android XML解析技术

XML在各种开发中都广泛应用，Android也不例外。作为承载数据的一个重要角色，如何读写XML成为Android开发中一项重要的技能。今天就由我向大家介绍一下在Android平台下几种常见的XML解析和创建的方法。

在Android中，常见的XML解析器分别为SAX解析器、DOM解析器和PULL解析器，下面，我将一一向大家详细介绍。

SAX解析器：

SAX(Simple API for XML)解析器是一种基于事件的解析器，它的核心是事件处理模式，主要是围绕着事件源以及事件处理器来工作的。当事件源产生事件后，调用事件处理器相应的处理方法，一个事件就可以得到处理。在事件源调用事件处理器中特定方法的时候，还要传递给事件处理器相应事件的状态信息，这样事件处理器才能够根据提供的事件信息来决定自己的行为。

SAX解析器的优点是解析速度快，占用内存少。非常适合在Android移动设备中使用。

DOM解析器：

DOM是基于树形结构的的节点或信息片段的集合，允许开发人员使用DOM API遍历XML树、检索所需数据。分析该结构通常需要加载整个文档和构造树形结构，然后才可以检索和更新节点信息。

由于DOM在内存中以树形结构存放，因此检索和更新效率会更高。但是对于特别大的文档，解析和加载整个文档将会很耗资源。

PULL解析器：

PULL解析器的运行方式和SAX类似，都是基于事件的模式。不同的是，在PULL解析过程中，我们需要自己获取产生的事件然后做相应的操作，而不像SAX那样由处理器触发一种事件的方法，执行我们的代码。PULL解析器小巧轻便，解析速度快，简单易用，非常适合在Android移动设备中使用，Android系统内部在解析各种XML时也是用PULL解析器。

以上三种解析器，都是非常实用的解析器，我将会一一介绍。我们将会使用这三种解析技术完成一项共同的任务。

我们新建一个项目，项目结构如下：

我会在项目的assets目录中放置一个XML文档books.xml，内容如下：

<?xml version="1.0" encoding="utf-8"?>
<books>
    <book>
        <id>1001</id>
        <name>Thinking In Java</name>
        <price>80.00</price>
    </book>
    <book>
        <id>1002</id>
        <name>Core Java</name>
        <price>90.00</price>
    </book>
    <book>
        <id>1003</id>
        <name>Hello, Andriod</name>
        <price>100.00</price>
    </book>
</books>

<?xml version="1.0" encoding="utf-8"?> <books> <book> <id>1001</id> <name>Thinking In Java</name> <price>80.00</price> </book> <book> <id>1002</id> <name>Core Java</name> <price>90.00</price> </book> <book> <id>1003</id> <name>Hello, Andriod</name> <price>100.00</price> </book> </books>

然后我们分别使用以上三种解析技术解析文档，得到一个List<Book>的对象，先来看一下Book.java的代码：

package com.scott.xml.model;

public class Book {
    private int id;
    private String name;
    private float price;

    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 float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "id:" + id + ", name:" + name + ", price:" + price;
    }
}

package com.scott.xml.model; public class Book { private int id; private String name; private float price; 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 float getPrice() { return price; } public void setPrice(float price) { this.price = price; } @Override public String toString() { return "id:" + id + ", name:" + name + ", price:" + price; } }

最后，我们还要把这个集合对象中的数据生成一个新的XML文档，如图：

生成的XML结构跟原始文档略有不同，是下面这种格式：

<?xml version="1.0" encoding="UTF-8"?>
<books>
  <book id="1001">
    <name>Thinking In Java</name>
    <price>80.0</price>
  </book>
  <book id="1002">
    <name>Core Java</name>
    <price>90.0</price>
  </book>
  <book id="1003">
    <name>Hello, Andriod</name>
    <price>100.0</price>
  </book>
</books>

<?xml version="1.0" encoding="UTF-8"?> <books> <book id="1001"> <name>Thinking In Java</name> <price>80.0</price> </book> <book id="1002"> <name>Core Java</name> <price>90.0</price> </book> <book id="1003"> <name>Hello, Andriod</name> <price>100.0</price> </book> </books>

接下来，就该介绍操作过程了，我们先为解析器定义一个BookParser接口，每种类型的解析器需要实现此接口。BookParser.java代码如下：

package com.scott.xml.parser;

import java.io.InputStream;
import java.util.List;

import com.scott.xml.model.Book;

public interface BookParser {
    /**
     * 解析输入流 得到Book对象集合
     * @param is
     * @return
     * @throws Exception
     */
    public List<Book> parse(InputStream is) throws Exception;

    /**
     * 序列化Book对象集合 得到XML形式的字符串
     * @param books
     * @return
     * @throws Exception
     */
    public String serialize(List<Book> books) throws Exception;
}

package com.scott.xml.parser; import java.io.InputStream; import java.util.List; import com.scott.xml.model.Book; public interface BookParser { /** * 解析输入流 得到Book对象集合 * @param is * @return * @throws Exception */ public List<Book> parse(InputStream is) throws Exception; /** * 序列化Book对象集合 得到XML形式的字符串 * @param books * @return * @throws Exception */ public String serialize(List<Book> books) throws Exception; }

好了，我们就该一个一个的实现该接口，完成我们的解析过程。

使用SAX解析器：

SaxBookParser.java代码如下：

package com.scott.xml.parser;

import java.io.InputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.DefaultHandler;

import com.scott.xml.model.Book;

public class SaxBookParser implements BookParser {

    @Override
    public List<Book> parse(InputStream is) throws Exception {
        SAXParserFactory factory = SAXParserFactory.newInstance();  //取得SAXParserFactory实例
        SAXParser parser = factory.newSAXParser();                  //从factory获取SAXParser实例
        MyHandler handler = new MyHandler();                        //实例化自定义Handler
        parser.parse(is, handler);                                  //根据自定义Handler规则解析输入流
        return handler.getBooks();
    }

    @Override
    public String serialize(List<Book> books) throws Exception {
        SAXTransformerFactory factory = (SAXTransformerFactory) TransformerFactory.newInstance();//取得SAXTransformerFactory实例
        TransformerHandler handler = factory.newTransformerHandler();           //从factory获取TransformerHandler实例
        Transformer transformer = handler.getTransformer();                     //从handler获取Transformer实例
        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");            // 设置输出采用的编码方式
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");                // 是否自动添加额外的空白
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");   // 是否忽略XML声明

        StringWriter writer = new StringWriter();
        Result result = new StreamResult(writer);
        handler.setResult(result);

        String uri = "";    //代表命名空间的URI 当URI无值时 须置为空字符串
        String localName = "";  //命名空间的本地名称(不包含前缀) 当没有进行命名空间处理时 须置为空字符串

        handler.startDocument();
        handler.startElement(uri, localName, "books", null);

        AttributesImpl attrs = new AttributesImpl();    //负责存放元素的属性信息
        char[] ch = null;
        for (Book book : books) {
            attrs.clear();  //清空属性列表
            attrs.addAttribute(uri, localName, "id", "string", String.valueOf(book.getId()));//添加一个名为id的属性(type影响不大,这里设为string)
            handler.startElement(uri, localName, "book", attrs);    //开始一个book元素 关联上面设定的id属性

            handler.startElement(uri, localName, "name", null); //开始一个name元素 没有属性
            ch = String.valueOf(book.getName()).toCharArray();
            handler.characters(ch, 0, ch.length);   //设置name元素的文本节点
            handler.endElement(uri, localName, "name");

            handler.startElement(uri, localName, "price", null);//开始一个price元素 没有属性
            ch = String.valueOf(book.getPrice()).toCharArray();
            handler.characters(ch, 0, ch.length);   //设置price元素的文本节点
            handler.endElement(uri, localName, "price");

            handler.endElement(uri, localName, "book");
        }
        handler.endElement(uri, localName, "books");
        handler.endDocument();

        return writer.toString();
    }

    //需要重写DefaultHandler的方法
    private class MyHandler extends DefaultHandler {

        private List<Book> books;
        private Book book;
        private StringBuilder builder;

        //返回解析后得到的Book对象集合
        public List<Book> getBooks() {
            return books;
        }

        @Override
        public void startDocument() throws SAXException {
            super.startDocument();
            books = new ArrayList<Book>();
            builder = new StringBuilder();
        }

        @Override
        public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
            super.startElement(uri, localName, qName, attributes);
            if (localName.equals("book")) {
                book = new Book();
            }
            builder.setLength(0);   //将字符长度设置为0 以便重新开始读取元素内的字符节点
        }

        @Override
        public void characters(char[] ch, int start, int length) throws SAXException {
            super.characters(ch, start, length);
            builder.append(ch, start, length);  //将读取的字符数组追加到builder中
        }

        @Override
        public void endElement(String uri, String localName, String qName) throws SAXException {
            super.endElement(uri, localName, qName);
            if (localName.equals("id")) {
                book.setId(Integer.parseInt(builder.toString()));
            } else if (localName.equals("name")) {
                book.setName(builder.toString());
            } else if (localName.equals("price")) {
                book.setPrice(Float.parseFloat(builder.toString()));
            } else if (localName.equals("book")) {
                books.add(book);
            }
        }
    }
}

package com.scott.xml.parser; import java.io.InputStream; import java.io.StringWriter; import java.util.ArrayList; import java.util.List; import javax.xml.parsers.SAXParser; import javax.xml.parsers.SAXParserFactory; import javax.xml.transform.OutputKeys; import javax.xml.transform.Result; import javax.xml.transform.Transformer; import javax.xml.transform.TransformerFactory; import javax.xml.transform.sax.SAXTransformerFactory; import javax.xml.transform.sax.TransformerHandler; import javax.xml.transform.stream.StreamResult; import org.xml.sax.Attributes; import org.xml.sax.SAXException; import org.xml.sax.helpers.AttributesImpl; import org.xml.sax.helpers.DefaultHandler; import com.scott.xml.model.Book; public class SaxBookParser implements BookParser { @Override public List<Book> parse(InputStream is) throws Exception { SAXParserFactory factory = SAXParserFactory.newInstance(); //取得SAXParserFactory实例 SAXParser parser = factory.newSAXParser(); //从factory获取SAXParser实例 MyHandler handler = new MyHandler(); //实例化自定义Handler parser.parse(is, handler); //根据自定义Handler规则解析输入流 return handler.getBooks(); } @Override public String serialize(List<Book> books) throws Exception { SAXTransformerFactory factory = (SAXTransformerFactory) TransformerFactory.newInstance();//取得SAXTransformerFactory实例 TransformerHandler handler = factory.newTransformerHandler(); //从factory获取TransformerHandler实例 Transformer transformer = handler.getTransformer(); //从handler获取Transformer实例 transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); // 设置输出采用的编码方式 transformer.setOutputProperty(OutputKeys.INDENT, "yes"); // 是否自动添加额外的空白 transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); // 是否忽略XML声明 StringWriter writer = new StringWriter(); Result result = new StreamResult(writer); handler.setResult(result); String uri = ""; //代表命名空间的URI 当URI无值时 须置为空字符串 String localName = ""; //命名空间的本地名称(不包含前缀) 当没有进行命名空间处理时 须置为空字符串 handler.startDocument(); handler.startElement(uri, localName, "books", null); AttributesImpl attrs = new AttributesImpl(); //负责存放元素的属性信息 char[] ch = null; for (Book book : books) { attrs.clear(); //清空属性列表 attrs.addAttribute(uri, localName, "id", "string", String.valueOf(book.getId()));//添加一个名为id的属性(type影响不大,这里设为string) handler.startElement(uri, localName, "book", attrs); //开始一个book元素 关联上面设定的id属性 handler.startElement(uri, localName, "name", null); //开始一个name元素 没有属性 ch = String.valueOf(book.getName()).toCharArray(); handler.characters(ch, 0, ch.length); //设置name元素的文本节点 handler.endElement(uri, localName, "name"); handler.startElement(uri, localName, "price", null);//开始一个price元素 没有属性 ch = String.valueOf(book.getPrice()).toCharArray(); handler.characters(ch, 0, ch.length); //设置price元素的文本节点 handler.endElement(uri, localName, "price"); handler.endElement(uri, localName, "book"); } handler.endElement(uri, localName, "books"); handler.endDocument(); return writer.toString(); } //需要重写DefaultHandler的方法 private class MyHandler extends DefaultHandler { private List<Book> books; private Book book; private StringBuilder builder; //返回解析后得到的Book对象集合 public List<Book> getBooks() { return books; } @Override public void startDocument() throws SAXException { super.startDocument(); books = new ArrayList<Book>(); builder = new StringBuilder(); } @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { super.startElement(uri, localName, qName, attributes); if (localName.equals("book")) { book = new Book(); } builder.setLength(0); //将字符长度设置为0 以便重新开始读取元素内的字符节点 } @Override public void characters(char[] ch, int start, int length) throws SAXException { super.characters(ch, start, length); builder.append(ch, start, length); //将读取的字符数组追加到builder中 } @Override public void endElement(String uri, String localName, String qName) throws SAXException { super.endElement(uri, localName, qName); if (localName.equals("id")) { book.setId(Integer.parseInt(builder.toString())); } else if (localName.equals("name")) { book.setName(builder.toString()); } else if (localName.equals("price")) { book.setPrice(Float.parseFloat(builder.toString())); } else if (localName.equals("book")) { books.add(book); } } } }

代码中，我们定义了自己的事件处理逻辑，重写了DefaultHandler的几个重要的事件方法。下面我为大家着重介绍一下DefaultHandler的相关知识。DefaultHandler是一个事件处理器，可以接收解析器报告的所有事件，处理所发现的数据。它实现了EntityResolver接口、DTDHandler接口、ErrorHandler接口和ContentHandler接口。这几个接口代表不同类型的事件处理器。我们着重介绍一下ContentHandler接口。结构如图：

这几个比较重要的方法已被我用红线标注，DefaultHandler实现了这些方法，但在方法体内没有做任何事情，因此我们在使用时必须覆写相关的方法。最重要的是startElement方法、characters方法和endElement方法。当执行文档时遇到起始节点，startElement方法将会被调用，我们可以获取起始节点相关信息；然后characters方法被调用，我们可以获取节点内的文本信息；最后endElement方法被调用，我们可以做收尾的相关操作。

最后，我们需要调用SAX解析程序，这个步骤在MainActivity中完成：

package com.scott.xml;

import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.List;

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 com.scott.xml.model.Book;
import com.scott.xml.parser.BookParser;
import com.scott.xml.parser.SaxBookParser;

public class MainActivity extends Activity {

    private static final String TAG = "XML";

    private BookParser parser;
    private List<Book> books;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button readBtn = (Button) findViewById(R.id.readBtn);
        Button writeBtn = (Button) findViewById(R.id.writeBtn);

        readBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    InputStream is = getAssets().open("books.xml");
                    parser = new SaxBookParser();  //创建SaxBookParser实例
                    books = parser.parse(is);  //解析输入流
                    for (Book book : books) {
                        Log.i(TAG, book.toString());
                    }
                } catch (Exception e) {
                    Log.e(TAG, e.getMessage());
                }
            }
        });
        writeBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    String xml = parser.serialize(books);  //序列化
                    FileOutputStream fos = openFileOutput("books.xml", Context.MODE_PRIVATE);
                    fos.write(xml.getBytes("UTF-8"));
                } catch (Exception e) {
                    Log.e(TAG, e.getMessage());
                }
            }
        });
    }
}

package com.scott.xml; import java.io.FileOutputStream; import java.io.InputStream; import java.util.List; 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 com.scott.xml.model.Book; import com.scott.xml.parser.BookParser; import com.scott.xml.parser.SaxBookParser; public class MainActivity extends Activity { private static final String TAG = "XML"; private BookParser parser; private List<Book> books; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Button readBtn = (Button) findViewById(R.id.readBtn); Button writeBtn = (Button) findViewById(R.id.writeBtn); readBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { try { InputStream is = getAssets().open("books.xml"); parser = new SaxBookParser(); //创建SaxBookParser实例 books = parser.parse(is); //解析输入流 for (Book book : books) { Log.i(TAG, book.toString()); } } catch (Exception e) { Log.e(TAG, e.getMessage()); } } }); writeBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { try { String xml = parser.serialize(books); //序列化 FileOutputStream fos = openFileOutput("books.xml", Context.MODE_PRIVATE); fos.write(xml.getBytes("UTF-8")); } catch (Exception e) { Log.e(TAG, e.getMessage()); } } }); } }

界面就两个按钮，顺便给大家贴上：

 

点击“readXML”按钮，将会调用SAX解析器解析文档，并在日志台打印相关信息：

然后再点击“writeXML”按钮，将会在该应用包下的files目录生成一个books.xml文件：

使用DOM解析器：

DomBookParser.java代码如下：

package com.scott.xml.parser;

import java.io.InputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
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 com.scott.xml.model.Book;

public class DomBookParser implements BookParser {

    @Override
    public List<Book> parse(InputStream is) throws Exception {
        List<Book> books = new ArrayList<Book>();
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  //取得DocumentBuilderFactory实例
        DocumentBuilder builder = factory.newDocumentBuilder(); //从factory获取DocumentBuilder实例
        Document doc = builder.parse(is);   //解析输入流 得到Document实例
        Element rootElement = doc.getDocumentElement();
        NodeList items = rootElement.getElementsByTagName("book");
        for (int i = 0; i < items.getLength(); i++) {
            Book book = new Book();
            Node item = items.item(i);
            NodeList properties = item.getChildNodes();
            for (int j = 0; j < properties.getLength(); j++) {
                Node property = properties.item(j);
                String nodeName = property.getNodeName();
                if (nodeName.equals("id")) {
                    book.setId(Integer.parseInt(property.getFirstChild().getNodeValue()));
                } else if (nodeName.equals("name")) {
                    book.setName(property.getFirstChild().getNodeValue());
                } else if (nodeName.equals("price")) {
                    book.setPrice(Float.parseFloat(property.getFirstChild().getNodeValue()));
                }
            }
            books.add(book);
        }
        return books;
    }

    @Override
    public String serialize(List<Book> books) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.newDocument();   //由builder创建新文档

        Element rootElement = doc.createElement("books");

        for (Book book : books) {
            Element bookElement = doc.createElement("book");
            bookElement.setAttribute("id", book.getId() + "");

            Element nameElement = doc.createElement("name");
            nameElement.setTextContent(book.getName());
            bookElement.appendChild(nameElement);

            Element priceElement = doc.createElement("price");
            priceElement.setTextContent(book.getPrice() + "");
            bookElement.appendChild(priceElement);

            rootElement.appendChild(bookElement);
        }

        doc.appendChild(rootElement);

        TransformerFactory transFactory = TransformerFactory.newInstance();//取得TransformerFactory实例
        Transformer transformer = transFactory.newTransformer();    //从transFactory获取Transformer实例
        transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");            // 设置输出采用的编码方式
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");                // 是否自动添加额外的空白
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");   // 是否忽略XML声明

        StringWriter writer = new StringWriter();

        Source source = new DOMSource(doc); //表明文档来源是doc
        Result result = new StreamResult(writer);//表明目标结果为writer
        transformer.transform(source, result);  //开始转换

        return writer.toString();
    }

}

package com.scott.xml.parser; import java.io.InputStream; import java.io.StringWriter; import java.util.ArrayList; import java.util.List; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.transform.OutputKeys; import javax.xml.transform.Result; import javax.xml.transform.Source; import javax.xml.transform.Transformer; 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 com.scott.xml.model.Book; public class DomBookParser implements BookParser { @Override public List<Book> parse(InputStream is) throws Exception { List<Book> books = new ArrayList<Book>(); DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); //取得DocumentBuilderFactory实例 DocumentBuilder builder = factory.newDocumentBuilder(); //从factory获取DocumentBuilder实例 Document doc = builder.parse(is); //解析输入流 得到Document实例 Element rootElement = doc.getDocumentElement(); NodeList items = rootElement.getElementsByTagName("book"); for (int i = 0; i < items.getLength(); i++) { Book book = new Book(); Node item = items.item(i); NodeList properties = item.getChildNodes(); for (int j = 0; j < properties.getLength(); j++) { Node property = properties.item(j); String nodeName = property.getNodeName(); if (nodeName.equals("id")) { book.setId(Integer.parseInt(property.getFirstChild().getNodeValue())); } else if (nodeName.equals("name")) { book.setName(property.getFirstChild().getNodeValue()); } else if (nodeName.equals("price")) { book.setPrice(Float.parseFloat(property.getFirstChild().getNodeValue())); } } books.add(book); } return books; } @Override public String serialize(List<Book> books) throws Exception { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.newDocument(); //由builder创建新文档 Element rootElement = doc.createElement("books"); for (Book book : books) { Element bookElement = doc.createElement("book"); bookElement.setAttribute("id", book.getId() + ""); Element nameElement = doc.createElement("name"); nameElement.setTextContent(book.getName()); bookElement.appendChild(nameElement); Element priceElement = doc.createElement("price"); priceElement.setTextContent(book.getPrice() + ""); bookElement.appendChild(priceElement); rootElement.appendChild(bookElement); } doc.appendChild(rootElement); TransformerFactory transFactory = TransformerFactory.newInstance();//取得TransformerFactory实例 Transformer transformer = transFactory.newTransformer(); //从transFactory获取Transformer实例 transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); // 设置输出采用的编码方式 transformer.setOutputProperty(OutputKeys.INDENT, "yes"); // 是否自动添加额外的空白 transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no"); // 是否忽略XML声明 StringWriter writer = new StringWriter(); Source source = new DOMSource(doc); //表明文档来源是doc Result result = new StreamResult(writer);//表明目标结果为writer transformer.transform(source, result); //开始转换 return writer.toString(); } }

然后再MainActivity中只需改一个地方：

 

     readBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
    try {
        InputStream is = getAssets().open("books.xml");
 //             parser = new SaxBookParser();
        parser = new DomBookParser();
        books = parser.parse(is);
        for (Book book : books) {
            Log.i(TAG, book.toString());
        }
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
    }
}
);

readBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { try { InputStream is = getAssets().open("books.xml"); // parser = new SaxBookParser(); parser = new DomBookParser(); books = parser.parse(is); for (Book book : books) { Log.i(TAG, book.toString()); } } catch (Exception e) { Log.e(TAG, e.getMessage()); } } });

执行结果是一样的。

使用PULL解析器：

PullBookParser.java代码如下：

package com.scott.xml.parser;

import java.io.InputStream;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.List;

import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlSerializer;

import android.util.Xml;

import com.scott.xml.model.Book;

public class PullBookParser implements BookParser {

    @Override
    public List<Book> parse(InputStream is) throws Exception {
        List<Book> books = null;
        Book book = null;

//      XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
//      XmlPullParser parser = factory.newPullParser();

        XmlPullParser parser = Xml.newPullParser(); //由android.util.Xml创建一个XmlPullParser实例
        parser.setInput(is, "UTF-8");               //设置输入流 并指明编码方式

        int eventType = parser.getEventType();
        while (eventType != XmlPullParser.END_DOCUMENT) {
            switch (eventType) {
            case XmlPullParser.START_DOCUMENT:
                books = new ArrayList<Book>();
                break;
            case XmlPullParser.START_TAG:
                if (parser.getName().equals("book")) {
                    book = new Book();
                } else if (parser.getName().equals("id")) {
                    eventType = parser.next();
                    book.setId(Integer.parseInt(parser.getText()));
                } else if (parser.getName().equals("name")) {
                    eventType = parser.next();
                    book.setName(parser.getText());
                } else if (parser.getName().equals("price")) {
                    eventType = parser.next();
                    book.setPrice(Float.parseFloat(parser.getText()));
                }
                break;
            case XmlPullParser.END_TAG:
                if (parser.getName().equals("book")) {
                    books.add(book);
                    book = null;
                }
                break;
            }
            eventType = parser.next();
        }
        return books;
    }

    @Override
    public String serialize(List<Book> books) throws Exception {
//      XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
//      XmlSerializer serializer = factory.newSerializer();

        XmlSerializer serializer = Xml.newSerializer(); //由android.util.Xml创建一个XmlSerializer实例
        StringWriter writer = new StringWriter();
        serializer.setOutput(writer);   //设置输出方向为writer
        serializer.startDocument("UTF-8", true);
        serializer.startTag("", "books");
        for (Book book : books) {
            serializer.startTag("", "book");
            serializer.attribute("", "id", book.getId() + "");

            serializer.startTag("", "name");
            serializer.text(book.getName());
            serializer.endTag("", "name");

            serializer.startTag("", "price");
            serializer.text(book.getPrice() + "");
            serializer.endTag("", "price");

            serializer.endTag("", "book");
        }
        serializer.endTag("", "books");
        serializer.endDocument();

        return writer.toString();
    }
}

package com.scott.xml.parser; import java.io.InputStream; import java.io.StringWriter; import java.util.ArrayList; import java.util.List; import org.xmlpull.v1.XmlPullParser; import org.xmlpull.v1.XmlSerializer; import android.util.Xml; import com.scott.xml.model.Book; public class PullBookParser implements BookParser { @Override public List<Book> parse(InputStream is) throws Exception { List<Book> books = null; Book book = null; // XmlPullParserFactory factory = XmlPullParserFactory.newInstance(); // XmlPullParser parser = factory.newPullParser(); XmlPullParser parser = Xml.newPullParser(); //由android.util.Xml创建一个XmlPullParser实例 parser.setInput(is, "UTF-8"); //设置输入流 并指明编码方式 int eventType = parser.getEventType(); while (eventType != XmlPullParser.END_DOCUMENT) { switch (eventType) { case XmlPullParser.START_DOCUMENT: books = new ArrayList<Book>(); break; case XmlPullParser.START_TAG: if (parser.getName().equals("book")) { book = new Book(); } else if (parser.getName().equals("id")) { eventType = parser.next(); book.setId(Integer.parseInt(parser.getText())); } else if (parser.getName().equals("name")) { eventType = parser.next(); book.setName(parser.getText()); } else if (parser.getName().equals("price")) { eventType = parser.next(); book.setPrice(Float.parseFloat(parser.getText())); } break; case XmlPullParser.END_TAG: if (parser.getName().equals("book")) { books.add(book); book = null; } break; } eventType = parser.next(); } return books; } @Override public String serialize(List<Book> books) throws Exception { // XmlPullParserFactory factory = XmlPullParserFactory.newInstance(); // XmlSerializer serializer = factory.newSerializer(); XmlSerializer serializer = Xml.newSerializer(); //由android.util.Xml创建一个XmlSerializer实例 StringWriter writer = new StringWriter(); serializer.setOutput(writer); //设置输出方向为writer serializer.startDocument("UTF-8", true); serializer.startTag("", "books"); for (Book book : books) { serializer.startTag("", "book"); serializer.attribute("", "id", book.getId() + ""); serializer.startTag("", "name"); serializer.text(book.getName()); serializer.endTag("", "name"); serializer.startTag("", "price"); serializer.text(book.getPrice() + ""); serializer.endTag("", "price"); serializer.endTag("", "book"); } serializer.endTag("", "books"); serializer.endDocument(); return writer.toString(); } }

然后再对MainActivity做以下更改：

        readBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    InputStream is = getAssets().open("books.xml");
//                  parser = new SaxBookParser();
//                  parser = new DomBookParser();
                    parser = new PullBookParser();
                    books = parser.parse(is);
                    for (Book book : books) {
                        Log.i(TAG, book.toString());
                    }
                } catch (Exception e) {
                    Log.e(TAG, e.getMessage());
                }
            }
        });

readBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { try { InputStream is = getAssets().open("books.xml"); // parser = new SaxBookParser(); // parser = new DomBookParser(); parser = new PullBookParser(); books = parser.parse(is); for (Book book : books) { Log.i(TAG, book.toString()); } } catch (Exception e) { Log.e(TAG, e.getMessage()); } } });

和其他两个执行结果都一样。

对于这三种解析器各有优点，我个人比较倾向于PULL解析器，因为SAX解析器操作起来太笨重，DOM不适合文档较大，内存较小的场景，唯有PULL轻巧灵活，速度快，占用内存小，使用非常顺手。读者也可以根据自己的喜好选择相应的解析技术