1、SAX解析XML文件
在Android平台上可以使用Simple API for XML(SAX) 、 Document Object Model(DOM)和Android附带的pull解析器解析XML文件。 下面是本例子要解析的XML文件:
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leo.xml<?xml version="1.0" encoding="UTF-8"?> <persons> <person id="23"> <name>李明</name> <age>30</age> </person> <person id="20"> <name>李向梅</name> <age>25</age> </person> </persons>
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解析过程解析leo.xml触发的事件为: 读到的标签及内容 触发事件 {文档开始} startDocument() <persons> startElement(, "persons", null, "{Attributes}") "\n\t" characters("<persons>...</persons>", "12", "2") <person> startElement(, "person", null, "{Attributes}") "\n\t\t" characters("<persons>...</persons>", "31", "3") <name> startElement(, "name", null, "{Attributes}") "李明" characters("<persons>...</persons>", "40", "2") </name> endElement(" ", "name", null) "\n\t\t" characters("<persons>...</persons>", "50", "3") <age> startElement(, "age", null, "{Attributes}") "30" characters("<persons>...</persons>", "58", "2") </age> endElement("", "age", null) "\n\t" characters("<persons>...</persons>", "67", "2") </person> endElement("", "person", null) "\n\t" characters("<persons>...</persons>", "79", "2") <person> startElement(, "person", null, "{Attributes}") "\n\t\t" characters("<persons>...</persons>", "98", "3") <name> startElement(, "name", null, "{Attributes}") "李向梅" characters("<persons>...</persons>", "107", "3") </name> endElement("", "name", null) "\n\t\t" characters("<persons>...</persons>", "118", "3") <age> startElement(, "age", null, "{Attributes}") "25" characters("<persons>...</persons>", "126", "2") </age> endElement("", "age", null) "\n\t" characters("<persons>...</persons>", "135", "2") </person> endElement("", "person", null) "\n" characters("<persons>...</persons>", "147", "1") </persons> endElement("", "persons", null) {文档结束} endDocument()
SAX是一个解析速度快并且占用内存少的xml解析器,非常适合用于Android等移动设备。 SAX解析XML文件采用的是事件驱动,也就是说,它并不需要解析完整个文档,在按内容顺序解析文档的过程中,SAX会判断当前读到的字符是否合法XML语法中的某部分,如果符合就会触发事件。所谓事件,其实就是一些回调(callback)方法,这些方法(事件)定义在ContentHandler接口。下面是一些ContentHandler接口常用的方法:
startDocument()
当遇到文档的开头的时候,调用这个方法,可以在其中做一些预处理的工作。
endDocument()
和上面的方法相对应,当文档结束的时候,调用这个方法,可以在其中做一些善后的工作。
startElement(String namespaceURI, String localName, String qName, Attributes atts)
当读到一个开始标签的时候,会触发这个方法。namespaceURI就是命名空间,localName是不带命名空间前缀的标签名,qName是带命名空间前缀的标签名。通过atts可以得到所有的属性名和相应的值。要注意的是SAX中一个重要的特点就是它的流式处理,当遇到一个标签的时候,它并不会纪录下以前所碰到的标签,也就是说,在startElement()方法中,所有你所知道的信息,就是标签的名字和属性,至于标签的嵌套结构,上层标签的名字,是否有子元属等等其它与结构相关的信息,都是不得而知的,都需要你的程序来完成。这使得SAX在编程处理上没有DOM来得那么方便。
endElement(String uri, String localName, String name)
这个方法和上面的方法相对应,在遇到结束标签的时候,调用这个方法。
characters(char[] ch, int start, int length)
这个方法用来处理在XML文件中读到的内容,第一个参数用于存放文件的内容,后面两个参数是读到的字符串在这个数组中的起始位置和长度,使用new String(ch,start,length)就可以获取内容。
只要为SAX提供实现ContentHandler接口的类,那么该类就可以得到通知事件(实际上就是SAX调用了该类中的回调方法)。因为ContentHandler是一个接口,在使用的时候可能会有些不方便,因此,SAX还为其制定了一个Helper类:DefaultHandler,它实现了这个接口,但是其所有的方法体都为空,在实现的时候,你只需要继承这个类,然后重载相应的方法即可。
文件结构如下:
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Person.javapackage com.leo.domain; public class Person { private Integer id; private String name; private Short age; public Person(){} public Person(String name, Short age) { this.name = name; this.age = age; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Short getAge() { return age; } public void setAge(Short age) { this.age = age; } @Override public String toString() { return "id="+id+",name="+name+",age="+age; } }
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SAXPersonService.javapackage com.leo.service; import java.io.InputStream; import java.util.List; import javax.xml.parsers.SAXParser; import javax.xml.parsers.SAXParserFactory; import com.leo.domain.Person; public class SAXPersonService { public static List<Person> readXml(InputStream inStream) throws Exception { SAXParserFactory spf = SAXParserFactory.newInstance(); SAXParser saxParser = spf.newSAXParser(); //创建解析器 XMLContentHandler handler = new XMLContentHandler(); saxParser.parse(inStream, handler); inStream.close(); return handler.getPersons(); } }
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XMLContentHandler.javapackage com.leo.service; import java.util.ArrayList; import java.util.List; import org.xml.sax.Attributes; import org.xml.sax.SAXException; import org.xml.sax.helpers.DefaultHandler; import com.leo.domain.Person; public class XMLContentHandler extends DefaultHandler { private List<Person> persons; private Person person; private String preTag; public List<Person> getPersons() { return persons; } /* * 接收文档的开始的通知。 */ @Override public void startDocument() throws SAXException { persons = new ArrayList<Person>(); } /* * 接收字符数据的通知。 */ @Override public void characters(char[] ch, int start, int length) throws SAXException { if(person!=null){ String data = new String(ch,start,length); if("name".equals(preTag)){ person.setName(data); }else if ("age".equals(preTag)){ person.setAge(new Short(data)); } } } /* * 接收元素开始的通知。 */ @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { if("person".equals(localName)){ person = new Person(); person.setId(new Integer(attributes.getValue("", "id"))); } preTag = localName; } /* * 接收文档的结尾的通知。 */ @Override public void endElement(String uri, String localName, String qName) throws SAXException { if("person".equals(localName)&&person!=null){ persons.add(person); person = null; } preTag = null; } }
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SAXPersonServiceTest.javapackage com.leo.xml; import java.io.InputStream; import java.util.List; import android.test.AndroidTestCase; import android.util.Log; import com.leo.domain.Person; import com.leo.service.SAXPersonService; public class SAXPersonServiceTest extends AndroidTestCase { private static final String TAG = "SAXPersonServiceTest"; public void testReadXml() throws Exception{ InputStream inStream = SAXPersonServiceTest.class.getClassLoader().getResourceAsStream("leo.xml"); List<Person> persons = SAXPersonService.readXml(inStream); for( Person person : persons){ Log.i(TAG, person.toString()); } } }
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XMLActivity.javapackage com.leo.xml; import java.io.InputStream; import java.util.List; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.widget.TextView; import android.widget.Toast; import com.leo.domain.Person; import com.leo.service.SAXPersonService; public class XMLActivity extends Activity { private static final String TAG = "XMLActivity"; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView resultView = (TextView)this.findViewById(R.id.result); InputStream inStream = XMLActivity.class.getClassLoader().getResourceAsStream("leo.xml"); try { List<Person> persons = SAXPersonService.readXml(inStream); StringBuilder sb = new StringBuilder(); for(Person person : persons){ sb.append(person.toString()).append("\n"); } resultView.setText(sb.toString()); } catch (Exception e) { Log.e(TAG, e.toString()); Toast.makeText(this, "XML解析失败", Toast.LENGTH_LONG).show(); } } }
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mail.xml<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" android:id="@+id/result" /> </LinearLayout>
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strings.xml<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, XMLActivity!</string> <string name="app_name">xml解析器</string> </resources>
2、DOM解析XML文件
在com.leo.service添加:
DOMPersonService.javapackage com.leo.service; 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; import org.w3c.dom.Element; import org.w3c.dom.Node; import org.w3c.dom.NodeList; import com.leo.domain.Person; public class DOMPersonService { public static List<Person> readXml(InputStream inStream) throws Exception { List<Person> persons = new ArrayList<Person>(); /*InputStream 也可以是网络,或者文件*/ DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); /*以树状格式,存储在内存中;比较耗费内存*/ Document document = builder.parse(inStream); Element root = document.getDocumentElement(); /*得到person的节点列表*/ NodeList nodes = root.getElementsByTagName("person"); for(int i=0; i < nodes.getLength(); i++){ Element personElement = (Element)nodes.item(i);//element /text == node Person person = new Person(); person.setId(new Integer(personElement.getAttribute("id"))); /*得到子节点*/ NodeList childnodes = personElement.getChildNodes(); for(int j=0; j<childnodes.getLength(); j++ ){ Node childNode = (Node)childnodes.item(j); if(childNode.getNodeType() == Node.ELEMENT_NODE){ Element childElement = (Element)childNode; if("name".equals(childElement.getNodeName())){ person.setName(childElement.getFirstChild().getNodeValue()); } else if("age".equals(childElement.getNodeName())){ person.setAge(new Short(childElement.getFirstChild().getNodeValue())); } } } persons.add(person); } return persons; } }
在XmlPersonServiceTest.java添加如下代码:
XmlPersonServiceTest.javapackage com.leo.xml; import java.io.InputStream; import java.util.List; import android.test.AndroidTestCase; import android.util.Log; import com.leo.domain.Person; import com.leo.service.DOMPersonService; import com.leo.service.SAXPersonService; public class XmlPersonServiceTest extends AndroidTestCase { private static final String TAG = "XmlPersonServiceTest"; /*使用SAX解析xml*/ public void testSAXReadXml() throws Exception{ InputStream inStream = XmlPersonServiceTest.class.getClassLoader().getResourceAsStream("leo.xml"); List<Person> persons = SAXPersonService.readXml(inStream); for( Person person : persons){ Log.i(TAG, person.toString()); } } /*使用DOM解析xml内容,适合于解析比较小的xml内容*/ public void testDOMReadXml() throws Exception{ InputStream inStream = XmlPersonServiceTest.class.getClassLoader().getResourceAsStream("leo.xml"); List<Person> persons = DOMPersonService.readXml(inStream); for( Person person : persons){ Log.i(TAG, person.toString()); } } }