We Keep Coding

How does the Spring forms .jsp tag library work?

So I have a .jsp page which has a form on it, like this (naturally this is a massive simplification):
<form:form commandName="myCommand" method="post">
<form:select path="values" class="select-tall" multiple="multiple" id="mySelect">
<option>first</option>
<option>second</option>
<option>third</option>
</form:select>
<button type="submit" class="button">Save</button>
</form:form>
When the submit button is pressed, the form is submitted(somehow) and the path= attributes are used to bind the data inside the form elements to the properties of an instance of a plain old java object. I understand how this POJO is specified, and I understand how the POST request is routed to the correct controller, but I don't understand where or how the form values are mapped to the given POJO.
What I don't understand is:
How does the spring tag library modify the form such that this binding takes place?
How would one go about doing this in a manual or ad-hoc fashion(using a Javascript onSubmit() method, say)?
Essentially my question is: How does the spring-form.tld tag library work?
Any resources, or even a high-level explanation in your own words, would be extremely helpful.
I've implemented a work-around solution in the mean time (dynamically adding items to a hidden form element), but I feel like this is hack-y and the wrong solution.

Mule: Http->xml

Mule version: 3,5 (Actually, mule studio)
I'm new at using mule and can't seem to figure out how to do the following properly:
Want to achieve:
Send data from a html form to mule which then splits the payload and sends one part to one java program and the other to another.
Html form:
<form method="GET" action="http://localhost:8081">
<input type="text" name="name"/>
<input type="text" name="lastname"/>
<input type="submit" value="Submit" />
</form>
This points to localhost and the port which is set in MuleStudio.
Real Question:
What could I use to transform the data from the inbound http to xml?
Side Question:
I can send the whole payload to one javaprogram. (first a POJO and then to the actual program. - is this the right way or can I send it to the program and skipping the POJO?)

Since your main concern is about transformation, let's only address it.
If you're using the Enterprise Edition, you can use DataMapper to generate the XML you need. Creating a schema representing the target XML would help a lot.
Otherwise, if you're using the Community Edition, you can use different options:
A Groovy component using the excellent MarkupBuilder to generate the target XML right from the inbound message payload,
A chain of standard transformers that first transform the submitted data to a generic XML form (object-to-xml-transformer) then transform it to the desired form (xslt-transformer).
I'm sure there are other options, but these should get you going :)

Spring validation framework multiple model attributes error message not displayed on jsp

I am trying to validate 2 model attributes on one action using spring validation framework. The purpose is to validate the lookUpbean (search criterion) on click of Search button and then to validate the resultant bean also i.e memberShipbean once we get it from the services so that we can show warnings to the user if some fields are empty in the resultant bean.
<form:form method="POST" modelAttribute="lookupPageBean" id="lookupForm" name="lookupForm"
action="lookupMembership.htm">
<td class="error">
<form:errors path="membershipNumber" />
<form:input class="medium-textbox" id="membershipNumber" path="membershipNumber" />
<button type="submit" class="Active-button-small">
<fmt:message key="button.go" />
</button>`
#RequestMapping(method = RequestMethod.POST, value = URLMappingConstant.MEMBERSHIP_LOOKUP)
public String viewMembership(ModelMap modelMap, HttpServletRequest request, HttpServletResponse response,
#ModelAttribute(UIConstant.LOOKUP_PAGE_BEAN) LookupPageBean lookupPageBean, BindingResult result,
#ModelAttribute(UIConstant.MEMBERSHIP_BEAN) MembershipPageBean membershipPageBean, BindingResult error) throws WebMTracksException
{
membershipValidator.validate(lookupPageBean, result);
membershipValidator.validate(membershipPageBean, error);
}
Now what is happening is first validation is working fine however during second validation
the error messages are not shown on the resultant jsp ,
however the errors are reported till this controller layer in the “error” binding results.
Also in the validation layer
ValidationUtils.rejectIfEmpty(errors, UIConstant.BUSINESSNAME,ValidationMSGConstants.BUSINESS_NAME)
This method always returns validation errors even if the field is not empty.
First question is can we have multiple model attributes in one action. I read it somewhere on internet but could not find any implementation of the same. Please help me to resolve this issue. Also let me know if you can think of any other working solution for this problem but I would like to use only the spring framework for the both the validations as that helps to maintain the existing design of the application.

I do not think you have bind multiple Model Attributes to the same form, which I believe is what you are asking. I am not even sure what that request would look like, from an HTTP stand point, as I don't believe Spring would have a way to detangle all the bean's properties, especially if the names overlap. What you may want to consider doing is wrapping your LookupPageBean and MembershipPageBean into one "form bean".
As for the error messages, you may want to take a look at the spring:bind tag. It may do what you are needed to get the binding errors from the second Model Attribute.

How do I send data between servlets?

I am pretty new to servlets and web development in general.
So basically I have a servlet that queries a database and returns some values, like a name. What I want is to turn the name into a link that opens a details page for that name (which another servlet would handle). How can I send the name to the other servlet so it can query a database for the relevant details?
Maybe I'm taking the wrong approach?
Edit: I am using Tomcat 5.5

Pass it as request parameter.
Either add it to the query string of the URL of the link to the other servlet which is then available by request.getParameter("name") in the doGet() method.
link
Or add it as a hidden input field in a POST form which submits to the other servlet which is then available by request.getParameter("name") in the doPost() method.
<form action="otherservlet" method="post">
<input type="hidden" name="name" value="${name}" />
<input type="submit" />
</form>
See also:
Servlets info page - contains a Hello World

Not sure if I understand correctly, but you may look at javax.servlet.RequestDispatcher and forward the url to the second servlet.
The url could be created using the name:
http://myhost.mydomain/my.context/servlet2.do?name=John

I would create the URL either in the first servlet or in a client using a configurable template for the URL. This way both servlets are clearly separated - you can even have each one on different machine.

Cross-site tomcat form post not working

For a customer, I need to write a Servlet which can print values in a form post. The form is hosted on another server and looks somewhat like this:
<form action="http://myserver/myServlet" method="POST">
<input type="text" id="someName" value="someInterestingValue"/>
<input type="submit" value="submit" />
</form>
I have a Tomcat 5.0.28 server available, running on a Java 1.4 jdk, so I made a simple servlet:
public class ProxyServlet extends HttpServlet {
public void doPost(HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException {
PrintWriter out = res.getWriter();
Enumeration a =req.getAttributeNames();
while (a.hasMoreElements()){
String attrname = (String) a.nextElement();
out.println(attrname+"="+req.getAttribute(attrname)+"<br/>");
}
out.close();
}
}
When I go to the servlet by URL everything looks as expected. When I send a GET request with some parameters, I can see those as attributes in the debugger in the doGet() method (method was left out for brevety).
However, in the doPost(), my form fields seem to be missing. I've looked into the Tomcat logfiles, and nothing special is logged. I tried to add a crossdomain.xml to some directories but did not find a way to change this behaviour.
So to be clear: The Form as listed above is on server A. My servlet runs on an existing legacy Tomcat/Java application hosted on server B. When the form is of type "POST" none of the fields arrive at the Servlet on server B. Apache is NOT "in front" of Tomcat.
Is there some configuration setting I am missing in Tomcat?
Any tips or suggestions where to look next?
Help is greatly appreciated.

Request attributes? Don't you need to access them as request parameters using HttpServletRequest#getParameter() and so on?
Which adds more confusion is that you said that it works in the doGet(). How does its code look like then? Does it also access them as attributes? That would in a normal JSP/Servlet environment (i.e. you aren't using some filter which copies the parameters to attributes or so) have been impossible.

This has nothing to do with cross-site. As BalusC said, use getParameter... instead of getAttribute... methods

Found the problem. After a whole day of searching and coding, it all boils down to the fact that my code was working fine. The problem is in the form. the line:
<input type="text" id="someName" value="someInterestingValue"/>
Should read:
<input type="text" name="someName" value="someInterestingValue"/>
For people mentioning "getParameter" instead of "getAttribute" you are totally correct. In my test code I had both just to be sure (because I thought I lost it...) but both were not returning results, as the browser was simply not sending the name/value pairs.
I guess posting this on Stackoverflow did help, because I had to explain and re-read my problem I thought the "id=" looked funny. Coding is finding bugs in pieces of text you are overlooking...