AJAX实践之与服务器通信(1)


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 " ,serv

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