1. Basic knowledge:
There are generally four methods for Java to parse XML: DOM, SAX, JDOM, and DOM4J.
2. Introduction to use
1), DOM
(1)Introduction
The interface provided by W3C (org.w3c.dom) reads the entire XML document into memory and builds a DOM tree to operate on each node. The advantage is that the entire document is always in memory, we can access any node at any time, and tree traversal is also a relatively familiar operation; the disadvantage is that it consumes memory, and we must wait until all documents are read into memory before processing.
(2) Sample code:
Copy the code code as follows:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<root>
<TelePhone>
<type name="nokia">
<price>599</price>
<operator>CMCC</operator>
</type>
<type name="xiaomi">
<price>699</price>
<operator>ChinaNet</operator>
</type>
</TelePhone>
</root>
Copy the code code as follows:
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
public class XMLHandler {
public XMLHandler(){
}
public String createXML(){
String xmlStr = null;
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder builder = factory.newDocumentBuilder();
Document document = builder.newDocument();
document.setXmlVersion("1.0");
Element root = document.createElement("root");
document.appendChild(root);
Element telephone = document.createElement("TelePhone");
Element nokia = document.createElement("type");
nokia.setAttribute("name", "nokia");
Element priceNokia = document.createElement("price");
priceNokia.setTextContent("599");
nokia.appendChild(priceNokia);
Element operatorNokia = document.createElement("operator");
operatorNokia.setTextContent("CMCC");
nokia.appendChild(operatorNokia);
telephone.appendChild(nokia);
Element xiaomi = document.createElement("type");
xiaomi.setAttribute("name", "xiaomi");
Element priceXiaoMi = document.createElement("price");
priceXiaoMi.setTextContent("699");
xiaomi.appendChild(priceXiaoMi);
Element operatorXiaoMi = document.createElement("operator");
operatorXiaoMi.setTextContent("ChinaNet");
xiaomi.appendChild(operatorXiaoMi);
telephone.appendChild(xiaomi);
root.appendChild(telephone);
TransformerFactory transFactory = TransformerFactory.newInstance();
Transformer transFormer = transFactory.newTransformer();
DOMSource domSource = new DOMSource(document);
//export string
ByteArrayOutputStream bos = new ByteArrayOutputStream();
transFormer.transform(domSource, new StreamResult(bos));
xmlStr = bos.toString();
//-------
//save as file
File file = new File("TelePhone.xml");
if(!file.exists()){
file.createNewFile();
}
FileOutputStream out = new FileOutputStream(file);
StreamResult xmlResult = new StreamResult(out);
transFormer.transform(domSource, xmlResult);
//--------
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (TransformerConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (TransformerException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return xmlStr;
}
public void parserXML(String strXML){
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder builder = factory.newDocumentBuilder();
StringReader sr = new StringReader(strXML);
InputSource is = new InputSource(sr);
Document doc = builder.parse(is);
Element rootElement = doc.getDocumentElement();
NodeList phones = rootElement.getElementsByTagName("type");
for (int i = 0; i < phones.getLength(); i++) {
Node type = phones.item(i);
String phoneName = ((Element)type).getAttribute("name");
System.out.println("Phone name = "+phoneName);
NodeList properties = type.getChildNodes();
for (int j = 0; j < properties.getLength(); j++) {
Node property = properties.item(j);
String nodeName = property.getNodeName();
if (nodeName.equals("price")) {
String price=property.getFirstChild().getNodeValue();
System.out.println("price="+price);
} else if (nodeName.equals("operator")) {
String operator=property.getFirstChild().getNodeValue();
System.out.println("operator="+operator);
}
}
}
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void main(String[] args) {
XMLHandler handler = new XMLHandler();
String xml = handler.createXML();
System.out.println(xml);
handler.parserXML(xml);
}
}
(3) The difference between Element and Node (org.w3c.dom)
The Node object is the main data type of the entire document object model. It is the most basic object in the DOM and represents the abstract node in the document tree. However, in actual use, the Node object is rarely used directly. Instead, the sub-objects Element, Attr, Text, etc. of the Node object are used.
The Element object represents an element in an HTML or XML document and is the main sub-object of the Node class. The element can contain attributes, so Element has methods for accessing its attributes.
Element is inherited from Node. Element is a small-scale definition. It must be a node containing complete information to be an element, such as <div>...</div>. But a node is not necessarily an element, and an element must be a node.
node has several subtypes: Element, Text, Attribute, RootElement, Comment, Namespace, etc.
2), SAX
3), JDOM
4), DOM4J
(1)Introduction
dom4j is currently the best in XML parsing (Hibernate and Sun's JAXM also use dom4j to parse XML). It incorporates many functions beyond basic XML document representation, including integrated XPath support, XML Schema support and Event-based processing of large or streaming documents.
When using XPATH, add jaxen.jar, otherwise the following error will occur:
Copy the code code as follows:
Exception in thread "main" java.lang.NoClassDefFoundError: org/jaxen/JaxenException
at org.dom4j.DocumentFactory.createXPath(DocumentFactory.java:230)
at org.dom4j.tree.AbstractNode.createXPath(AbstractNode.java:207)
at org.dom4j.tree.AbstractNode.selectNodes(AbstractNode.java:164)
(2) Sample code:
Copy the code code as follows:
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import org.xml.sax.InputSource;
public class XMLHandler {
public XMLHandler() {
// TODO Auto-generated constructor stub
}
public String createXML(){
String strXML = null;
Document document = DocumentHelper.createDocument();
Element root = document.addElement("root");
Element phone = root.addElement("TelePhone");
Element nokia = phone.addElement("type");
nokia.addAttribute("name", "nokia");
Element price_nokia = nokia.addElement("price");
price_nokia.addText("599");
Element operator_nokia = nokia.addElement("operator");
operator_nokia.addText("CMCC");
Element xiaomi = phone.addElement("type");
xiaomi.addAttribute("name", "xiaomi");
Element price_xiaomi = xiaomi.addElement("price");
price_xiaomi.addText("699");
Element operator_xiaomi = xiaomi.addElement("operator");
operator_xiaomi.addText("ChinaNet");
//--------
StringWriter strWtr = new StringWriter();
OutputFormat format = OutputFormat.createPrettyPrint();
format.setEncoding("UTF-8");
XMLWriter xmlWriter =new XMLWriter(strWtr, format);
try {
xmlWriter.write(document);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
strXML = strWtr.toString();
//--------
//-------
//strXML=document.asXML();
//------
//-------------
File file = new File("TelePhone.xml");
if (file.exists()) {
file.delete();
}
try {
file.createNewFile();
XMLWriter out = new XMLWriter(new FileWriter(file));
out.write(document);
out.flush();
out.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//-------------
return strXML;
}
public void parserXML(String strXML){
SAXReader reader = new SAXReader();
StringReader sr = new StringReader(strXML);
InputSource is = new InputSource(sr);
try {
Document document = reader.read(is);
Element root = document.getRootElement();
//get element
List<Element> phoneList = root.elements("TelePhone");
List<Element> typeList = phoneList.get(0).elements("type");
for (int i=0;i<typeList.size();i++){
Element element = typeList.get(i);
String phoneName = element.attributeValue("name");
System.out.println("phonename = "+phoneName);
//get all elements
List<Element> childList = element.elements();
for (int j=0;j<childList.size();j++){
Element e = childList.get(j);
System.out.println(e.getName()+"="+e.getText());
}
}
} catch (DocumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void parserXMLbyXPath(String strXML){
SAXReader reader = new SAXReader();
StringReader sr = new StringReader(strXML);
InputSource is = new InputSource(sr);
try {
Document document = reader.read(is);
List list = document.selectNodes("/root/TelePhone/type");
for(int i=0;i<list.size();i++){
Element e = (Element) list.get(i);
System.out.println("phonename="+e.attributeValue("name"));
List list1 = e.selectNodes("./*");
for(int j=0;j<list1.size();j++){
Element e1 = (Element) list1.get(j);
System.out.println(e1.getName()+"="+e1.getText());
}
}
} catch (DocumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
XMLHandler handler = new XMLHandler();
String strXML=handler.createXML();
System.out.println(strXML);
handler.parserXML(strXML);
System.out.println("-----------");
handler.parserXMLbyXPath(strXML);
}
}
5)XPATH
(1)Introduction
XPath is a language for finding information in XML documents. XPath is used to navigate through elements and attributes in XML documents.
For specific syntax introduction, please refer to: http://w3school.com.cn/xpath/index.asp
(2) Sample code:
Copy the code code as follows:
import java.io.IOException;
import java.io.StringReader;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
public class XMLHandler {
public XMLHandler() {
// TODO Auto-generated constructor stub
}
public void parserXML(String strXML){
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder builder = factory.newDocumentBuilder();
StringReader sr = new StringReader(strXML);
InputSource is = new InputSource(sr);
Document doc = builder.parse(is);
XPathFactory xFactory = XPathFactory.newInstance();
XPath xpath = xFactory.newXPath();
XPathExpression expr = xpath.compile("/root/TelePhone/type");
NodeList phones = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
for (int i = 0; i < phones.getLength(); i++) {
Node type = phones.item(i);
String phoneName = ((Element)type).getAttribute("name");
System.out.println("Phone name = "+phoneName);
XPathExpression expr1 = xpath.compile("./*");
NodeList list = (NodeList) expr1.evaluate(type, XPathConstants.NODESET);
for(int j =0;j<list.getLength();j++){
Element e1 = (Element) list.item(j);
System.out.println(e1.getNodeName()+"="+e1.getTextContent());
}
}
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (XPathExpressionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
String strXML="<?xml version=/"1.0/" encoding=/"UTF-8/" standalone=/"no/"?>"+
"<root>"+
"<TelePhone>"+
"<type name="nokia/">"+
"<price>599</price>"+
"<operator>CMCC</operator>"+
"</type>"+
"<type name="xiaomi/">"+
"<price>699</price>"+
"<operator>ChinaNet</operator>"+
"</type>"+
"</TelePhone>"+
"</root>";
XMLHandler handler = new XMLHandler();
handler.parserXML(strXML);
}
}
PS: Here are several online tools for xml operations for your reference:
Online XML/JSON conversion tool:
http://tools.VeVB.COm/code/xmljson
Online formatting XML/Online compressing XML:
http://tools.VeVB.COm/code/xmlformat
XML online compression/formatting tool:
http://tools.VeVB.COm/code/xml_format_compress