HFSJ EL-Functions mock question doubt

[Adam Czysciak]

Hi everyone,

I'm going through HFSJ... Page 431, question 14, on EL functions:

package com.example;
public class MyFunctions {
  public static String repeat(int x, String str ) {
    // ethod body
  }
}

JSP:
1. <@ taglib uri="/WEB-INF/myfuncts" prefix="my" %?
2. <%- insert code here -->

Which, inserted at line 2 in the JSP, is a valid EL function invocation
A. $(repeat(2, "420")}
B. $(repeat("2", "420")}
C. $(my:repeat(2, "420")}
D. $(my:repeat("2", "420")}
E. A valid invocation CANNOT be determined

The correct answer is E with explanation "Option E is correct. The necessary mapping information is NOT known."

My question is - why is it not know? If we assume that there exists a proper .tld file, then isn't C the correct invocation? Of course A and B are incorrect, as "my" prefix is required.

And what about D? Aren't EL functions arguments coerced the way they do in EL expressions?

[Reshma Shanbhag]

I tried to implement this example, the app throws with the following exception ..

org.apache.jasper.JasperException: The class int i specified in the method signature in TLD for the function dice:voilaDice cannot be found. int i
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:510)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:375)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

I am not sure if am doing anything wrong ... the class is definition is a..

package com.scwcd.elfunction;
 
public class RollDice {


public static int rollDice(int i, java.lang.String s){
System.out.println(" Executing the ROLL DICE FUNCTIONALITY .. Received Input Values : " + i + ", " + s);
return (int) ((Math.random()*6) + 1 );
}
 
}

and the TLD declaration is as follows ..

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
  <a href="http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"" target="_blank" rel="nofollow">http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"</a>
  version="2.0">
 
<tlib-version>1.0</tlib-version>
<short-name>diceRoller</short-name>
<uri>diceRoller</uri>
<function>
   <name>voilaDice</name>
   <function-class>com.scwcd.elfunction.RollDice</function-class>
   <function-signature>
              int rollDice(int i, java.lang.String s)
           </function-signature>
</function>
</taglib>

and the jsp invocation with the taglib directive included in the page is:

<%@taglib uri="/tags/diceRoller" prefix="dice"%>
 
The rollDice value is : ${dice:voilaDice("1", "Reshma")}
 <br/>
The rollDice value is : ${dice:voilaDice(1, "Reshma")}

Why is the Servlet container looking for a int class ... rather than considering it as a primitive ??? when i execute this example without the method parameter it works fine .. am i doing anything wrong ???




Reshma

[Reshma Shanbhag]

Got the answer to my post ...


The function signature in the TLD must only have type's in parameter list and not the variable identifiers .. that was the mistake !!

it must be

<function-signature>
           int rollDice(int, java.lang.String )
      </function-signature>

and not

<function-signature>
           int rollDice(int i, java.lang.String s)
      </function-signature>

Coming to the Orignal Post..

If the proper TLD was in place option C & D (arguments are coerced) would have been correct options.

In book option E is selected, as there is no mention (no TLD) of the name "repeat" is to be used to invoke the tag. So as the TLD in not available we cannot determine valid invocation, hence E is the right option from the given Choices.


Hope this helps,

Reshma

[Bryan Basham]

My question is - why is it not know? If we assume that there exists a proper .tld file, then isn't C the correct invocation? Of course A and B are incorrect, as "my" prefix is required.

Actually, it is the fact that the question does not specify the TLD for this EL function, that makes Option E the only valid option.

Remember that a certification question must be self-contained. You are not allowed to make any assumptions; unless the question itself tells you to assume something.

Does that make sense?

Cheers,
Bryan

[Reshma Shanbhag]

Thanks for clarifying Bryan ... that makes it very clear

[Adam Czysciak]

Thanks Bryan. That explains everything. So it is just like I though - I need to read the questions carefully and not to assume anything
[ May 25, 2006: Message edited by: Adam Czysciak ]