Java Notes

JSP Tags and JSTL

Complete guide to JSP tags including standard actions, JSTL core tags, formatting tags, SQL tags, custom tags, and tag files for building maintainable JSP applications.

Why Use Tags Instead of Scriptlets?

Scriptlets (<% %>) mix Java code with HTML, making pages hard to maintain. JSP tags provide a cleaner, XML-like syntax for common operations.

jsp example

<%-- ❌ BAD: Scriptlet approach --%>
<%
    List<String> items = (List<String>) request.getAttribute("items");
    for (String item : items) {
%>
    <li><%= item %></li>
<% } %>

<%-- ✅ GOOD: JSTL approach --%>
<c:forEach var="item" items="${items}">
    <li>${item}</li>
</c:forEach>

JSTL Core Tags (`c:`)

c:out — Output with Escaping

jsp example

<%-- Safely outputs value (escapes HTML to prevent XSS) --%>
<c:out value="${user.name}" />
<c:out value="${user.bio}" default="No bio provided" />
<c:out value="${param.search}" escapeXml="true" />

c:set — Set Variables

jsp example

<%-- Set page-scoped variable --%>
<c:set var="siteName" value="WohoTech" />
<c:set var="year" value="2024" scope="session" />
<c:set var="total" value="${price * quantity}" />

<%-- Set bean property --%>
<c:set target="${user}" property="name" value="John" />

c:remove — Remove Variables

jsp example

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

c:if — Conditional

jsp example

<c:if test="${not empty user}">
    <p>Welcome, ${user.name}!</p>
</c:if>

<c:if test="${user.role == 'admin'}">
    <a href="/admin">Admin Panel</a>
</c:if>

<c:if test="${sessionScope.cart.size() > 0}">
    <p>You have ${sessionScope.cart.size()} items in cart</p>
</c:if>

c:choose / c:when / c:otherwise — Switch-like

jsp example

<c:choose>
    <c:when test="${user.role == 'admin'}">
        <p>Admin Dashboard</p>
    </c:when>
    <c:when test="${user.role == 'teacher'}">
        <p>Teacher Dashboard</p>
    </c:when>
    <c:when test="${user.role == 'student'}">
        <p>Student Dashboard</p>
    </c:when>
    <c:otherwise>
        <p>Guest View</p>
    </c:otherwise>
</c:choose>

c:forEach — Loops

jsp example

<%-- Iterate over collection --%>
<table border="1">
    <tr><th>#</th><th>Name</th><th>Email</th><th>Status</th></tr>
    <c:forEach var="student" items="${students}" varStatus="status">
        <tr class="${status.index % 2 == 0 ? 'even' : 'odd'}">
            <td>${status.count}</td>
            <td>${student.name}</td>
            <td>${student.email}</td>
            <td>
                <c:choose>
                    <c:when test="${student.active}">
                        <span style="color:green">Active</span>
                    </c:when>
                    <c:otherwise>
                        <span style="color:red">Inactive</span>
                    </c:otherwise>
                </c:choose>
            </td>
        </tr>
    </c:forEach>
</table>

<%-- Loop with counter --%>
<c:forEach var="i" begin="1" end="10" step="1">
    <p>Number: ${i}</p>
</c:forEach>

<%-- varStatus properties --%>
<%-- status.index (0-based), status.count (1-based) --%>
<%-- status.first, status.last, status.current --%>

c:forTokens — Split and Iterate

jsp example

<c:forTokens var="color" items="red,green,blue,yellow" delims=",">
    <span style="color:${color}">${color}</span>
</c:forTokens>

c:url and c:param — URL Building

jsp example

<c:url var="searchUrl" value="/search">
    <c:param name="q" value="${query}" />
    <c:param name="page" value="1" />
</c:url>
<a href="${searchUrl}">Search</a>
<%-- Output: /search?q=java&page=1 --%>

c:redirect — Server Redirect

jsp example

<c:if test="${empty sessionScope.user}">
    <c:redirect url="/login.jsp">
        <c:param name="message" value="Please login" />
    </c:redirect>
</c:if>

c:import — Include External Content

jsp example

<c:import url="/header.jsp">
    <c:param name="title" value="Home Page" />
</c:import>

<%-- Include external URL --%>
<c:import url="https://api.example.com/data" var="apiData" />
<p>API Response: ${apiData}</p>

c:catch — Exception Handling

jsp example

<c:catch var="error">
    <% int result = 10 / 0; %>
</c:catch>

<c:if test="${not empty error}">
    <p style="color:red">Error: ${error.message}</p>
</c:if>

JSTL Formatting Tags (`fmt:`)

jsp example

<%@ taglib uri="jakarta.tags.fmt" prefix="fmt" %>

<%-- Format date --%>
<fmt:formatDate value="${now}" pattern="dd-MM-yyyy" />
<fmt:formatDate value="${now}" pattern="hh:mm:ss a" />
<fmt:formatDate value="${now}" type="both" dateStyle="long" timeStyle="short" />

<%-- Format number --%>
<fmt:formatNumber value="${price}" type="currency" currencyCode="INR" />
<fmt:formatNumber value="${percentage}" type="percent" />
<fmt:formatNumber value="${bigNumber}" pattern="#,##,###.##" />

<%-- Parse date --%>
<fmt:parseDate var="parsedDate" value="2024-03-15" pattern="yyyy-MM-dd" />

<%-- Set locale --%>
<fmt:setLocale value="en_IN" />

<%-- Internationalization --%>
<fmt:setBundle basename="messages" />
<fmt:message key="welcome.message" />

JSTL Function Tags (`fn:`)

jsp example

<%@ taglib uri="jakarta.tags.functions" prefix="fn" %>

<p>Length: ${fn:length(name)}</p>
<p>Upper: ${fn:toUpperCase(name)}</p>
<p>Lower: ${fn:toLowerCase(name)}</p>
<p>Contains: ${fn:contains(email, "@gmail.com")}</p>
<p>Starts with: ${fn:startsWith(url, "https")}</p>
<p>Ends with: ${fn:endsWith(file, ".pdf")}</p>
<p>Substring: ${fn:substring(name, 0, 5)}</p>
<p>Replace: ${fn:replace(text, " ", "-")}</p>
<p>Split: ${fn:split(csv, ",")}</p>
<p>Join: ${fn:join(array, ", ")}</p>
<p>Trim: ${fn:trim(input)}</p>
<p>Index: ${fn:indexOf(text, "world")}</p>
<p>Escaped: ${fn:escapeXml(htmlContent)}</p>

JSP Standard Action Tags

jsp example

<%-- Include page at request time --%>
<jsp:include page="sidebar.jsp" flush="true">
    <jsp:param name="section" value="news" />
</jsp:include>

<%-- Forward request --%>
<jsp:forward page="error.jsp">
    <jsp:param name="code" value="404" />
</jsp:forward>

<%-- JavaBean usage --%>
<jsp:useBean id="student" class="com.example.Student" scope="request" />
<jsp:setProperty name="student" property="name" param="name" />
<jsp:setProperty name="student" property="*" />  <%-- auto-set all matching params --%>

Name: <jsp:getProperty name="student" property="name" />
Email: <jsp:getProperty name="student" property="email" />

Custom Tag Library

Tag Handler Class

java example

package com.example.tags;

import jakarta.servlet.jsp.*;
import jakarta.servlet.jsp.tagext.*;
import java.io.*;

public class GreetingTag extends SimpleTagSupport {
    
    private String name;
    private String style;

    public void setName(String name) { this.name = name; }
    public void setStyle(String style) { this.style = style; }

    @Override
    public void doTag() throws JspException, IOException {
        JspWriter out = getJspContext().getOut();
        
        String greeting;
        int hour = java.time.LocalTime.now().getHour();
        if (hour < 12) greeting = "Good Morning";
        else if (hour < 17) greeting = "Good Afternoon";
        else greeting = "Good Evening";
        
        out.println("<div class=\"" + (style != null ? style : "greeting") + "\">");
        out.println("<h3>" + greeting + ", " + name + "!</h3>");
        out.println("</div>");
    }
}

Tag Library Descriptor (TLD)

xml example

<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="https://jakarta.ee/xml/ns/jakartaee" version="3.0">
    <tlib-version>1.0</tlib-version>
    <short-name>myTags</short-name>
    <uri>http://example.com/mytags</uri>
    
    <tag>
        <name>greeting</name>
        <tag-class>com.example.tags.GreetingTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>name</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>style</name>
            <required>false</required>
        </attribute>
    </tag>
</taglib>

Using Custom Tag

jsp example

<%@ taglib uri="http://example.com/mytags" prefix="my" %>

<my:greeting name="${user.name}" style="welcome-box" />

Tag Summary Table

Tag Category	Prefix	Purpose
Core	c:	Variables, conditions, loops, URLs
Formatting	fmt:	Dates, numbers, i18n
Functions	fn:	String manipulation
SQL	sql:	Database queries (avoid in production)
XML	x:	XML processing
Custom	your:	Your own tag libraries

Interview Key Points

JSTL replaces scriptlets for cleaner JSP pages
<c:forEach> is the most commonly used JSTL tag
<c:out> escapes HTML by default (XSS prevention)
${expr} is Expression Language (EL), not JSTL
JSTL requires a JAR file in WEB-INF/lib
Custom tags extend SimpleTagSupport or TagSupport
TLD file defines tag attributes and classes

Summary

In this chapter, we learned about JSP Tags and JSTL in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for JSP Tags and JSTL.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, tags

Continue learning this concept

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PreviousJSP Introduction NextMVC Architecture

Java Notes

JSP Tags and JSTL

Complete guide to JSP tags including standard actions, JSTL core tags, formatting tags, SQL tags, custom tags, and tag files for building maintainable JSP applications.

Why Use Tags Instead of Scriptlets?

Scriptlets (<% %>) mix Java code with HTML, making pages hard to maintain. JSP tags provide a cleaner, XML-like syntax for common operations.

jsp example

<%-- ❌ BAD: Scriptlet approach --%>
<%
    List<String> items = (List<String>) request.getAttribute("items");
    for (String item : items) {
%>
    <li><%= item %></li>
<% } %>

<%-- ✅ GOOD: JSTL approach --%>
<c:forEach var="item" items="${items}">
    <li>${item}</li>
</c:forEach>

JSTL Core Tags (`c:`)

c:out — Output with Escaping

jsp example

<%-- Safely outputs value (escapes HTML to prevent XSS) --%>
<c:out value="${user.name}" />
<c:out value="${user.bio}" default="No bio provided" />
<c:out value="${param.search}" escapeXml="true" />

c:set — Set Variables

jsp example

<%-- Set page-scoped variable --%>
<c:set var="siteName" value="WohoTech" />
<c:set var="year" value="2024" scope="session" />
<c:set var="total" value="${price * quantity}" />

<%-- Set bean property --%>
<c:set target="${user}" property="name" value="John" />

c:remove — Remove Variables

jsp example

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

c:if — Conditional

jsp example

<c:if test="${not empty user}">
    <p>Welcome, ${user.name}!</p>
</c:if>

<c:if test="${user.role == 'admin'}">
    <a href="/admin">Admin Panel</a>
</c:if>

<c:if test="${sessionScope.cart.size() > 0}">
    <p>You have ${sessionScope.cart.size()} items in cart</p>
</c:if>

c:choose / c:when / c:otherwise — Switch-like

jsp example

<c:choose>
    <c:when test="${user.role == 'admin'}">
        <p>Admin Dashboard</p>
    </c:when>
    <c:when test="${user.role == 'teacher'}">
        <p>Teacher Dashboard</p>
    </c:when>
    <c:when test="${user.role == 'student'}">
        <p>Student Dashboard</p>
    </c:when>
    <c:otherwise>
        <p>Guest View</p>
    </c:otherwise>
</c:choose>

c:forEach — Loops

jsp example

<%-- Iterate over collection --%>
<table border="1">
    <tr><th>#</th><th>Name</th><th>Email</th><th>Status</th></tr>
    <c:forEach var="student" items="${students}" varStatus="status">
        <tr class="${status.index % 2 == 0 ? 'even' : 'odd'}">
            <td>${status.count}</td>
            <td>${student.name}</td>
            <td>${student.email}</td>
            <td>
                <c:choose>
                    <c:when test="${student.active}">
                        <span style="color:green">Active</span>
                    </c:when>
                    <c:otherwise>
                        <span style="color:red">Inactive</span>
                    </c:otherwise>
                </c:choose>
            </td>
        </tr>
    </c:forEach>
</table>

<%-- Loop with counter --%>
<c:forEach var="i" begin="1" end="10" step="1">
    <p>Number: ${i}</p>
</c:forEach>

<%-- varStatus properties --%>
<%-- status.index (0-based), status.count (1-based) --%>
<%-- status.first, status.last, status.current --%>

c:forTokens — Split and Iterate

jsp example

<c:forTokens var="color" items="red,green,blue,yellow" delims=",">
    <span style="color:${color}">${color}</span>
</c:forTokens>

c:url and c:param — URL Building

jsp example

<c:url var="searchUrl" value="/search">
    <c:param name="q" value="${query}" />
    <c:param name="page" value="1" />
</c:url>
<a href="${searchUrl}">Search</a>
<%-- Output: /search?q=java&page=1 --%>

c:redirect — Server Redirect

jsp example

<c:if test="${empty sessionScope.user}">
    <c:redirect url="/login.jsp">
        <c:param name="message" value="Please login" />
    </c:redirect>
</c:if>

c:import — Include External Content

jsp example

<c:import url="/header.jsp">
    <c:param name="title" value="Home Page" />
</c:import>

<%-- Include external URL --%>
<c:import url="https://api.example.com/data" var="apiData" />
<p>API Response: ${apiData}</p>

c:catch — Exception Handling

jsp example

<c:catch var="error">
    <% int result = 10 / 0; %>
</c:catch>

<c:if test="${not empty error}">
    <p style="color:red">Error: ${error.message}</p>
</c:if>

JSTL Formatting Tags (`fmt:`)

jsp example

<%@ taglib uri="jakarta.tags.fmt" prefix="fmt" %>

<%-- Format date --%>
<fmt:formatDate value="${now}" pattern="dd-MM-yyyy" />
<fmt:formatDate value="${now}" pattern="hh:mm:ss a" />
<fmt:formatDate value="${now}" type="both" dateStyle="long" timeStyle="short" />

<%-- Format number --%>
<fmt:formatNumber value="${price}" type="currency" currencyCode="INR" />
<fmt:formatNumber value="${percentage}" type="percent" />
<fmt:formatNumber value="${bigNumber}" pattern="#,##,###.##" />

<%-- Parse date --%>
<fmt:parseDate var="parsedDate" value="2024-03-15" pattern="yyyy-MM-dd" />

<%-- Set locale --%>
<fmt:setLocale value="en_IN" />

<%-- Internationalization --%>
<fmt:setBundle basename="messages" />
<fmt:message key="welcome.message" />

JSTL Function Tags (`fn:`)

jsp example

<%@ taglib uri="jakarta.tags.functions" prefix="fn" %>

<p>Length: ${fn:length(name)}</p>
<p>Upper: ${fn:toUpperCase(name)}</p>
<p>Lower: ${fn:toLowerCase(name)}</p>
<p>Contains: ${fn:contains(email, "@gmail.com")}</p>
<p>Starts with: ${fn:startsWith(url, "https")}</p>
<p>Ends with: ${fn:endsWith(file, ".pdf")}</p>
<p>Substring: ${fn:substring(name, 0, 5)}</p>
<p>Replace: ${fn:replace(text, " ", "-")}</p>
<p>Split: ${fn:split(csv, ",")}</p>
<p>Join: ${fn:join(array, ", ")}</p>
<p>Trim: ${fn:trim(input)}</p>
<p>Index: ${fn:indexOf(text, "world")}</p>
<p>Escaped: ${fn:escapeXml(htmlContent)}</p>

JSP Standard Action Tags

jsp example

<%-- Include page at request time --%>
<jsp:include page="sidebar.jsp" flush="true">
    <jsp:param name="section" value="news" />
</jsp:include>

<%-- Forward request --%>
<jsp:forward page="error.jsp">
    <jsp:param name="code" value="404" />
</jsp:forward>

<%-- JavaBean usage --%>
<jsp:useBean id="student" class="com.example.Student" scope="request" />
<jsp:setProperty name="student" property="name" param="name" />
<jsp:setProperty name="student" property="*" />  <%-- auto-set all matching params --%>

Name: <jsp:getProperty name="student" property="name" />
Email: <jsp:getProperty name="student" property="email" />

Custom Tag Library

Tag Handler Class

java example

package com.example.tags;

import jakarta.servlet.jsp.*;
import jakarta.servlet.jsp.tagext.*;
import java.io.*;

public class GreetingTag extends SimpleTagSupport {
    
    private String name;
    private String style;

    public void setName(String name) { this.name = name; }
    public void setStyle(String style) { this.style = style; }

    @Override
    public void doTag() throws JspException, IOException {
        JspWriter out = getJspContext().getOut();
        
        String greeting;
        int hour = java.time.LocalTime.now().getHour();
        if (hour < 12) greeting = "Good Morning";
        else if (hour < 17) greeting = "Good Afternoon";
        else greeting = "Good Evening";
        
        out.println("<div class=\"" + (style != null ? style : "greeting") + "\">");
        out.println("<h3>" + greeting + ", " + name + "!</h3>");
        out.println("</div>");
    }
}

Tag Library Descriptor (TLD)

xml example

<?xml version="1.0" encoding="UTF-8"?>
<taglib xmlns="https://jakarta.ee/xml/ns/jakartaee" version="3.0">
    <tlib-version>1.0</tlib-version>
    <short-name>myTags</short-name>
    <uri>http://example.com/mytags</uri>
    
    <tag>
        <name>greeting</name>
        <tag-class>com.example.tags.GreetingTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>name</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>style</name>
            <required>false</required>
        </attribute>
    </tag>
</taglib>

Using Custom Tag

jsp example

<%@ taglib uri="http://example.com/mytags" prefix="my" %>

<my:greeting name="${user.name}" style="welcome-box" />

Tag Summary Table

Tag Category	Prefix	Purpose
Core	c:	Variables, conditions, loops, URLs
Formatting	fmt:	Dates, numbers, i18n
Functions	fn:	String manipulation
SQL	sql:	Database queries (avoid in production)
XML	x:	XML processing
Custom	your:	Your own tag libraries

Interview Key Points

JSTL replaces scriptlets for cleaner JSP pages
<c:forEach> is the most commonly used JSTL tag
<c:out> escapes HTML by default (XSS prevention)
${expr} is Expression Language (EL), not JSTL
JSTL requires a JAR file in WEB-INF/lib
Custom tags extend SimpleTagSupport or TagSupport
TLD file defines tag attributes and classes

Summary

In this chapter, we learned about JSP Tags and JSTL in detail. Here are the key points:

Basic introduction to the concept and why it is needed
Syntax and structure with complete examples
Internal working and best practices
Real-world applications and use cases
Common mistakes and how to avoid them
How this topic is asked in interviews

To practice these concepts, write and run the code in your IDE and verify the output. Modify each example and experiment so that you deeply understand the concept.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for JSP Tags and JSTL.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Java Master Course topic.

Search Terms

java-master-course, java master course, java, master, course, servlets, jsp, tags

Continue learning this concept

PreviousJSP Introduction NextMVC Architecture

Why Use Tags Instead of Scriptlets?

JSTL Core Tags (c:)

c:out — Output with Escaping

c:set — Set Variables

c:remove — Remove Variables

c:if — Conditional

c:choose / c:when / c:otherwise — Switch-like

c:forEach — Loops

c:forTokens — Split and Iterate

c:url and c:param — URL Building

c:redirect — Server Redirect

c:import — Include External Content

c:catch — Exception Handling

JSTL Formatting Tags (fmt:)

JSTL Function Tags (fn:)

JSP Standard Action Tags

Custom Tag Library

Tag Handler Class

Tag Library Descriptor (TLD)

Using Custom Tag

Tag Summary Table

Interview Key Points

Summary

Continue learning this concept

Why Use Tags Instead of Scriptlets?

JSTL Core Tags (c:)

c:out — Output with Escaping

c:set — Set Variables

c:remove — Remove Variables

c:if — Conditional

c:choose / c:when / c:otherwise — Switch-like

c:forEach — Loops

c:forTokens — Split and Iterate

c:url and c:param — URL Building

c:redirect — Server Redirect

c:import — Include External Content

c:catch — Exception Handling

JSTL Formatting Tags (fmt:)

JSTL Function Tags (fn:)

JSP Standard Action Tags

Custom Tag Library

Tag Handler Class

Tag Library Descriptor (TLD)

Using Custom Tag

Tag Summary Table

Interview Key Points

Summary

Continue learning this concept

JSTL Core Tags (`c:`)

JSTL Formatting Tags (`fmt:`)

JSTL Function Tags (`fn:`)

JSTL Core Tags (`c:`)

JSTL Formatting Tags (`fmt:`)

JSTL Function Tags (`fn:`)