解析XML之DOM4J
概述
DOM4J是dom4j.org出品的一个开源XML解析包,Dom4j是一个易用的,开源的库, 用于XML,XPath和XSLT它应用于Java平台,采用了Java集合框架并完全支持DOM,SAX和JAXP DOM4J架包下载 http://downloads.sourceforge.net/dom4j/dom4j-1.6.1.jar DOM4J在线API http://www.javasoft.ch/dom4j-2.0.0-beta/apidocs/org/dom4j/package-summary.html jaxen(对XPath的支持) http://dist.codehaus.org/jaxen/distributions/jaxen-1.1.1.zip
Dom4j的主要接口
Node 为所有的dom4j中XML节点定义了多态行为 Branch 为能够包含子节点的节点,如XML元素(Element)和文档(Docuemnts)定义了一个公共的行为 Element定义XML 元素 Document定义了XML文档 DocumentType 定义XML DOCTYPE声明 Entity 定义 XML entity Attribute 定义了XML的属性 ProcessingInstruction 定义 XML 处理指令 CharacterData 是一个标识接口,标识基于字符的节点,如CDATA,Comment,Text CDATA定义了XML CDATA区域 Text定义XML文本节点 Comment定义了XML注释的行为
创建XML文件的两种方法
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE student SYSTEM "dom4j.dtd"> <students> <student> <name>lwc</name> <sex>boy</sex> <age>20</age> </student> <student> <name>nxj</name> <sex>girl</sex> <age>18</age> </student> </students>
转换字符串创建
package com.itlwc;
import java.io.File;
import java.io.FileWriter;
import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;
public class Dom4jTest {
public static void main(String[] args) {
String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"+
"<!DOCTYPE student SYSTEM \"dom4j.dtd\">"+
"<students>" +
"<student>" +
"<name>lwc</name>" +
"<sex>boy</sex>" +
"<age>20</age>" +
"</student>" +
"<student>" +
"<name>nxj</name>" +
"<sex>girl</sex>" +
"<age>18</age>" +
"</student>" +
"</students>";
try {
//解析XML,得到文档
Document document = DocumentHelper.parseText(xml);
//创建默认漂亮输出格式
OutputFormat format = OutputFormat.createPrettyPrint();
File file = new File("output.xml");
//将文档输出到文件保存,可指定字符编码,可指定格式化输出
XMLWriter output = new XMLWriter(new FileWriter(file), format);
output.write(document);
output.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
Dom4j的方法创建
package com.itlwc;
import java.io.File;
import java.io.FileWriter;
import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;
public class Dom4jTest {
public static void main(String[] args) {
try {
// 得到文档实例
Document document = DocumentHelper.createDocument();
document.addDocType("student", "", "dom4j.dtd");
// 创建元素
Element studentsElement = document.addElement("students");
Element student1Element = studentsElement.addElement("student");
Element name1Element = student1Element.addElement("name");
name1Element.setText("lwc");
Element sex1Element = student1Element.addElement("sex");
sex1Element.setText("boy");
Element age1Element = student1Element.addElement("age");
age1Element.setText("20");
Element student2Element = studentsElement.addElement("student");
Element name2Element = student2Element.addElement("name");
name2Element.setText("nxj");
Element sex2Element = student2Element.addElement("sex");
sex2Element.setText("girl");
Element age2Element = student2Element.addElement("age");
age2Element.setText("18");
// 创建默认漂亮输出格式
OutputFormat format = OutputFormat.createPrettyPrint();
File file = new File("output.xml");
// 将文档输出到文件保存,可指定字符编码,可指定格式化输出
XMLWriter output = new XMLWriter(new FileWriter(file), format);
output.write(document);
output.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
修改XML文件
package com.itlwc;
import java.io.File;
import java.io.FileWriter;
import java.util.Iterator;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
public class Dom4jTest {
public static void main(String[] args) {
try {
SAXReader saxReader = new SAXReader();
File file = new File("output.xml");
// 定位资源文件并获取document实例
Document document = saxReader.read(file);
// Document实例的selectNodes方法可以传入xpath,并返回一个List实例
List list = document.selectNodes("//students/student");
Iterator iter = list.iterator();
while (iter.hasNext()) {
Element element = (Element) iter.next();
Iterator iterName = element.elementIterator("name");
while (iterName.hasNext()) {
Element nameElement = (Element) iterName.next();
if ("lwc".equals(nameElement.getText())) {
// 修改文本
nameElement.setText("itlwc");
}
}
}
// 从新保存文件
XMLWriter output = new XMLWriter(new FileWriter(new File(
"students-modified.xml")));
output.write(document);
output.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
output.xml
<?xml version="1.0" encoding="UTF-8"?>
<students>
<student no="1001">
<name>lwc</name>
<sex>boy</sex>
<age>20</age>
</student>
<student no="1002">
<name>nxj</name>
<sex>girl</sex>
<age>18</age>
</student>
</students>
students-modified.xml
<?xml version="1.0" encoding="UTF-8"?>
<students>
<student no="1001">
<name>itlwc</name>
<sex>boy</sex>
<age>20</age>
</student>
<student no="1002">
<name>nxj</name>
<sex>girl</sex>
<age>18</age>
</student>
</students>
*/
遍历XML文件
<?xml version="1.0" encoding="UTF-8"?> <students> <student no="1001"> <name>lwc</name> <sex>boy</sex> <age>20</age> </student> <student no="1002"> <name>nxj</name> <sex>girl</sex> <age>18</age> </student> </students>
使用迭代遍历
package com.itlwc;
import java.io.File;
import java.util.Iterator;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
public class Dom4jTest {
public static void main(String[] args) {
try {
SAXReader saxReader = new SAXReader();
File file = new File("output.xml");
// 定位资源文件并获取document实例
Document document = saxReader.read(file);
// 获取根元素students
Element root = document.getRootElement();
System.out.println(root.getName());
// 枚举根节点下所有子节点student
Iterator iteStudent = root.elementIterator();
while (iteStudent.hasNext()) {
Element elementStudent = (Element) iteStudent.next();
System.out.println(elementStudent.getName());
// 枚举根节点下所有子节点student的子节点
Iterator iteSonNode = elementStudent.elementIterator();
while (iteSonNode.hasNext()) {
Element elementSon = (Element) iteSonNode.next();
System.out.println(elementSon.getName() + ":"
+ elementSon.getText());
}
// 枚举根节点下所有子节点student的属性
Iterator iteSonAttribute = elementStudent.attributeIterator();
while (iteSonAttribute.hasNext()) {
Attribute attribute = (Attribute) iteSonAttribute.next();
System.out.println(attribute.getName() + ":"
+ attribute.getData());
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
打印结果:
students
student
name:lwc
sex:boy
age:20
no:1001
student
name:nxj
sex:girl
age:18
no:1002
*/
使用观察者模式遍历
Visitor是GOF设计模式之一,其主要原理就是两种类互相保有对方的引用,
并且一种作为Visitor去访问许多Visitable
DOM4J中的Visitor模式只需要自定一个类实现Visitor接口即可
public class MyVisitor extends VisitorSupport {
public void visit(Element element) {
System.out.println(element.getName());
}
public void visit(Attribute attr) {
System.out.println(attr.getName());
}
}
调用:root.accept(new MyVisitor())
Visitor接口提供多种Visit()的重载,根据XML不同的对象,将采用不同的方式来访问
上面是给出的Element和Attribute的简单实现,一般比较常用的就是这两个
VisitorSupport是DOM4J提供的默认适配器,Visitor接口的Default Adapter模式,
这个模式给出了各种visit(*)的空实现,以便简化代码
注意,这个Visitor是自动遍历所有子节点的,
如果是root.accept(MyVisitor),将遍历子节点
案例
package com.itlwc;
import java.io.File;
import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.ProcessingInstruction;
import org.dom4j.VisitorSupport;
import org.dom4j.io.SAXReader;
/**
* 定义自己的访问者类
*/
class MyVisitor extends VisitorSupport {
// 对于属性节点,打印属性的名字和值
public void visit(Attribute node) {
System.out.println("attribute : " + node.getName() + " = "
+ node.getValue());
}
// 对于处理指令节点,打印处理指令目标和数据
public void visit(ProcessingInstruction node) {
System.out.println("PI : " + node.getTarget() + " " + node.getText());
}
// 对于元素节点,判断是否只包含文本内容,如是,则打印标记的名字和 元素的内容,如果不是,则只打印标记的名字
public void visit(Element node) {
if (node.isTextOnly()) {
System.out.println("element : " + node.getName() + " = "
+ node.getText());
} else {
System.out.println("-----" + node.getName() + "-----");
}
}
}
public class Dom4jTest {
public static void main(String[] args) {
try {
SAXReader saxReader = new SAXReader();
File file = new File("output.xml");
// 定位资源文件并获取document实例
Document document = saxReader.read(file);
document.accept(new MyVisitor());
} catch (Exception e) {
e.printStackTrace();
}
}
}
/*
打印结果:
-----students-----
-----student-----
attribute : no = 1001
element : name = lwc
element : sex = boy
element : age = 20
-----student-----
attribute : no = 1002
element : name = nxj
element : sex = girl
element : age = 18
*/