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Java 解析 XML
Java 解析 XML
标签: Java基础
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
- 优点: 便于实现
- 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
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;
@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
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;
@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.
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;
@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);
}
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