JSTL Tags Overview

1. <c:set> Tag

The <c:set> tag is used to set a variable or assign a value to an attribute in different scopes.

Syntax:

<c:set var="variableName" value="expression" scope="scope" />

• var: The name of the variable to be set.
• value: The value or expression to assign.
• scope (optional): Can be page, request, session, or application.

Example of <c:set>:

<!-- Setting a string value -->
<c:set var="greeting" value="Hello, World!" />

<!-- Setting the result of an expression -->
<c:set var="sum" value="${5 + 10}" />

<!-- Setting a session-scoped variable -->
<c:set var="user" value="John Doe" scope="session" />

2. <c:when> Tag

The <c:when> tag is used in combination with <c:choose> for conditional logic. It works like an if statement and allows you to check conditions.

Syntax:

<c:choose>
    <c:when test="condition">
        <!-- Code executed when the condition is true -->
    </c:when>
    <c:otherwise>
        <!-- Code executed when no conditions are true -->
    </c:otherwise>
</c:choose>

Example of <c:when>:

<c:choose>
    <c:when test="${age < 18}">
        <p>You are a minor.</p>
    </c:when>
    <c:when test="${age >= 18}">
        <p>You are an adult.</p>
    </c:when>
    <c:otherwise>
        <p>Age is unknown.</p>
    </c:otherwise>
</c:choose>

3. <c:choose> Tag

The <c:choose> tag works like a switch statement, providing multiple conditions to check.

Example of <c:choose>:

<c:choose>
    <c:when test="${user.role == 'admin'}">
        <p>Welcome, admin!</p>
    </c:when>
    <c:when test="${user.role == 'guest'}">
        <p>Welcome, guest!</p>
    </c:when>
    <c:otherwise>
        <p>Access denied.</p>
    </c:otherwise>
</c:choose>

4. <c:forEach> Tag

The <c:forEach> tag is used to iterate over collections or arrays.

Syntax:

<c:forEach var="item" items="collectionOrArray">
    <!-- Code to execute for each item -->
</c:forEach>

Example of <c:forEach>:

<c:forEach var="item" items="${itemList}">
    <p>${item.name}</p>
</c:forEach>

Conclusion

JSTL provides a set of powerful tags for common tasks such as iteration, conditionals, and data manipulation. These tags help simplify JSP development by reducing the need for Java code within JSP files.