??? XML寫法比較簡單，而且非常便于人來閱讀。但是必須在客戶端和服務(wù)器端有XML的解析器才可以正常通信，由于初期的移動信息設(shè)備內(nèi)存和處理器上的不足，所以在MIDP1.0中并沒有提供對XML的支持。隨著內(nèi)存和處理器的提高，對XML的支持成為了可能。在JSR182中提供了XML的解析器，但是這并不是標準MIDP中的API需要特定的實現(xiàn)才可以支持。幸運的是有第三方的API對解析xml提供了支持，比較有名的是kxml和nanoxml。

??? 使用XML之前，你必須考慮好是不是必須用它來傳輸數(shù)據(jù)，因為解析xml是比較耗費資源的，尤其是在CPU和內(nèi)存的資源都很寶貴的條件下。如果我們能使用DataInputStream和DataOutputStream傳輸?shù)脑捑捅M量不要使用XML。XML的解析器有兩種，一種是確認性的，他在解析之前會對xml的文檔進行有效性的驗證，確保這是應(yīng)用程序需要的。另一種則是非確認性的，他不做驗證工作直接進行解析，無疑這樣的速度會快。kxml和nanoxml都是這樣的解析器。它們也存在差別，kxml是增量解析器他會一點一點的解析，這樣在解析大的文檔的時候會效率比較高。nanoxml是一步解析器，一次就把文檔解析完，如果文檔很大的話，這無疑會耗費很大的內(nèi)存。要使用kxml你可以從http://www.kxml.org 下載得到,在http://nanoxml.sourceforge.net?你可以下載nanoxml。

??? 要使用kxml，你必須首先得到一個XmlParser實例，它用Reader作為構(gòu)造器的參數(shù)：
try {
??? Reader??? r = .....;
??? XmlParser parser = new XmlParser( r );
}
catch( java.io.IOException e ){
??? // handle exception....
}

如果你的xml文檔存儲在String內(nèi)的話你可以使用ByteArrayInputStream和InputStreamReader：
String??? xml = "<a>some xml</a>";
ByteArrayInputStream bin =
??????????? new ByteArrayInputStream( xml.getBytes() );
XmlParser parser = new XmlParser( new InputStreamReader( bin ) );
當(dāng)從網(wǎng)上接收數(shù)據(jù)的時候可以這樣：
HttpConnection??? conn = .....;
InputStreamReader doc =
???????? new InputStreamReader( conn.openInputStream() );
XmlParser parser = new XmlParser( doc );
得到parser實例后我們就可以調(diào)用read方法進行解析了，read方法會返回一個ParseEvent,通過判斷他的類型我們就可以解析xml了。
try {
??? boolean keepParsing = true;
???????
??? while( keepParsing ){
??????? ParseEvent event = parser.read();
?
??????? switch( event.getType() ){
??????????? case Xml.START_TAG:
??????????????? ..... // handle start of an XML tag
??????????????? break;
??????????? case Xml.END_TAG:
??????????????? ..... // handle end of an XML tag
??????????????? break;
??????????? case Xml.TEXT:
??????????????? ..... // handle text within a tag
??????????????? break;
??????????? case Xml.WHITESPACE:
??????????????? ..... // handle whitespace
??????????????? break;
??????????? case Xml.COMMENT:
??????????????? ..... // handle comment
??????????????? break;
??????????? case Xml.PROCESSING_INSTRUCTION:
??????????????? ..... // handle XML PI
??????????????? break;
??????????? case Xml.DOCTYPE:
??????????????? ..... // handle XML doctype
??????????????? break;
??????????? case Xml.END_DOCUMENT:
??????????????? ..... // end of document;
??????????????? keepParsing = false;
??????????????? break;
??????? }
??? }
}
catch( java.io.IOException e ){
}

如果想使用nanoxml，那么你首先要創(chuàng)建一個kXMLElement實例，然后調(diào)用parseFromReader、parseString或者parseCharArray。由于他是一步解析器，那么它會把整個文檔解析完后生成一個Object tree。每個節(jié)點都是一個kXMLElement的實例，通過調(diào)用getChildren等方法可以在這棵樹上導(dǎo)航。
HttpConnection??? conn = .....;
InputStreamReader doc =
???????? new InputStreamReader( conn.openInputStream() );
kXMLElement?????? root = new kXMLElement();

try {
??? root.parseFromReader( doc );
}
catch( kXMLParseException pe ){
}
catch( IOException ie ){
}

下面是一個J2ME的應(yīng)用程序簡單演示了如何解析xml。如果有時間可以寫寫復(fù)雜的測試程序。你可以從如下地址下載源代碼：XMLTest. 里面包括了kxml和nanoxml的源代碼，如果想得到最新的源代碼請參考他們的官方網(wǎng)站，在本站提供了kxml的在線API
package com.ericgiguere.techtips;

import java.io.*;
import java.util.*;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;
import nanoxml.*;
import org.kxml.*;
import org.kxml.parser.*;

/**
?* Simple MIDlet that demonstrates how an XML document can be
?* parsed using kXML or NanoXML.
?*/

public class XMLTest extends MIDlet {

??? // Our XML document -- normally this would be something you
??? // download.
???
??? private static String xmlDocument =
??????? "<list><item>apple</item>" +
????????????? "<item>orange</item>" +
????????????? "<item>pear</item></list>";
?????????????
??? private Display display;
??? private Command exitCommand = new Command( "Exit",
?????????????????????????????????????????????? Command.EXIT, 1 );
??????????????????????????????????????????????
??? public XMLTest(){
??? }
???
??? protected void destroyApp( boolean unconditional )
?????????????????????? throws MIDletStateChangeException {
??????? exitMIDlet();
??? }
???
??? protected void pauseApp(){
??? }
???
??? protected void startApp() throws MIDletStateChangeException {
??????? if( display == null ){ // first time called...
??????????? initMIDlet();
??????? }
??? }
???
??? private void initMIDlet(){
??????? display = Display.getDisplay( this );
???????
??????? String [] items;
???????
??????? //items = parseUsingNanoXML( xmlDocument );
??????? items = parseUsingkXML( xmlDocument );
???????
??????? display.setCurrent( new ItemList( items ) );
??? }
???
??? public void exitMIDlet(){
??????? notifyDestroyed();
??? }
???
??? // Parses a document using NanoXML, looking for
??? // "item" nodes and returning their content as an
??? // array of strings.
???
??? private String[] parseUsingNanoXML( String xml ){
??????? kXMLElement root = new kXMLElement();
??????? try {
??????????? root.parseString( xml );
???????????
??????????? Vector list = root.getChildren();
??????????? Vector items = new Vector();
???????????
??????????? for( int i = 0; i < list.size(); ++i ){
??????????????? kXMLElement node =
???????????????????? (kXMLElement) list.elementAt( i );
??????????????? String????? tag = node.getTagName();
???????????????
??????????????? if( tag == null ) continue;
??????????????? if( !tag.equals( "item" ) ) continue;
???????????????
??????????????? items.addElement( node.getContents() );
??????????? }
???????????
??????????? String[] tmp = new String[ items.size() ];
??????????? items.copyInto( tmp );
??????????? return tmp;
??????? }
??????? catch( kXMLParseException ke ){
??????????? return new String[]{ ke.toString() };
??????? }
??? }
???
??? // Parses a document using kXML, looking for "item"
??? // nodes and returning their content as an
??? // array of strings.
???
??? private String[] parseUsingkXML( String xml ){
??????? try {
??????????? ByteArrayInputStream bin =
??????????????????????????? new ByteArrayInputStream(
???????????????????????????????????? xml.getBytes() );
??????????? InputStreamReader in = new InputStreamReader( bin );
??????????? XmlParser parser = new XmlParser( in );
??????????? Vector??? items = new Vector();
???????????
??????????? parsekXMLItems( parser, items );
???????????
??????????? String[] tmp = new String[ items.size() ];
??????????? items.copyInto( tmp );
??????????? return tmp;
??????? }
??????? catch( IOException e ){
??????????? return new String[]{ e.toString() };
??????? }
??? }
???
??? private void parsekXMLItems( XmlParser parser, Vector items )
???????????????????????????????????? throws IOException {
??????? boolean inItem = false;
???????
??????? while( true ){
??????????? ParseEvent event = parser.read();
??????????? switch( event.getType() ){
??????????????? case Xml.START_TAG:
??????????????????? if( event.getName().equals( "item" ) ){
??????????????????????? inItem = true;
??????????????????? }
??????????????????? break;
??????????????? case Xml.END_TAG:
??????????????????? if( event.getName().equals( "item" ) ){
??????????????????????? inItem = false;
??????????????????? }
??????????????????? break;
??????????????? case Xml.TEXT:
??????????????????? if( inItem ){
??????????????????????? items.addElement( event.getText() );
??????????????????? }
??????????????????? break;
??????????????? case Xml.END_DOCUMENT:
??????????????????? return;
??????????? }
??????? }
??? }
???
??? // Simple List UI component for displaying the list of
??? // items parsed from the XML document.
???
??? class ItemList extends List implements CommandListener {
???
??????? ItemList( String[] list ){
??????????? super( "Items", IMPLICIT, list, null );
??????????? addCommand( exitCommand );
??????????? setCommandListener( this );
??????? }
???????
??????? public void commandAction( Command c, Displayable d ){
??????????? if( c == exitCommand ){
??????????????? exitMIDlet();
??????????? }
??????? }
??? }
}