.attributeValue("id").equals("id1")) {
 List<Element> properties = bean.elements("property");
 for (Element property : properties) {
 if (property.attributeValue("name").equals("name")) {
 // 執行刪除動作
 property.getParent().remove(property);
 break;
 }
 }
 break;
 }
 }
}

Dom4j實例

在Java 反射一文中我們實現了根據JSON配置文件來加載bean的對象池,現在我們可以為其添加根據XML配置(XML文件同前):

/**
 * @author jifang
 * @since 16/1/18下午9:18.
 */
public class XmlParse {
private static final ObjectPool POOL = ObjectPoolBuilder.init(null);
public static Element parseBeans(String config) {
 try {
 return new SAXReader().read(ClassLoader.getSystemResource(config)).getRootElement();
 } catch (DocumentException e) {
 throw new RuntimeException(e);
 }
 }
public static void processObject(Element bean, List<? extends Element> properties)
 throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchFieldException {
 Class<?> clazz = Class.forName(bean.attributeValue(CommonConstant.CLASS));
 Object targetObject = clazz.newInstance();
for (Element property : properties) {
 String fieldName = property.attributeValue(CommonConstant.NAME);
 Field field = clazz.getDeclaredField(fieldName);
 field.setAccessible(true);
 // 含有value屬性
 if (property.attributeValue(CommonConstant.VALUE) != null) {
 SimpleValueSetUtils.setSimpleValue(field, targetObject, property.attributeValue(CommonConstant.VALUE));
 } else if (property.attributeValue(CommonConstant.REF) != null) {
 String refId = property.attributeValue(CommonConstant.REF);
 Object object = POOL.getObject(refId);
 field.set(targetObject, object);
 } else {
 throw new RuntimeException("neither value nor ref");
 }
 }
POOL.putObject(bean.attributeValue(CommonConstant.ID), targetObject);
 }
}

注: 上面代碼只是對象池項目的XML解析部分,完整項目可參考git@git.oschina.net:feiqing/commons-frame.git

XPath

XPath是一門在XML文檔中查找信息的語言,XPath可用來在XML文檔中對元素和屬性進行遍歷.

謂語: 謂語用來查找某個特定的節點或者包含某個指定的值的節點.XPath的語法詳細內容可以參考W3School XPath 教程.

Dom4j對XPath的支持

默認的情況下Dom4j并不支持XPath, 需要在pom下添加如下依賴:

<dependency>
 <groupId>jaxen</groupId>
 <artifactId>jaxen</artifactId>
 <version>1.1.6</version>
</dependency>

Dom4jNode接口提供了方法對XPath支持:

XPath實現查詢

• 查詢所有bean標簽上的屬性值

/**
 * @author jifang
 * @since 16/1/20上午9:28.
 */
public class XPathRead {
private Document document;
@Before
 public void setUp() throws DocumentException {
 document = XmlUtils.getXmlDocument("config.xml");
 }
@Test
 @SuppressWarnings("unchecked")
 public void client() {
 List<Element> beans = document.selectNodes("http://bean");
 for (Element bean : beans) {
 System.out.println("id: " + bean.attributeValue("id") +
 ", class: " + bean.attributeValue("class"));
 }
 }
}

XPath實現更新

• 刪除id=”id2”的<bean/>

@Test
public void client() {
 Node bean = document.selectSingleNode("http://bean[@id=\"id2\"]");
 bean.getParent().remove(bean);
}