AJAX編程實踐之與服務器通信-ShareBody資訊站

AJAX編程實踐之與服務器通信

首先看下看下相對簡單些的--向服務器發送一個包含有名/值對的簡單查詢串，在這種情況下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/值對的參數形式了（如name=LiLin&age=23）,在調用OPEN方法中，當請求方法是用POST的時候為了確保服務器知道請求體中有請求參數，需要調用setRequestHeader，將Content-Type值設置為application/x-www-form-urlencoded.當然也可不放在請求體中（那就不要用POST啦！）

此時server處理：

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 " );
}
}

對get and post方法都用processRequest來處理。

要向服務器發送相關復雜的查詢串，可以將模型變化為XML發送到server 。

client端:

createXML方法無非就是將內容以DOM的樣式存到var xml（變量）里。有時也可能出現client直接將本地的一個XML文件直接以DOM（當然可以edit）的樣式傳送.(也放這個時個的Content-Type應該為text/xml了!)這時可能要用到ActiveXObject("MSXML2.DOMDocument.3.0")這樣一個控件了。

關于這個控件有個方法可以在各broswer中通用的JS代碼：

// --------------------------------------------------------------------
// 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);

當然也可以直接從server取來（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);
}
}
}

實際上xmlDoc.loadXML(xmlht.responseText)所得到的就是一個于內存中的DOM了,而直接用responseXML的話就直接可以解析為一個DOM了!(注意load（FILE）與loadXML（DOM）是不同的)

此時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(); i ++ ) {
type = selectedPetTypes.item(i).getFirstChild().getNodeValue();
responseText = responseText + " " + type;
}

response.setContentType( " text/xml " );
response.getWriter().print(responseText);
}

private String readXMLFromRequestBody(HttpServletRequest request) {
StringBuffer xml = new StringBuffer();
String line = null ;
try {
BufferedReader reader = request.getReader();
while ((line = reader.readLine()) != null ) {
xml.append(line);
}
}
catch (Exception e) {
System.out.println( " Error reading XML: " + e.toString());
}
return xml.toString();
}
}

DOM,JDOM,JAXP隨便你自己選好了！

作者：http://www.zhujiangroad.com

來源：http://www.zhujiangroad.com

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