JSP Standard Tag Library (JSTL)

The JavaServer Pages Standard Tag Library (JSTL) is a standard set of commonly used tag libraries. That is, JSTL encapsulates core functionality common to many JSP applications. For example, instead of iterating over lists using a scriptlet or different iteration tags from numerous vendors, JSTL defines a standard set of iteration tags. JSTL has tags for common structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization tags, and tags for accessing databases using SQL.

Looking for JSP Custom Tags

Why JSTL?

<c:remove var="cart" scope="session"/>

<c:forEach var="customer" items="${customers}">
  <c:if test="${customer.address.country == 'USA'}">
    ${customer}<br>
  </c:if>
</c:forEach>

<c:forEach var="customer" items="${customers}">
  <c:choose>
    <c:when test="${customer.address.country == 'USA'}">
      <font color="blue">
    </c:when>
    <c:when test="${customer.address.country == 'Canada'}">
      <font color="red">
    </c:when>
    <c:otherwise>
      <font color="green"> 
    </c:otherwise> 
  </c:choose>
  ${customer}</font><br>
</c:forEach>

<c:forEach var="customer" items="${customers}">
  ${customer}<br>
</c:forEach

Example: <c:forToken>

<c:forTokens var="token" items="one,two,three" delims=",">
<c:out value="${token}"/>
</c:forTokens>

URL Management Tags

URL Import: <c:import>

Example:

<blockquote>
<ex:escapeHtml>
  <c:import url="http://www.cnn.com/cnn.rss"/>
</ex:escapeHtml>
</blockquote>

Example: <c:import>  with <c:param>

<c:import url="header.jsp">
     <c:param name="pageTitle" value="newInstance.com"/>
     <c:param name="pageSlogan" value=" " />
</c:import>

URL Rewriting: <c:url>

Example: <c:url>

<table border="1" bgcolor="#dddddd">
 <tr>
  <td>"base", param=ABC</td>
  <td>
<c:url value="base">
         <c:param name="param" value="ABC"/>
      </c:url>
  </td>
 </tr>
 <tr>
  <td>"base", param=123</td>
  <td>
         <c:url value="base">
           <c:param name="param" value="123"/>
         </c:url>
  </td>
 </tr>
 <tr>

Redirection: <c:redirect>

The redirect tag sends an HTTP redirect to the client. The redirect tag takes param subtags for including parameters in the returned URL.

General Purpose Tags

Example: <c:out>

<table border="1">
  <c:forEach var="customer" items="${customers}">
    <tr>
      <td><c:out value="${customer.lastName}"/></td>
      <td><c:out value="${customer.phoneHome}" default="no home phone specified"/></td>
      <td>
        <c:out value="${customer.phoneCell}" escapeXml="false">
          <font color="red">no cell phone specified</font>
        </c:out>
      </td>
    </tr>
  </c:forEach>
</table>

Database Access Tags

In production environment, the database access logic is typically captured within JavaBeans which functions as a Model under MVC architecture.  This state of the JavaBeans is set by the Controller (Servlet) and then is accessed by the JSP pages (View).

DataSource

All DB actions operate on a DataSource. Different ways to access a DataSource:

<sql:dataSource var="dataSource"
      driver="org.gjt.mm.mysql.Driver"
      url="jdbc:..."/>
 <sql:query dataSource="${dataSource}" .../>

For Example:

<sql:setDataSource
  var="example"
  driver="com.pointbase.jdbc.jdbcUniversalDriver"
  url="jdbc:pointbase:server://localhost:1092/jstlsample;create=true"
/>

Example: 

This example shows the creation of a very simple database and then populating the table.  Then querying the database table and save the query result into a scope variable “deejays”.

<sql:transaction dataSource="${example}">
  <sql:update var="newTable">
    create table mytable (
      nameid int primary key,
      name varchar(80)‏
    )‏
  </sql:update>
  <sql:update var="updateCount">
    INSERT INTO mytable VALUES (1,'Paul Oakenfold')‏
  </sql:update>
  <sql:update var="updateCount">
    INSERT INTO mytable VALUES (2,'Timo Maas')‏
  </sql:update>
  ...
  <sql:query var="deejays">
    SELECT * FROM mytable
  </sql:query>

</sql:transaction>

XML Tags

XML tags are used to access information stored in XML document.  Now what is unique about XML tags is that the access description is specified in XPath expression as a value of “select” attribute as shown in the slide above.  Except that the access description is described in XPath expression, the flow control, iteration, and general purpose tags work similarly as corresponding tags in Core tags.

• Flow control
• <x:choose>, <x:when>, <x:if>, <x:otherwise>
• Iteration
• <x:forEach>
• General purpose
• <x:out>
• <x:set>
• Parsing and Transformation
• <x:parse>
• <x:transform> with <x:param> subtags

We’ll discuss only <x:parse> and <x:out> tags here.

<x:parse>

<x:parse> tag is for parsing XML document into a scoped varilable. This requires x-path queries that is beyond the scope of this article. If you don’t understand this, then please leave <x:parse> here and move to the next heading.

Example:

<c:set var="xmlText">
   <a>
        <b>
             <c>
                foo
             </c>
        </b>
        <d>
                bar
        </d>
  </a>
</c:set>   
<x:parse var="a" doc="${xmlText}" />
<x:out select="$a//c"/>
<x:out select="$a/a/d"/>

<x:out>

Example:

        <tr>
          <td>$doc//sport</td>
          <td><pre><x:out select="$doc//sport"/></pre></td>
        </tr>
        <tr>
          <td>$doc/games/country/*</td>
          <td><pre><x:out select="$doc/games/country/*"/></pre></td>
        </tr>
        <tr>
          <td>$doc//*</td>
          <td><pre><x:out select="$doc//*"/></pre></td>
        </tr>
        <tr>
          <td>$doc/games/country</td>
          <td><pre><x:out select="$doc/games/country"/></pre></td>
        </tr>

EL Functions

Following list shows the EL functions that you can use in JSP.

Formatting Tags

JSTL provides a set of tags for parsing and formatting locale-sensitive numbers and dates.

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