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Javascript changes dissapear when going back from servlet to JSP

Good evening,
I have a form on a JSP page that's connected to a servlet, that form has some dynamic parts using JavaScript like adding a row to a table or adding a text field based on the selected option on a select element, Actually my problem is that I have some validations on the servlet-side, so when I go to servlet to check the (National ID) for example if there's any problem or any violations to my validation I force to get back to the form using :
if (dbm.MatchIdNumber(Candidate.getRegNumber(), Candidate.getNationalID()) == false) {
out.println("<script>\n"
+ " alert('Your National Id does not match your Registration Number');\n"
+ "</script>");
out.println("<script>\n"
+ " window.history.go(-1);\n"
+ "</script>");
}
What happens is when I get back to the form I lose all the JavaScript changes, Which's very important.
I've been reading for a while that using ajax might be the optimal solution for me, but here is my questions:
Is there a way to call a java method from JavaScript or JQuery before getting to servlet without using ajax !?!
Is there a way to get back from the servlet to the jsp page with the ability to keep all the JavaScript Chages !?
If not !!, How to use ajax in my case ?!
Thank you so much

No. JavaScript runs on the user's browser and your Java code runs on your webserver, so basically the only way to communicate between the two is via HTTP requests.
If you don't want to use AJAX, you could provide all of the relevant info when you submit the form to the server for validation. You could pass all the info you need to re-generate the form as it was, like which new fields are there and such
First, you'll need to add a new webservice to your Java webapp which performs validation. To achieve this, you could either add additional logic to your servlet (so that it looks for a request parameter like "doValidation=1" and performs validation if it's there) or write a different servlet that handles validation itself. You'll need to decide the format it should expect the form data in and how it should return the validation information.
On your frontend page, you'll need to modify the behavior of the form so that, when you need to do validation, it performs a request to this webservice and passes along the form data. I would probably do this with jQuery and do something like jQuery.ajax(...) and pass the contents of the form as a JSON object.
When your validation servlet returns data from the ajax call, you'll need to update the form based on the data it provides. If I was doing it, I would probably just have the servlet return a JSON object like {errorMessage:"..."} and I would use jQuery to add an element to the form containing the text of the validation error when it occurs. If the servlet returns an empty string or JSON object or something, I would consider it a validation success.

Sending a String in Javascript to java method in Play Framework

I'm working on a system for my university and I'm using the play framework to do that.
The Admin of this system sets a marker on a google map and I get the coordinates from that point.
Now I'm trying to pass this information to the server side, so that I might store these to Strings in a mySQL database. The only problem I have is passing the data from my String in javascript/JQuery to the java function.
I tried different solutions on the internet but some of them seemed outdated and I couldn't figure out how to do it.
I've only been programming in Java, Javascript, JQuery and PHP and have never used AJAX (like the $.get() methode from JQuery), but I think it might be pretty similar to what I know from PHP.
e.g.
http://java.dzone.com/articles/jquery-ajax-play-2
I'd like to pass my String with a button click to my java function, so I can store it in my db.
I'm really confused about this.
I know I can use something like
<a href="{#routes.Application.postMethod()}"> Send </>
and then mention the function in the routes like
POST /post controllers.Application.post();
but how do I pass my qjuery string?
and how do I store my String as a String in a java function like:
public static Result post(String Lat, String Lng){
???????????? EVOLUTION NEEDED ?????
}
Thanks in advance I really need your help :)!

I don't see why you are doing a POST, since this can be done using a GET request.
As per this example:
http://www.playframework.com/documentation/1.2/ajax#jsaction
We can see Play makes it easier using the jsAction tag. Lets assume you have the following route:
GET /admins/marker Admins.marker
Then in your HTML, at the bottom you'd do something like:
<script type="text/javascript">
$('#myButton').click( function() {
var action = #{jsAction #marker(':latitude',':longitude') /}
$('#result').load(
action({latitude: '23', longitude: $('#longitudeField').val }),
function() {
$('#content').css('visibility', 'visible')
}
)
});
</script>
In this case, the request will be sent like (example):
GET /admins/marker?latitude=23&longitude=67
And then on your backend, you need the have to java fn to deal with that route.
Basically the javascript/jquery, is called when #myButton element is clicked, then we generate the route URL we are going to make a request to using jsAction, then we make using load to make a GET request. You can change this to post too if you'd like.

how to forward back to JSP page without losing the data entered in fields?

I have a simple MVC-based JSP application. Something like:
*.jsp -> ControllerServlet -> *Command.java -> *Service.java -> *DAO.java -> Oracle db
A typical link in the application looks like this:
myapp/controller?cmd=ShowEditUser&userid=55
Which causes ShowEditUserCommand.java execute() method to run and will forward to editUser.jsp
In editUser.jsp, they fill in the fields, then click Save which posts to myapp/controller?cmd=ModifyUser which runs ModifyUserCommand.java execute() method which modifies the user data and forwards to viewUser.jsp.
Everything works fine.
The problem is, in ModifyUserCommand.execute() I'm checking to see if the username is unique. If they try to enter a username that already exists, I set an error value to true and errorMessage value to Already in use.
Then because of the error I forward to the original editUser.jsp (not viewUser.jsp) and the error is displayed above the form.
MY PROBLEM IS (finally! ;) -- when the user is returned to editUser.jsp with the error message displayed, the data they entered in the fields is all blanked out. How can I set it so whatever they entered in the fields is still in place?
Any suggestions or advice are greatly appreciated!
Rob

Simplest way would be to pass the form fields back to your editUser.jsp in your forward action in ModifyUserCommand.execute(). You can do that with individual parameters i.e.
editUser.jsp?field1=1&field2=2
Alternatively, you could pass data with other methods - i.e. encoded JSON.
You can then process your fields in your editUser.jsp via the page's request object and set your form field values accordingly.
There may be other ways to do this depending on what underlying framework (if any) you are using. But this is a basic way of approaching it.

wicket: mapping different paths to the same class on request to generate different content in markup

I developed a shopsystem. there is a product page, which lists the available items filtered by some select menus. there is also one item detail page to view some content about each product. the content of that page will be loaded out of an xml property file. if one would click the link in the listview of an item, to view some details, an item specific GET parameter is set. with the parameters value, i can dynamically load the content for that specific item from my properties, by altering the loaded keys name.
so far so good, but not really good. so much to the backgroud. lets get to some details.
most of all, this is some SEO motivated stuff. so far there is also a problem with the pageinstance Id in the url for statefull pages, not only because of the nonstable url, also because wicket is doing 302 redirects to manipulate the url. maybe I will remove the statefull components of the item detailpage to solve that problem.
so now there are some QR-code on the products being sold, that contain a link to my detail page. these links are not designed by myself and as you can imagine, they look a whole lot of different like the actual url. lets say the QR-code url path would be "/shop/item1" where item1 would be the product name. my page class would be ItemDetailPage .
I wrote an IRequestMapper that I am mounting in my WebApplication#init() that is resolving the incoming requests URL and checks wether it needs to be resolved by this IRequestMapper. If so, I build my page with PageProvider and return a requesthandler for it.
public IRequestHandler mapRequest(Request request) {
if(compatibilityScore>0) {
PageProvider provider = new PageProvider(ItemDetailPage.class, new ItemIDUrlParam(request.getUrl().getPath().split("/")[1]));
provider.setPageSource(Application.get().getMapperContext());
return new RenderPageRequestHandler(provider);
}
return null;
}
So as you can see, I build up a parameter that my detailpage can handle. But the resulting URL is not very nice. I'd like to keep the original url by mapping the bookmarkable content to it, without any redirect.
My first thought was to implement an URLCodingStrategy to rebuild the URL with its parameters in the form of a path. I think the HybridUrlCodingStrategy is doing something like that.
After resolving the URL path "/shop/item1/" with the IRequestMapper it would look like "/shop/item?1?id=item1" where the first parameter off course is the wicket pageinstance Id, which will most likely be removed as I will rebuild the detail page to be stateless :(
after applying an HybridURLCodingStrategy it might look like "/shop/item/1/id/item1" or "/shop/item/id/item1" without pageinstance Id. another Idea would be to remove the second path part and the parameter name and only use the parameters value so the url would look like "/shop/item1" which is then the same url as it was in the request.
Do you guys have any experience with that or any smart ideas?
The rewuirements are
Having one fix URL for each product the SE bot can index
no parameters
stateless and bookmarkable
no 302 redirects in any way.
the identity of the requested item must be available for the detailpage
with kind regards from germany
Marcel

As Bert stated, your use case should be covered with normal page mounting, see also the MountedMapper wiki page, for your case a concrete example:
mountPage("/shop/${id}", ShopDetailPage.class);
Given that "item1" is the ID of the item (which is not very clear to me), you can retrieve it now as the named page parameter id in Wicket. Another example often seen in SEO links, containing both the unique ID and the (non-unique, changing) title:
mountPage("/shop/${id}/${title}", ShopDetailPage.class);
Regarding the page instance ID, there are some ways to get rid of it, perhaps the best way is to make the page stateless as you said, another easy way is to configure IRequestCycleSettings.RenderStrategy.ONE_PASS_RENDER as the render strategy (see API doc for consequences).

selecting pulldown in htmlunit

I am using htmlunit in jython and am having trouble selecting a pull down link. The page I am going to has a table with other ajax links, and I can click on them and move around and it seems okay but I can't seem to figure out how to click on a pulldown menu that allows for more links on the page(this pulldown affects the ajax table so its not redirecting me or anything).
Here's my code:
selectField1 = page.getElementById("pageNumSelection")
options2 = selectField1.getOptions()
theOption3 = options2[4]
This gets the option I want, I verify its right. so I select it:
MoreOnPage = selectField1.setSelectedAttribute(theOption3, True)
and I am stuck here(not sure if selecting it works or not because I don't get any message, but I'm not sure what to do next. How do I refresh the page to see the larger list? When clicking on links all you have to do is find the link and then select linkNameVariable.click() into a variable and it works. but I'm not sure how to refresh a pulldown. when I try to use the webclient to create an xml page based on the the select variable, I still get the old page.
to make it a bit easier, I used htmlunit scripter and got some code that should work but its java and I'm not sure how to port it to jython. Here it is:
try
{
page = webClient.getPage( url );
HtmlSelect selectField1 = (HtmlSelect) page.getElementById("pageNumSelection");
List<HtmlOption> options2 = selectField1.getOptions();
HtmlOption theOption3 = null;
for(HtmlOption option: options2)
{
if(option.getText().equals("100") )
{
theOption3 = option;
break;
}
}
selectField1.setSelectedAttribute(theOption3, true );

Have a look at HtmlForm getSelectedByName
HtmlSelect htmlSelect = form.getSelectByName("stuff[1].type");
HtmlOption htmlOption = htmlSelect.getOption(3);
htmlOption.setSelected(true);

Be sure that WebClient.setJavaScriptEnabled is called. The documentation seems to indicate that it is on by default, but I think this is wrong.
Alternatively, you can use WebDriver, which is a framework that supports both HtmlUnit and Selenium. I personally find the syntax easier to deal with than HtmlUnit.

If I understand correctly, the selection of an option in the select box triggers an AJAX calls which, once finished, modifies some part of the page.
The problem here is that since AJAX is, by definition, asynchronous, you can't really know when the call is finished and when you may inspect the page again to find the new content.
HtmlUnit has a class named NicelyResynchronizingAjaxController, which you can pass an instance of to the WebClient's setAjaxController method. As indicated in the javadoc, using this ajax controller will automatically make the asynchronous calls coming from a direct user interaction synchronous instead of asynchronous. Once the setSelectedAttribute method is called, you'll thus be able to see the changed made to the original page.
The other option is to use WebClient's waitForBackgrounfJavascript method after the selection is done, and inspect he page once the background JavaScript has ended, or the timeout has been reached.

This isn't really an answer to the question because I've not used HtmlUnit much before, but you might want to look at Selenium, and in particular Selenium RC. With Selenium RC you are able to control the interactions with a page displayed in a native browser (Firefox for example). It has developer API's for Java and Python amongst others.
I understand that HtmlUnit uses its own javascript and web browser rendering engine and I'm wondering whether that may be a problem.