Android：Dom解析XML

     与SAX和PULL解析不同，Dom解析是将XML文件全部载入，组装成一颗Dom树，然后通过节点以及节点之间的关系来解析XML文件，占用内存比较大，一般比较推荐用SAX和PULL来解析。和前面一样用同样的例子来分析一下。

首先自定义一个XML文件：Student.xml，注意是新建file而不是xml。

<?xml version="1.0" encoding="utf-8"?>  
<students>  
    <student id="1">  
        <name>张三</name>  
        <sex>男</sex>  
        <age>18</age>  
    </student>  
    <student id="2">  
        <name>李四</name>  
        <sex>女</sex>  
        <age>19</age>  
    </student>  
    <student id="3">  
        <name>王五</name>  
        <sex>男</sex>  
        <age>20</age>  
    </student>  
</students>  

package com.example.xml_sax_demo_1;
public class Student {
	private int id;
	private String name;
	private int age;
	private String sex;
	public Student() {
		// TODO Auto-generated constructor stub
	}
	public int getId() {
		return id;
	}
	public Student(int id, String name, int age) {
		super();
		this.id = id;
		this.name = name;
		this.age = age;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	@Override
	public String toString() {
		return "Student [id=" + id + ", name=" + name + ",sex=" + sex
				+ ", age=" + age + "]";
	}
}

package com.example.xml_sax_demo_1;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;      //注意使用的包都是org.w3c.dom.*的
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends ActionBarActivity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		Button button = (Button) findViewById(R.id.button);
		button.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View arg0) {
				// TODO Auto-generated method stub
				try {
					readXML();
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		});
	}
	private void readXML() throws Exception {
		List<Student> list = new ArrayList<Student>();
		InputStream stream = this.getClass().getClassLoader()
				.getResourceAsStream("Student.xml"); // 获得输入流
		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();   //一步步下去
		DocumentBuilder builder = factory.newDocumentBuilder();
		Document document = builder.parse(stream);                       
		Element element = document.getDocumentElement();                //实例化元素     
		NodeList nodeList = element.getElementsByTagName("student");    //获得节点名为student的节点列表
		for (int i = 0; i < nodeList.getLength(); i++) {                
			Element studentElement = (Element) nodeList.item(i);    //对应上面取得的列表
			Student student = new Student();                        //每个节点实例化一个student元素
			student.setId(Integer.parseInt(studentElement.getAttribute("id")));  //取得属性
			NodeList childNodeList = studentElement.getChildNodes();             //取得子节点列表
			for (int j = 0; j < childNodeList.getLength(); j++) {                          
				// if (childNodeList.item(j).getNodeType() == Node.ELEMENT_NODE)
				// {
				if (childNodeList.item(j).getNodeName().equals("name")) {      //如果子节点名为name   
					student.setName(childNodeList.item(j).getFirstChild()  //将文本数据存储起来
							.getNodeValue());
				} else if (childNodeList.item(j).getNodeName().equals("sex")) {
					student.setSex(childNodeList.item(j).getFirstChild()
							.getNodeValue());
				} else if (childNodeList.item(j).getNodeName().equals("age")) {
					student.setAge(Integer.parseInt(childNodeList.item(j)
							.getFirstChild().getNodeValue()));
				}
				// }
			}
			list.add(student);       //在列表中添加一个student对象                                  
		}

		for (Student stu : list) {
			System.out.println(stu.toString());
		}
	}
}

小结：从代码可以看出，Dom解析是将XML文件全部载入，组装成一颗Dom树，然后通过节点以及节点之间的关系来解析XML文件的，一般是不断的循环遍历，占用内存比较大。