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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>
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;
- }
- }
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>
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 {
-
- public List<Book> parse(InputStream is) 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();
- SAXParser parser = factory.newSAXParser();
- MyHandler handler = new MyHandler();
- parser.parse(is, handler);
- return handler.getBooks();
- }
-
- @Override
- public String serialize(List<Book> books) throws Exception {
- SAXTransformerFactory factory = (SAXTransformerFactory) TransformerFactory.newInstance();
- TransformerHandler handler = factory.newTransformerHandler();
- Transformer transformer = handler.getTransformer();
- transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
- transformer.setOutputProperty(OutputKeys.INDENT, "yes");
- transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
-
- StringWriter writer = new StringWriter();
- Result result = new StreamResult(writer);
- handler.setResult(result);
-
- String uri = "";
- String localName = "";
-
- handler.startDocument();
- handler.startElement(uri, localName, "books", null);
-
- AttributesImpl attrs = new AttributesImpl();
- char[] ch = null;
- for (Book book : books) {
- attrs.clear();
- attrs.addAttribute(uri, localName, "id", "string", String.valueOf(book.getId()));
- handler.startElement(uri, localName, "book", attrs);
-
- handler.startElement(uri, localName, "name", null);
- ch = String.valueOf(book.getName()).toCharArray();
- handler.characters(ch, 0, ch.length);
- handler.endElement(uri, localName, "name");
-
- handler.startElement(uri, localName, "price", null);
- ch = String.valueOf(book.getPrice()).toCharArray();
- handler.characters(ch, 0, ch.length);
- handler.endElement(uri, localName, "price");
-
- handler.endElement(uri, localName, "book");
- }
- handler.endElement(uri, localName, "books");
- handler.endDocument();
-
- return writer.toString();
- }
-
-
- private class MyHandler extends DefaultHandler {
-
- private List<Book> books;
- private Book book;
- private StringBuilder builder;
-
-
- 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);
- }
-
- @Override
- public void characters(char[] ch, int start, int length) throws SAXException {
- super.characters(ch, start, length);
- builder.append(ch, start, length);
- }
-
- @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();
- books = parser.parse(is);
- 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);
- 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();
- DocumentBuilder builder = factory.newDocumentBuilder();
- Document doc = builder.parse(is);
- 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();
-
- 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();
- Transformer transformer = transFactory.newTransformer();
- transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
- transformer.setOutputProperty(OutputKeys.INDENT, "yes");
- transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
-
- StringWriter writer = new StringWriter();
-
- Source source = new DOMSource(doc);
- Result result = new StreamResult(writer);
- transformer.transform(source, result);
-
- 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 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;
-
-
- XmlPullParser parser = Xml.newPullParser();
- parser.setInput(is, "UTF-8");
-
- 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 {
-
- XmlSerializer serializer = Xml.newSerializer();
- StringWriter writer = new StringWriter();
- serializer.setOutput(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 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。
Android中解析XML
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原文地址:http://www.cnblogs.com/liuchaogege/p/4567236.html