Standard Tags, Design Pattern Qs

[lalit upadheyay]

Hi All,

I have some doubts on design patterns and JSP standard tags. I got curious about some standard tags after going through the JSTL spec. Please do reply to following doubts

Design Pattern:
1. Is Intercepting filter a Presentation tier or Business Tier Pattern ?
2. How is struts related to MVC and front controller pattern ?

Standard Tags (please refer to JSTL spec ):
1. How can i iterate over key and value sets returned through keySet() and entrySet() methods of following map in a <c:forEach > tag :

<%
java.util.Map capitalMap=new java.util.HashMap();
capitalMap.put("Punjab","Chandigarh");
capitalMap.put("Haryana","Chandigarh");
capitalMap.put("Orissa","Bhubneshwar");
capitalMap.put("Bihar","Patna");
capitalMap.put("Maharastra","Mumbai");
capitalMap.put("Tamil Nadu","Chennai");
request.setAttribute("MyStateMap",capitalMap);
%>

2. What is the use of var attribute in <c:if> tag ? Please give a simple example?

3. In the JSTL spec., var attribute of <c:forEach > tag has been mentioned as optional in both the syntaxes. So how can i access value of current item in a List without specifying var attribute ?

Regards,
[ December 01, 2005: Message edited by: lalit upadheyay ]

[Marc Peabody]

Design Pattern:
1. Is Intercepting filter a Presentation tier or Business Tier Pattern ?
* If you learn what those three terms mean, it will be very obvious.
2. How is struts related to MVC and front controller pattern ?
* Struts is a framework that boasts both but I don't think it's important for the test.

Standard Tags (please refer to JSTL spec ):
1. How can i iterate over key and value sets returned through keySet() and entrySet() methods of following map in a <c:forEach > tag :
<%
java.util.Map capitalMap=new java.util.HashMap();
capitalMap.put("Punjab","Chandigarh");
capitalMap.put("Haryana","Chandigarh");
capitalMap.put("Orissa","Bhubneshwar");
capitalMap.put("Bihar","Patna");
capitalMap.put("Maharastra","Mumbai");
capitalMap.put("Tamil Nadu","Chennai");
request.setAttribute("MyStateMap",capitalMap);
%>
*I believe you can specify .key and .value on your iterated items.

2. What is the use of var attribute in <c:if> tag ? Please give a simple example?
* var here will be a Boolean that represents the evaluation of the test attribute

3. In the JSTL spec., var attribute of <c:forEach > tag has been mentioned as optional in both the syntaxes. So how can i access value of current item in a List without specifying var attribute ?
* I don't think you can. You should only leave out var if you don't need access to the objects:
<c:forEach start="1" end="10">
I'm displaying this 10 times.
</c:forEach>

[Christophe Verré]

About the Standard Tags:

1.
<c:forEach items="${MyStateMap}" var="statemap">
<c ut value="${statemap.key},${statemap.value}"/>
</c:forEach>

2. <c:if> is mainly used to output something in certain condition

<c:if test="${isSunny}">
What a beautiful day !
</c:if>


3. Var is optional because you can use forEach as a simple loop.
If you want to iterate through a List, you'll have to use var.

[rohit lodha]

Design Pattern:
1. Is Intercepting filter a Presentation tier or Business Tier Pattern ?
2. How is struts related to MVC and front controller pattern ?

----------------------------------------------------------------
answer

intercepting filter ---------- presentation tier
struts related to front controller

[Umakanth Godavarthy]

Almost all the questions are answered, just wanted to add one more thing on importance of 'var' attrib in <c:if>.
If you see there is another attrib 'scope', if these two attributes are combined, you can access the result of this particular expr as any other scoped attribute that has a Boolean type.

[lalit upadheyay]

Hi guys,

Thanks for your reply but regarding Q 1 on Standard tags , i want output like

keyset:
===========
Punjab
Haryana
Orissa
Bihar
Maharastra
Tamil Nadu

entryset:
===========
Chandigarh
Chandigarh
Bhubneshwar
Patna
Mumbai
Chennai

I want the output in two separate loops (non nested) , one following the other using EL's or stands tags.

Sorry for being unable to put my question earlier exactly.

Thanks and Regards

[Christophe Verré]

I suppose that what you call entries mean values of the map.
The you should do the same loop twice :

  
keyset:<br>
===========<br>
<c:forEach items="${MyStateMap}" var="statemap">
   <c:out value="${statemap.key}"/><br>
</c:forEach>
<br>
entryset:<br>
===========<br>
<c:forEach items="${MyStateMap}" var="statemap">
   <c:out value="${statemap.value}"/><br>
</c:forEach>

[ December 06, 2005: Message edited by: Satou kurinosuke ]

[ December 06, 2005: Message edited by: Satou kurinosuke ]
[ December 06, 2005: Message edited by: Satou kurinosuke ]