Android笔记（四十五） Android中的数据存储——XML（一）DOM解析器

         DOM解析XML在j2ee开发中比较常见，在Dom解析的过程中，是先把dom全部文件读入到内存中，然后使用dom的api遍历所有数据，检索想要的数据，这种方式显然是一种比较消耗内存的方式，对于像手机这样的移动设备来讲，内存是非常有限的，所以对于比较大的XML文件,不推荐使用这种方式，但是Dom也有它的优点，它比较直观，在xml文档比较小的情况下也可以考虑使用dom方式。

         代码演示：

MainActivity.java

package cn.lixyz.xmltest.activity;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

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.NodeList;
import org.xml.sax.SAXException;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import cn.lixyz.xmltest.R;
import cn.lixyz.xmltest.model.Student;

public class MainActivity extends Activity {

    private Button bt_readxml_dom, bt_writexml_dom;

    private List<Student> list;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        findView();
    }

    private void findView() {
        bt_readxml_dom = (Button) findViewById(R.id.bt_readxml_dom);
    }

    public void clickButton(View view) {
        switch (view.getId()) {
        case R.id.bt_readxml_dom:
            domReadXML();
            break;

        case R.id.bt_writexml_dom:
            domWriteXML();
            break;
        }
    }

    // dom方式生成xml
    private void domWriteXML() {
        // 生成xml文件的数据
        List<Student> dataList = createStudents();
        try {
            // 利用DocumentBuilderFactory创建一个DocumentBuilderFactory实例
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            // 利用DocumentBuilderFactory创建DocumentBuilder
            DocumentBuilder builder = factory.newDocumentBuilder();
            // 利用DocumentBuilder创建Document文件
            Document document = builder.newDocument();
            // 创建根节点Students
            Element element = document.createElement("Students");
            // 将根节点添加到document中
            document.appendChild(element);
            // 用循环将数据添加到document中
            for (int i = 0; i < dataList.size(); i++) {
                // 获取第i个数据对象
                Student student = dataList.get(i);
                // 创建student元素
                Element studentElement = document.createElement("student");
                // 设置student元素的属性id
                studentElement.setAttribute("id", student.getId() + "");
                // 把student节点添加到document中
                element.appendChild(studentElement);
                // 添加name节点
                Element name = document.createElement("name");
                // 给name元素设置值
                name.setTextContent(student.getName());
                // 添加到student节点中
                studentElement.appendChild(name);
                // 添加name节点
                Element age = document.createElement("age");
                // 给age元素设置值
                age.setTextContent(student.getAge() + "");
                // 添加到student节点中
                studentElement.appendChild(age);
            }

            // 使用TransformerFactory创建一个TransformerFactory对象
            TransformerFactory tf = TransformerFactory.newInstance();
            Transformer transformer = tf.newTransformer();
            DOMSource source = new DOMSource(document);
            // 创建文件存放在 /data/data/cn.xxx.xxx(当前包)/files
            FileOutputStream fos = openFileOutput("Dom.xml", Context.MODE_PRIVATE);
            PrintWriter pw = new PrintWriter(fos);
            StreamResult result = new StreamResult(pw);
            transformer.transform(source, result);
            Toast.makeText(MainActivity.this, "生成成功", Toast.LENGTH_LONG).show();
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (TransformerConfigurationException e) {
            e.printStackTrace();
        } catch (TransformerException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();

        }
    }

    // dom方式读取xml文件
    private void domReadXML() {
        try {
            // 利用DocumentBuilderFactory创建一个DocumentBuilderFactory实例
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            // 利用DocumentBuilderFactory创建DocumentBuilder
            DocumentBuilder builder = factory.newDocumentBuilder();
            // 加载XML文档（Document）
            FileInputStream is = this.getBaseContext().openFileInput("Dom.xml");
            // 调用完这句后XML文档解析完成，暂存在内存中
            Document document = builder.parse(is);
            // 获取文档的根结点(Element)
            Element rootElement = document.getDocumentElement();
            // 获取根结点中所有子节点的列表（NodeList）
            NodeList element = rootElement.getElementsByTagName("student");
            for (int i = 0; i < element.getLength(); i++) {
                // 使用getElementsByTagName再获取子节点列表中的需要读取的结点
                Element node = (Element) element.item(i);
                String id = node.getAttribute("id");
                String name = node.getElementsByTagName("name").item(0).getTextContent();
                int age = Integer.parseInt(node.getElementsByTagName("age").item(0).getTextContent());
                Log.d("TTTT", "id=" + id + ",name=" + name + ",age=" + age);
            }
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // 模拟生成xml的数据
    private List<Student> createStudents() {
        list = new ArrayList<Student>();
        Student s1 = new Student();
        s1.setId(11);
        s1.setName("张三");
        s1.setAge(10);
        list.add(s1);
        Student s2 = new Student();
        s2.setId(22);
        s2.setName("李四");
        s2.setAge(11);
        list.add(s2);
        Student s3 = new Student();
        s3.setId(33);
        s3.setName("王五");
        s3.setAge(12);
        list.add(s3);
        Student s4 = new Student();
        s4.setId(44);
        s4.setName("赵六");
        s4.setAge(13);
        list.add(s4);
        Student s5 = new Student();
        s5.setId(55);
        s5.setName("刘七");
        s5.setAge(14);
        list.add(s5);
        return list;
    }
}

activity_main.xml

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context="cn.lixyz.xmltest.activity.MainActivity" >

        <Button
            android:id="@+id/bt_writexml_dom"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:onClick="clickButton"
            android:text="DOM方式生成XML" />

        <Button
            android:id="@+id/bt_readxml_dom"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:onClick="clickButton"
            android:text="DOM方式读取XML" />
    </LinearLayout>

</ScrollView>

Student.java

package cn.lixyz.xmltest.model;

public class Student {

    private int id;
    private String name;
    private int age;

    public int getId() {
        return id;
    }

    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;
    }

}