Java Server Pages

JSP

page directive

// Set encoding of the response
<%@ page contentType="text/html; charset=UTF-8" %>

<%@ page errorPage="errorpage.jsp" %>

<%@ page isErrorPage="true" %>

// To set the source encoding of the page itself
<%@ page pageEncoding="UTF-8" %>

Import classes in JSP

<%@ page import="java.util.List" %>

<%-- If you want to import multiple classes --%>
<%@ page import="package1.myClass1,package2.myClass2,....,packageN.myClassN" %>

JSTL

if

<c:if test="${empty someFlag}">
 ...
</c:if>

<!-- not case -->
<!-- can also be done !empty -->
<c:if test="${not empty someFlag}">
 ...
</c:if>

For testing null and boolean property

<c:if test="${isDataSet != null && isDataSet}">
   <!-- Do something if isDataSet is available and set to true -->
</c:if>

if else / choose

<c:choose>
  <c:when test="${condition1}">
    ...
  </c:when>
  <c:when test="${condition2}">
    ...
  </c:when>
  <c:otherwise>
    ...
  </c:otherwise>
</c:choose>

Conditional operator (?)

<c:out value="" />

Get index in forEach 002

<c:forEach items="${itemsList}" var="item"  varStatus="loop">
   <p>Item: ${item} had Index: ${loop.index}</p>
</c:forEach>

Iterate Map 001

For accessing Map<Key, Value>

<c:forEach items="${list}" var="map">
   <c:forEach items="${map}" var="entry">
     Key: ${entry.key}<br>
     Value: ${entry.value}<br>
   </c:forEach>
</c:forEach>

empty operator 003

1.10 Empty Operator - empty A

The empty operator is a prefix operator that can be used to determine if a value is null or empty.

To evaluate empty A

  • If A is null, return true

  • Otherwise, if A is the empty string, then return true

  • Otherwise, if A is an empty array, then return true

  • Otherwise, if A is an empty Map`, return ``true

  • Otherwise, if A is an empty Collection, return true

  • Otherwise return false

EL not being evaluated

If Expression Languages is not being evaluated and getting the same expression. Need to set isELIgnored="false"

This can be set at page level or in web.xml for entire web application.

Templating using Tag files

Tag declaration

<%@ taglib tagdir="/WEB-INF/tags/my" prefix="my" %>

Here my can be whatever you want

Tag structure

<prefix:name [attribute=value] ... />

<% -- OR --%>

<prefix:name [attribute=value] ... />

// Any body element nested within the tag

</prefix:name>

Here prefix is user assigned namespace

  • Tag files need to have suffix/extension .tag

  • Can only be placed in /WEB-INF/tags/

  • TLD is not mandatory for tag files. But, are recommended

  • if the tag file name is userdetail.tag then the tag name is userdetail

  • request, session, application had same scope as the page invocking the tag

  • A fresh, clean page scope is setup for each invocation of the tag, and does not affect the invoking JSP page

example:

<%@ taglib prefix="my" tagdir="/WEB-INF/tags/m" %>

<my:sample />

Here <my:sample /> refers to /WEB-INF/tags/m/sample.tag