JAVA 解析 XML

XML文件时很多项目经常使用的配置或者其他用途的文件格式，解析xml文件格式的开发包也很多，本文主要使用java自带的DOM解析包。本文以一个实际例子来讲述解析xml文件的过程。

目标：解析这样一个XML文件

employees.xml

=======内容开始========

<?xml version="1.0" encoding="UTF-8"?>
<Personnel>
<Employee type="permanent">
<Name>Seagull</Name>
<Id>3674</Id>
<Age>34</Age>
</Employee>
<Employee type="contract">
<Name>Robin</Name>
<Id>3675</Id>
<Age>25</Age>
</Employee>
<Employee type="permanent">
<Name>Crow</Name>
<Id>3676</Id>
<Age>28</Age>
</Employee>
</Personnel>

=======内容结束========

目标是：输出如下内容

Employee Details - Name:Seagull, Type:permanent, Id:3674, Age:34.

Employee Details - Name:Robin, Type:contract, Id:3675, Age:25.

Employee Details - Name:Crow, Type:permanent, Id:3676, Age:28.

主要步骤

1，

• Get a document builder using document builder factory and parse the xml file to create a DOM object
• Get a list of employee elements from the DOM
• For each employee element get the id, name, age and type. Create an employee value object and add it to the list.
• At the end iterate through the list and print the employees to verify we parsed it right.

a) 获取document builder

	public void parseXmlFile(){
		//get the factory
		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
		try {
			//Using factory get an instance of document builder
			DocumentBuilder db = dbf.newDocumentBuilder();
			//parse using builder to get DOM representation of the XML file
			System.out.println("start to parse");
			org.w3c.dom.Document dom = db.parse("employees.xml");
			 parseDocument(dom);

		}catch(ParserConfigurationException pce) {
			pce.printStackTrace();
		}catch(SAXException se) {
			se.printStackTrace();
		}catch(IOException ioe) {
			ioe.printStackTrace();
		}
	}

b) 获取employee elements列表
Get the rootElement from the DOM object.From the root element get all employee elements. Iterate through each employee element to load the data.

	private void parseDocument(Document dom){
		
		//get the root element
		Element docEle = dom.getDocumentElement();
       
		//get a nodelist of elements
		NodeList nl = docEle.getElementsByTagName("Employee");
		if(nl != null && nl.getLength() > 0) {
			for(int i = 0 ; i < nl.getLength();i++) {
				//get the employee element
				Element el = (Element)nl.item(i);
				//get the Employee object
				Employee e = getEmployee(el);
				//add it to list
				
				myEmpls.add(e);
			}
		}
	}

c)读取每个员工的信息

/**
	 * I take an employee element and read the values in, create
	 * an Employee object and return it
	 */
	private Employee getEmployee(Element empEl) {
        
		//for each <employee> element get text or int values of
		//name ,id, age and name
		String name = getTextValue(empEl,"Name");
		int id = getIntValue(empEl,"Id");
		int age = getIntValue(empEl,"Age");
		String type = empEl.getAttribute("type");
		//Create a new Employee with the value read from the xml nodes
		Employee e = new Employee(name,id,age,type);
		return e;
	}
	
	/**
	 * I take a xml element and the tag name, look for the tag and get
	 * the text content
	 * i.e for <employee><name>John</name></employee> xml snippet if
	 * the Element points to employee node and tagName is 'name' I will return John
	 */
	private String getTextValue(Element ele, String tagName) {
		String textVal = null;
		NodeList nl = ele.getElementsByTagName(tagName);
		if(nl != null && nl.getLength() > 0) {
			Element el = (Element)nl.item(0);
			textVal = el.getFirstChild().getNodeValue();
		}
		return textVal;
	}

	/**
	 * Calls getTextValue and returns a int value
	 */
	private int getIntValue(Element ele, String tagName) {
		//in production application you would catch the exception
		return Integer.parseInt(getTextValue(ele,tagName));
	}
    

d) I打印输出

public void printData(){
		System.out.println("No of Employees '" + myEmpls.size() + "'.");
		
		for(Employee emp : myEmpls){
			System.out.println("Employee Details -"+
					"Name:"+emp.getName()+"  ID:"+emp.getID()+"  Age:" +emp.getAge()+"  Type:"+emp.getType());
		}
	}

截图：