Java解析Xml的三种方式总结

转自：http://blog.csdn.net/zjf280441589/article/details/50613881

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 beanid CDATA #REQUIREDclass CDATA #REQUIRED><!ELEMENT property EMPTY><!ATTLIST propertyname CDATA #REQUIREDvalue CDATA #IMPLIEDref CDATA #IMPLIED>

JAXP-Dom

/*** @author jifang* @since 16/1/13下午11:24.*/
public class XmlRead {@Testpublic 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

`Node`常用方法	释义
`Node appendChild(Node newChild)`	Adds the node newChild to the end of the list of children of this node.
`Node removeChild(Node oldChild)`	Removes the child node indicated by oldChild from the list of children, and returns it.
`NodeList getChildNodes()`	A NodeList that contains all children of this node.
`NamedNodeMap getAttributes()`	A NamedNodeMap containing the attributes of this node (if it is an Element) or null otherwise.
`String getTextContent()`	This attribute returns the text content of this node and its descendants.

Document

`Document`常用方法	释义
`NodeList getElementsByTagName(String tagname)`	Returns a NodeList of all the Elements in document order with a given tag name and are contained in the document.
`Element createElement(String tagName)`	Creates an element of the type specified.
`Text createTextNode(String data)`	Creates a Text node given the specified string.
`Attr createAttribute(String name)`	Creates an Attr of the given name.

Dom查询

解析<bean/>标签上的所有属性

public class XmlRead {private Document document;@Beforepublic void setUp() throws ParserConfigurationException, IOException, SAXException {document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(ClassLoader.getSystemResourceAsStream("config.xml"));}@Testpublic 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;@Beforepublic void setUp() throws ParserConfigurationException, IOException, SAXException {document = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(ClassLoader.getSystemResourceAsStream("config.xml"));}@Testpublic 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);}@Afterpublic void tearDown() throws TransformerException {transformer = TransformerFactory.newInstance().newTransformer();// 写回XMLtransformer.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 {@Testpublic void client() throws ParserConfigurationException, IOException, SAXException {SAXParser parser = SAXParserFactory.newInstance().newSAXParser();parser.parse(ClassLoader.getSystemResourceAsStream("config.xml"), new SaxHandler());}private class SaxHandler extends DefaultHandler {@Overridepublic 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(">");}@Overridepublic void characters(char[] ch, int start, int length) throws SAXException {System.out.print(new String(ch, start, length));}@Overridepublic 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();@Overridepublic void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {if (qName.equals("property")) {mutex.lock();isProperty = true;}}@Overridepublic void characters(char[] ch, int start, int length) throws SAXException {// 只有被锁定之后才有可能是trueif (isProperty) {System.out.println(new String(ch, start, length));}}@Overridepublic 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 {@Testpublic 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

`Node`常用方法	释义
`Element getParent()`	getParent returns the parent Element if this node supports the parent relationship or null if it is the root element or does not support the parent relationship.

Document

`Document`常用方法	释义
`Element getRootElement()`	Returns the root Elementfor this document.

Element

`Element`常用方法	释义
`void add(Attribute/Text param)`	Adds the given Attribute/Text to this element.
`Element addAttribute(String name, String value)`	Adds the attribute value of the given local name.
`Attribute attribute(int index)`	Returns the attribute at the specified indexGets the
`Attribute attribute(String name)`	Returns the attribute with the given name
`Element element(String name)`	Returns the first element for the given local name and any namespace.
`Iterator elementIterator()`	Returns an iterator over all this elements child elements.
`Iterator elementIterator(String name)`	Returns an iterator over the elements contained in this element which match the given local name and any namespace.
`List elements()`	Returns the elements contained in this element.
`List elements(String name)`	Returns the elements contained in this element with the given local name and any namespace.

Branch

`Branch`常用方法	释义
`Element addElement(String name)`	Adds a new Element node with the given name to this branch and returns a reference to the new node.
`boolean remove(Node node)`	Removes the given Node if the node is an immediate child of this 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;@Beforepublic 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 {//...@Testpublic 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");}@Afterpublic void tearDown() throws IOException {// 回写XMLOutputFormat 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;@Beforepublic 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);}@Afterpublic 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.

表达式	描述
`/`	从根节点开始获取(`/beans`:匹配根下的`<beans/>`; `/beans/bean`:匹配`<beans/>`下面的`<bean/>`)
`//`	从当前文档中搜索,而不用考虑它们的位置(`//property`: 匹配当前文档中所有`<property/>`)
`*`	匹配任何元素节点(`/*`: 匹配所有标签)
`@`	匹配属性(例: `//@name`: 匹配所有`name`属性)
`[position]`	位置谓语匹配(例: `//property[1]`: 匹配第一个`<property/>`;`//property[last()]`: 匹配最后一个`<property/>`)
`[@attr]`	属性谓语匹配(例: `//bean[@id]`: 匹配所有带id属性的标签; `//bean[@id='id1']`: 匹配所有id属性值为’id1’的标签)

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:

方法
`List selectNodes(String xpathExpression)`
`List selectNodes(String xpathExpression, String comparisonXPathExpression)`
`List selectNodes(String xpathExpression, String comparisonXPathExpression, boolean removeDuplicates)`
`Object selectObject(String xpathExpression)`
`Node selectSingleNode(String xpathExpression)`

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;@Beforepublic 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);
}