dropdown-ajax

Here you go, this is I wrote for my jsp:

//create XMLHttpRequest object

function getHTTPObject() {

var xmlhttp;

if (window.XMLHttpRequest) // if Mozilla, Safari etc

xmlhttp = new XMLHttpRequest();

else if (window.ActiveXObject){ // if IE

try {

xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");

}

catch ( e ){

try{

xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");

}

catch ( e ){}

}

}

return xmlhttp;

}

var httpObject = getHTTPObject(); //global variable

function getSecondListValues() {

var URL = "getValues.do"; //have action mappings in struts-config.xml

var selectedVal = '';

var selObj = document.getElementById('<fisrt combo box name here>');

var selIndex = document.getElementById('<fisrt combo box name here>').selectedIndex;

selectedVal = selObj.options[selIndex].text;

var queryString = "selectedVal="+escape(selectedVal);

httpObject.open( "Post", URL, true );

httpObject.onreadystatechange = attrResponse;

httpObject.setRequestHeader( "Content-Type", "application/x-www-form-urlencoded" );

httpObject.send(queryString);

}

function attrResponse() {

if (httpObject.readyState == 4)

{

if (httpObject.status == 200)

{

var getVal = httpObject.responseText; //gets all the output values from the action class

var valarray=getVal.split(",");

for (var i=0; i < valarray.length;++i){

addOption(document.getElementById("<second combo box name here>"), valarray[i], valarray[i]);

}

}

}

}

}

function trim(stringToTrim) {

return stringToTrim.replace(/^\s+|\s+$/g,"");

}

function addOption(selectbox,text,value)

{

var optn = document.createElement("OPTION");

optn.text = trim(text);

optn.value = trim(value);

selectbox.options.add(optn);

}

//use this fn to clear values in the second select, when first select values changes

function removeAllOptions(selectbox)

{

var i;

for(i=selectbox.options.length-1;i>=0;i--)

{

selectbox.remove(i);

}

}

//your action class should be something like below:

public class GetAttributeValuesAction extends Action

{

public ActionForward execute(ActionMapping mapping, ActionForm form,

HttpServletRequest request, HttpServletResponse response)

throws Exception {

String forward = "success";

String selectedVal = request.getParameter("selectedVal"); //get the first select value

HttpSession session = request.getSession( true );

ActionErrors errors = new ActionErrors();

String value = null;

try {

if(selectedval != null )

{

ArrayList val = new ArrayList();

//use your logic and get the second select values

//comma seperated

for( int i = 0; i < val.size(); i++)

{

if( i == 0)

{

value = val.get(i);

}

else

{

value = value + "," + val.get(i);

}

}

}

} catch (Exception e) {

}

PrintWriter out = response.getWriter();

out.println(value);

// Finish with

return null;

}

skp71a at 2007-7-28 15:42:52 >

I have only worked using struts and MVC model. When you want to use AJAX (dynamically interacting), why should the page reload?

skp71a at 2007-7-28 15:42:52 >

The whole point of using Ajax is that you DON'T refresh the entire JSP page.

You only load some extra info, and then use javascript to modify the page in place - in your case change the options which appear on your list.

If you want to reload the entire page, then you don't use Ajax.

evnafetsa at 2007-7-28 15:42:52 >

>but in the source code above when we use struts we should return >ActionForward which leads to the destination to which the controller, might be

>directed to perform a RequestDispatcher.forward

That is the normal pattern in struts. Most cases you send a request (click a button/link) and you want an HTML page in response to replace the one currently in the browser window.

But AJAX is different. You still want to send a request and get a response, but you want to leave the current page as is. For that you use the javascript HTTPRequest component. In this case the response wanted is not an HTML page, but just a comma separated list of values to put in the select box.

This struts action is different. It doesn't return an actionForward. Instead the action returns null, which informs struts that "I have taken care of the response thank you very much, you don't need to do anything".

This action has taken care of the response itself (sending a comma separated list of values) and doesn't need or want Struts to do anything else.

In this case, the response is a comma separated list of values.

The response gets sent back to the javascript HTTPRequest component.

That then calls the javascript function attrResponse which gets the comma separated value list, and uses it to populate the select box using javascript.

You have send a request, got a response, but the page didn't have to reload - it just used javascript to modify the existing page.

Hope this helps,

evnafets

evnafetsa at 2007-7-28 15:42:52 >

Hello All,

Thank you for your replies.I'm following a framework that follows MVC

I have my dopost() as:

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws IOException, ServletException {

try {

boolean istrue = false;

//I'll put the response in session

istrue = doAction(request);

if(istrue) {

RequestDispatcher requestDispatcher = request.getRequestDispatcher(nextPage);

requestDispatcher.forward(request,response);

}

else

//error page

}

}

And in my doAction() that I have to implement at the end of the method I have something like this:

HttpServletResponse response = (HttpServletResponse) mySession.getAttribute("response");

PrintWriter out = response.getWriter();

out.println(value);

istrue = true;

So, my Question is after the doAction() return true the dopost() forwards the request to the next URL so are we really reloading the whole jsp again...I'm I doing it correctly ?

Help is greatly appreciated.

Thanks...

Greeshma12a at 2007-7-28 15:42:52 >