首先看下看下相对简单些的--向服务器发送一个包含有名/值对的简单查询串，在这种情况下XHP即可以用GET也可以用POST。
GET
function doRequestUsingGET() {
createXMLHttpRequest();
var queryString = " GetAndPostExample? " ;
queryString = queryString + createQueryString()+ " &timeStamp= " + new Date().getTime();
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.open( " GET " , queryString, true );
xmlHttp.send( null );
}
POST
function doRequestUsingPOST() {
createXMLHttpRequest();
var url = " GetAndPostExample?timeStamp= " + new Date().getTime();
var queryString = createQueryString();
xmlHttp.open( " POST " , url, true );
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.setRequestHeader( " Content-Type " , " application/x-www-form-urlencoded " );
xmlHttp.send(queryString);
}
queryString就是名/值对的参数形式了（如name=LiLin&age=23）,在调用OPEN方法中，当请求方法是用POST的时候为了确保服务器知道请求体中有请求参数，需要调用setRequestHeader，将Content-Type值设置为application/x-www-form-urlencoded.当然也可不放在请求体中（那就不要用POST啦！）
此时server处理：
import java.io. * ;
import java.net. * ;
import javax.servlet. * ;
import javax.servlet.http. * ;
public class GetAndPostExample extends HttpServlet {
protected void processRequest(HttpServletRequest request, HttpServletResponse response, String method)
throws ServletException, IOException {
// Set content type of the response to text/xml
response.setContentType( " text/xml " );
// Get the user's input
String firstName = request.getParameter( " firstName " );
String middleName = request.getParameter( " middleName " );
String birthday = request.getParameter( " birthday " );
// Create the response text
String responseText = " Hello " + firstName + " " + middleName
+ " . Your birthday is " + birthday + " . "
+ " [Method: " + method + " ] " ;
// Write the response back to the browser
PrintWriter out = response.getWriter();
out.println(responseText);
// Close the writer
out.close();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Process the request in method processRequest
processRequest(request, response, " GET " );
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Process the request in method processRequest
processRequest(request, response, " POST " );
}
}
对get and post方法都用processRequest来处理。
要向服务器发送相关复杂的查询串，可以将模型变化为XML发送到server 。
client端:
function createXML() {
var xml = " <pets> " ;
var options = document.getElementById( " petTypes " ).childNodes;
var option = null ;
for ( var i = 0 ; i < options.length; i ++ ) {
option = options[i];
if (option.selected) {
xml = xml + " <type> " + option.value + " <\/type> " ;
}
}
xml = xml + " <\/pets> " ;
return xml;
}
function sendPetTypes() {
createXMLHttpRequest();
var xml = createXML();
var url = " PostingXMLExample?timeStamp= " + new Date().getTime();
xmlHttp.open( " POST " , url, true );
xmlHttp.onreadystatechange = handleStateChange;
xmlHttp.setRequestHeader( " Content-Type " , " application/x-www-form-urlencoded " );
xmlHttp.send(xml);
}
createXML方法无非就是将内容以DOM的样式存到var xml（变量）里。有时也可能出现client直接将本地的一个XML文件直接以DOM（当然可以edit）的样式传送.(也放这个时个的Content-Type应该为text/xml了!)这时可能要用到ActiveXObject("MSXML2.DOMDocument.3.0")这样一个控件了。
关于这个控件有个方法可以在各broswer中通用的JS代码：
// --------------------------------------------------------------------
// Function: CreateXMLDOM
//
// Purpose: Creates a new XML DOM.
//
// Parameters: None
//
// Returns: XMLDOM object OR null
// --------------------------------------------------------------------
function CreateXmlDOM()
{
var oXML = new ActiveXObject(GetXmlParserProgID());
try
{
oXML.setProperty( " AllowXsltScript " , true );
}
catch (err) {}
oXML.async = false ;
oXML.validateOnParse = false ;
oXML.resolveExternals = false ;
oXML.setProperty( " SelectionLanguage " , " XPath " );
try {oXML.setProperty( " NewParser " , true );} catch (e) {}
return oXML;
}
// ----------------------------------------------------
// Function: GetXmlParserProgID
//
// Purpose:
// Gets the ProgID of the highest available version of the
// Microsoft XML parser.
//
// Parameters: None
//
// Returns: String (i.e. "Msxml2.DOMDocument.4.0")
//
// ----------------------------------------------------
function GetXmlParserProgID()
{
var MAX_MAJOR_PARSER_VERSION = 10 ;
var MIN_MAJOR_PARSER_VERSION = 0 ;
var MAX_MINOR_PARSER_VERSION = 9 ;
var MIN_MINOR_PARSER_VERSION = 0 ;
var sProgID = g_sXmlParserProgID;
var bFound = false ;
if ( ! sProgID)
{
// Iterate through possible versions
for ( var nMajor = MAX_MAJOR_PARSER_VERSION; nMajor >= MIN_MAJOR_PARSER_VERSION; nMajor -- )
{
for ( var nMinor = MAX_MINOR_PARSER_VERSION; nMinor >= MIN_MINOR_PARSER_VERSION; nMinor -- )
{
// Set up the classname for the version that we're trying to instantiate
sProgID = " Msxml2.DOMDocument. " + nMajor + " . " + nMinor;
try
{
if ( new ActiveXObject(sProgID))
{
bFound = true ;
break ;
}
}
catch (e)
{}
}
if (bFound)
{
// store in a global variable to speedup subsequent calls
g_sXmlParserProgID = sProgID;
break ;
}
}
}
return sProgID;
}
然后直接用其load方法（本地）。
var xmlDoc = new ActiveXObject( " MSXML2.DOMDocument.3.0 " );
xmlDoc.load(local_XML_FileName);
当然也可以直接从server取来（用get方法即可），然后以responseText的方法
xmlht.Open( " GET " ,server_XML_FileName, true );
xmlht.onreadystatechange = stateChange;
xmlht.Send( null );
function handleStateChange() {
if (xmlHttp.readyState == 4 ) {
if (xmlHttp.status == 200 ) {
xmlDoc.loadXML(xmlht.responseText);
}
}
}
实际上xmlDoc.loadXML(xmlht.responseText)所得到的就是一个于内存中的DOM了,而直接用responseXML的话就直接可以解析为一个DOM了!(注意load（FILE）与loadXML（DOM）是不同的)
此时servert process :
import java.io. * ;
import javax.servlet. * ;
import javax.servlet.http. * ;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
public class PostingXMLExample extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String xml = readXMLFromRequestBody(request);
Document xmlDoc = null ;
try {
xmlDoc =
DocumentBuilderFactory.newInstance().newDocumentBuilder()
.parse( new ByteArrayInputStream(xml.getBytes()));
}
catch (ParserConfigurationException e) {
System.out.println( " ParserConfigurationException: " + e);
}
catch (SAXException e) {
System.out.println( " SAXException: " + e);
}
/**/ /* Note how the Java implementation of the W3C DOM has the same methods
* as the JavaScript implementation, such as getElementsByTagName and
* getNodeValue.
*/
NodeList selectedPetTypes = xmlDoc.getElementsByTagName( " type " );
String type = null ;
String responseText = " Selected Pets: " ;
for ( int i = 0 ; i < selectedPetTypes.getLength();
