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Page 8 of 8
5. Implementation of JSTL Function
Tags
Now,
let�s have a look at the JSTL Function tag. Create a new JSP. Let�s name it
Jstl_Functions_Tags.jsp. Then create a new link to direct to this new JSP.
<table
border="1">
<tr>
<td>
<a href="Jstl_Functions_Tags.jsp">JSTL Functions Tags</a>
</td>
<td>
String
Manipulations
</td>
</tr>
</table>
Do not forget to include JSTL taglib
directive for prefix fn in our JSP. Here is how to import the fn JSTL taglib
directive.
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions"
prefix="fn" %>
The JSTL functions tag will mainly deal with string manipulation.
Let�s try some of them.
<c:set
var="sentence" value=" Try This String for Manipulations "
/>
<c:out
value="${sentence}" />
Above codes are used to set a fixed string to variable �sentence� and
print it out for display. Next, please pay attention on how we are going to combine
JSTL core <c> tag with JSTL function <fn> tag.
<c:out
value="${fn:length(sentence)}" />
Above codes will print out the length of variable �sentence�. It will
produce 35 since all characters are counted.
<c:out
value="${fn:toUpperCase(sentence)}" />
<c:out
value="${fn:toLowerCase(sentence)}" />
Above codes are used to convert our �sentence� to UPPER or LOWER case.
<c:out
value="${fn:trim(sentence)}" />
<c:out
value="${fn:length(fn:trim(sentence))}" />
<c:out
value="${fn:replace(sentence,' ','_')}" />
Above codes are used to trim the �sentence� and count the length of
trimmed �sentence�. Trimming the sentence means that we are removing the extra
spaces (if any) in the string either in front or in back. You need to know that
the spaces within the string will NOT be trimmed. It should produce 33 since
the spaces at the beginning and at the end will be discarded. While the sample
above of fn:replace will replace all occurrences of spaces with underscores.
<c:out
value="${fn:substring(sentence,0,8)}" />
<c:out
value="${fn:substringAfter(sentence,'for')}" />
<c:out
value="${fn:substringBefore(sentence,'for')}" />
<c:out
value="${fn:indexOf(sentence,'g')}" />
The fn:substring will take 3 parameters. 1st parameter is
our �sentence� variable itself. 2nd parameter is for the starting
point and 3rd parameter is where it must stop to return result of
substring. More advanced substring functions are fn:substringAfter and fn:substringBefore.
See at the screenshot to see how they work.
And the fn:indexOf will return the position of defined character in
our �sentence�.
<c:out
value="${fn:contains(sentence,'G')}" />
<c:out
value="${fn:containsIgnoreCase(sentence,'G')}" />
<c:out
value="${fn:startsWith(sentence,' Try')}" />
<c:out
value="${fn:endsWith(sentence,'pulations ')}" />
fn:contains will return boolean value true if correct and false
otherwise. However, it is case sensitive and will sensitively check for the
lower case and upper case of the string. fn:containsIgnoreCase work in the same
way as fn:contains but it is not case sensitive which means that it will not
care whether it is in lower case or in upper case. fn:startsWith and
fn:endsWith will also return boolean to check whether the �sentence� starts or
ends with corresponding given value.
Again, clean build
the project and run the project. The index.jsp will appear as usual and click
the �Jstl_Functions_Tags� to see the result.
6.
Conclusion
Now we have known what JSTL is and how to
use it. Use JSTL anytime when possible. JSTL could empower our web app. From
what we learnt, we could think of when or in what conditions JSTL could be used
for. Some examples of use of JSTL are
- display format and internationalization
- print out values from servlets response-request or even
database values as in work with POJO or java bean
- validating users� input on UI
- parsing users� input value
- URL handling
You could think of other
several examples and extend your knowledge on JSTL. And apply it on your
project.
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