Java 解析 XML

XML解析技术有两种 DOM SAX

• DOM方式

根据XML的层级结构在内存中分配一个树形结构,把XML的标签,属性和文本等元素都封装成树的节点对象

• 优点: 便于实现增 删 改 查
• 缺点: XML文件过大可能造成内存溢出

• SAX方式

采用事件驱动模型边读边解析:从上到下一行行解析,解析到某一元素, 调用相应解析方法

• 优点: 不会造成内存溢出,
• 缺点: 查询不方便,但不能实现 增 删 改

不同的公司和组织提供了针对DOM和SAX两种方式的解析器

• SUN的jaxp
• Dom4j组织的dom4j(最常用:如Spring)
• JDom组织的jdom

关于这三种解析器渊源可以参考java解析xml文件四种方式.

JAXP 解析

JAXP是JavaSE的一部分,在javax.xml.parsers包下,分别针对dom与sax提供了如下解析器:

Dom

• DocumentBuilder
• DocumentBuilderFactory

SAX

• SAXParser
• SAXParserFactory

示例XML如下,下面我们会使用JAXP对他进行增 删 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 {  // 生成一个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)方法可以将一个XML文件解析为一个Document对象,代表整个文档.Document(org.w3c.dom包下)是一个接口,其父接口为Node, Node的其他子接口还有Element Attr Text等.

• Node

• Document

Dom查询

• 解析<bean/>标签上的所有属性

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文件所有标签名

@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添加节点

• 在第一个<bean/>标签下添加一个<property/>标签,最终结果形式:

<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 { // 文档回写器  private Transformer transformer; // xml文档  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标签  Node firstBean = document.getElementsByTagName("bean").item(0); /** 创建一个property标签 **/  Element property = document.createElement("property"); // 为property标签添加属性  // 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); // 为property标签添加内容  //property.setTextContent("新添加的");  property.appendChild(document.createTextNode("新添加的")); // 将property标签添加到bean标签下  firstBean.appendChild(property);  } @After  public void tearDown() throws TransformerException {  transformer = TransformerFactory.newInstance().newTransformer(); // 写回XML  transformer.transform(new DOMSource(document),  new StreamResult("src/main/resources/config.xml"));  } }

注意: 必须将内存中的DOM写回XML文档才能生效

Dom更新节点

• 将刚刚添加的<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删除节点

• 删除刚刚修改的<property/>标签

@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实例需要从SAXParserFactory实例的newSAXParser()方法获得, 用于解析XML文件的parse(String uri, DefaultHandler dh)方法没有返回值,但比DOM方法多了一个事件处理器参数DefaultHandler:

• 解析到开始标签,自动调用DefaultHandler的startElement()方法;
• 解析到标签内容(文本),自动调用DefaultHandler的characters()方法;
• 解析到结束标签,自动调用DefaultHandler的endElement()方法.

Sax查询

• 打印整个XML文档

/**  * @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标签内容的Handler

private class SaxHandler extends DefaultHandler {  // 用互斥锁保护isProperty变量  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 {  // 只有被锁定之后才有可能是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方式不能实现增 删 改操作.

Dom4j解析

Dom4j是JDom的一种智能分支,从原先的JDom组织中分离出来,提供了比JDom功能更加强大,性能更加卓越的Dom4j解析器(比如提供对XPath支持).使用Dom4j需要在pom中添加如下依赖:

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

示例XML如下,下面我们会使用Dom4j对他进行增 删 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"));  // ...  } }

与JAXP类似Document也是一个接口(org.dom4j包下),其父接口是Node, Node的子接口还有Element Attribute Document Text CDATA Branch等

• Node

• Document

• Element

• Branch

Dom4j查询

• 打印所有属性信息:

/**  * @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添加节点

在第一个<bean/>标签末尾添加<property/>标签

<bean id="id1" class="com.fq.benz">   <property name="name" value="benz"/>   <property name="refBean" ref="id2">新添加的标签</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("新添加的标签");  } @After  public void tearDown() throws IOException {  // 回写XML  OutputFormat format = OutputFormat.createPrettyPrint();  XMLWriter writer = new XMLWriter(new FileOutputStream("src/main/resources/config.xml"), format);  writer.write(document);  } }

我们可以将获取读写XML操作封装成一个工具, 以后调用时会方便些:

/**  * @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);  }  } }

在第一个<bean/>的第一个<property/>后面添加一个<property/>标签

<bean id="id1" class="com.fq.benz">   <property name="name" value="benz"/>   <property name="rate" value="3.14"/>  <property name="refBean" ref="id2">新添加的标签</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修改节点

将id1 bean的第一个<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 删除节点

删除刚刚修改的节点

@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")) {  // 执行删除动作  property.getParent().remove(property);  break;  }  }  break;  }  } }

Dom4j实例

在Java 反射一文中我们实现了根据JSON配置文件来加载bean的对象池,现在我们可以为其添加根据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属性  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: 上面代码只是对象池项目的XML解析部分,完整项目可参考git@git.oschina.net:feiqing/commons-frame.git

XPath

XPath是一门在XML文档中查找信息的语言,XPath可用来在XML文档中对元素和属性进行遍历.

谓语: 谓语用来查找某个特定的节点或者包含某个指定的值的节点.XPath的语法详细内容可以参考W3School XPath 教程.

Dom4j对XPath的支持

默认的情况下Dom4j并不支持XPath, 需要在pom下添加如下依赖:

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

Dom4jNode接口提供了方法对XPath支持:

XPath实现查询

• 查询所有bean标签上的属性值

/**  * @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("//bean");  for (Element bean : beans) {  System.out.println("id: " + bean.attributeValue("id") +  ", class: " + bean.attributeValue("class"));  }  } }

XPath实现更新

• 删除id=”id2”的<bean/>

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