Java Notes

Expression Language (EL)

Complete guide to JSP Expression Language (EL) - syntax, operators, implicit objects, accessing beans, collections, and EL functions for clean JSP development.

What is Expression Language?

Expression Language (EL) is a simple scripting language used in JSP to access data stored in JavaBeans, request/session attributes, and other sources without writing Java code. EL uses the syntax ${expression}.

EL Syntax

Basic Syntax

jsp example

${expression}    <%-- Immediate evaluation --%>
#{expression}    <%-- Deferred evaluation (used in JSF) --%>

Accessing Properties

Example

<%-- Dot notation --%> ${user.name} <%-- calls user.getName() --%> ${user.address.city} <%-- calls user.getAddress().getCity() --%> <%-- Bracket notation --%> ${user["name"]} <%-- same as user.getName() --%> ${user[propName]} <%-- dynamic property access --%> <%-- Array/List access --%> ${colors[0]} <%-- first element --%> ${students[2].name} <%-- third student's name --%> <%-- Map access --%> ${settings["theme"]} <%-- map.get("theme") --%> ${settings.theme} <%-- same thing --%>

EL Operators

Arithmetic Operators

jsp example

${10 + 5}       <%-- 15 --%>
${10 - 5}       <%-- 5 --%>
${10 * 5}       <%-- 50 --%>
${10 / 5}       <%-- 2 (or use: ${10 div 5}) --%>
${10 % 3}       <%-- 1 (or use: ${10 mod 3}) --%>

Comparison Operators

jsp example

${age == 18}     <%-- or: ${age eq 18} --%>
${age != 18}     <%-- or: ${age ne 18} --%>
${age > 18}      <%-- or: ${age gt 18} --%>
${age < 18}      <%-- or: ${age lt 18} --%>
${age >= 18}     <%-- or: ${age ge 18} --%>
${age <= 18}     <%-- or: ${age le 18} --%>

Logical Operators

Example

${age > 18 && age < 65} <%-- or: ${age gt 18 and age lt 65} --%> ${isAdmin || isModerator} <%-- or: ${isAdmin or isModerator} --%> ${!isBlocked} <%-- or: ${not isBlocked} --%>

Empty Operator

jsp example

${empty name}           <%-- true if name is null, "", empty collection/array --%>
${not empty users}      <%-- true if users has elements --%>
${empty param.search}   <%-- true if no search parameter --%>

Ternary Operator (EL 3.0+)

jsp example

${user.active ? "Active" : "Inactive"}
${empty cart ? "Empty Cart" : cart.size().toString().concat(" items")}

EL Implicit Objects

Object	Type	Description
`pageScope`	Map	Page-scoped attributes
`requestScope`	Map	Request-scoped attributes
`sessionScope`	Map	Session-scoped attributes
`applicationScope`	Map	Application-scoped attributes
`param`	Map	Request parameters (single value)
`paramValues`	Map	Request parameters (array)
`header`	Map	HTTP headers (single value)
`headerValues`	Map	HTTP headers (array)
`cookie`	Map	Cookies
`initParam`	Map	Context init parameters
`pageContext`	PageContext	Access to request, session, etc.

Using Implicit Objects

Example

<%-- Request parameters --%> Search: ${param.q} Page: ${param.page} Hobbies: ${paramValues.hobby[0]}, ${paramValues.hobby[1]} <%-- Scoped attributes --%> ${requestScope.errorMessage} ${sessionScope.loggedInUser} ${applicationScope.totalUsers} <%-- Headers --%> User-Agent: ${header["User-Agent"]} Accept: ${header.Accept} <%-- Cookies --%> Theme: ${cookie.theme.value} Session: ${cookie.JSESSIONID.value} <%-- Context parameters (from web.xml) --%> App Name: ${initParam.appName} Version: ${initParam.version} <%-- PageContext --%> Context Path: ${pageContext.request.contextPath} HTTP Method: ${pageContext.request.method} Server Name: ${pageContext.request.serverName} Session ID: ${pageContext.session.id}

EL Scope Resolution

When you write ${user}, EL searches in this order:

pageScope — Page attributes
requestScope — Request attributes
sessionScope — Session attributes
applicationScope — Application attributes

To be explicit:

jsp example

${requestScope.user}     <%-- only look in request --%>
${sessionScope.user}     <%-- only look in session --%>

Accessing JavaBeans with EL

JavaBean Class

java example

package com.example;

public class Student {
    private String name;
    private String email;
    private int age;
    private Address address;
    private List<String> courses;

    // Getters and setters
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public Address getAddress() { return address; }
    public void setAddress(Address address) { this.address = address; }
    public List<String> getCourses() { return courses; }
    public void setCourses(List<String> courses) { this.courses = courses; }
}

Servlet Sets the Bean

java example

Student student = new Student();
student.setName("Rahul");
student.setEmail("rahul@example.com");
student.setAge(22);
student.setCourses(Arrays.asList("Java", "Spring", "React"));

request.setAttribute("student", student);
request.getRequestDispatcher("/profile.jsp").forward(request, response);

JSP Accesses with EL

Example

<h2>Student Profile</h2> Name: ${student.name} Email: ${student.email} Age: ${student.age} City: ${student.address.city} First Course: ${student.courses[0]} Total Courses: ${student.courses.size()} <%-- Conditional display --%> Status: ${student.age >= 18 ? "Adult" : "Minor"} Has courses: ${not empty student.courses}

EL with Collections

Example

<%-- List access --%> First item: ${myList[0]} Last item: ${myList[myList.size() - 1]} Size: ${myList.size()} <%-- Map access --%> Value: ${myMap["key1"]} Value: ${myMap.key1} <%-- Combined with JSTL --%> <c:forEach var="entry" items="${myMap}"> ${entry.key} = ${entry.value} </c:forEach>

EL 3.0+ Features (Java EE 7+)

Lambda Expressions

Example

${[1,2,3,4,5].stream().filter(x -> x > 3).toList()} ${students.stream().map(s -> s.name).toList()} ${numbers.stream().sum()} ${items.stream().filter(i -> i.price > 100).count()}

Collection Operations

Example

${[3,1,4,1,5].stream().sorted().toList()} ${["banana","apple","cherry"].stream().sorted().toList()}

String Operations

jsp example

${"Hello World".toUpperCase()}
${"Hello World".substring(0, 5)}
${"Hello World".replace("World", "Java")}

Disabling EL

jsp example

<%-- Disable EL for entire page --%>
<%@ page isELIgnored="true" %>

<%-- Or in web.xml for all pages --%>
<jsp-config>
    <jsp-property-group>
        <url-pattern>*.jsp</url-pattern>
        <el-ignored>true</el-ignored>
    </jsp-property-group>
</jsp-config>

Complete Example: Product Listing Page

Servlet (Controller)

java example

@WebServlet("/products")
public class ProductServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        List<Product> products = productService.getAllProducts();
        request.setAttribute("products", products);
        request.setAttribute("totalCount", products.size());
        request.setAttribute("category", request.getParameter("cat"));
        
        request.getRequestDispatcher("/products.jsp").forward(request, response);
    }
}

JSP (View) with EL

jsp example

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

<h2>Products (${totalCount} found)</h2>

<c:if test="${not empty category}">
    <p>Filtered by: ${fn:toUpperCase(category)}</p>
</c:if>

<c:choose>
    <c:when test="${empty products}">
        <p>No products found.</p>
    </c:when>
    <c:otherwise>
        <table>
            <c:forEach var="product" items="${products}" varStatus="s">
                <tr class="${s.index % 2 == 0 ? 'row-even' : 'row-odd'}">
                    <td>${s.count}</td>
                    <td>${product.name}</td>
                    <td><fmt:formatNumber value="${product.price}" type="currency" /></td>
                    <td>${product.inStock ? 'Available' : 'Out of Stock'}</td>
                </tr>
            </c:forEach>
        </table>
    </c:otherwise>
</c:choose>

Interview Key Points

EL uses ${expr} syntax to access data without Java code
EL is null-safe — returns "" instead of NullPointerException
Scope search order: page → request → session → application
${bean.property} calls the getter method automatically
empty operator checks null, "", empty collections/arrays
EL 3.0 supports lambdas and stream operations
Use bracket notation for dynamic property names: ${bean[varName]}

Summary

In this chapter, we learned about Expression Language (EL) 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 Expression Language (EL).

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, expression

Continue learning this concept

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Java Notes

Expression Language (EL)

Complete guide to JSP Expression Language (EL) - syntax, operators, implicit objects, accessing beans, collections, and EL functions for clean JSP development.

What is Expression Language?

EL Syntax

Basic Syntax

jsp example

${expression}    <%-- Immediate evaluation --%>
#{expression}    <%-- Deferred evaluation (used in JSF) --%>

Accessing Properties

Example

EL Operators

Arithmetic Operators

jsp example

${10 + 5}       <%-- 15 --%>
${10 - 5}       <%-- 5 --%>
${10 * 5}       <%-- 50 --%>
${10 / 5}       <%-- 2 (or use: ${10 div 5}) --%>
${10 % 3}       <%-- 1 (or use: ${10 mod 3}) --%>

Comparison Operators

jsp example

${age == 18}     <%-- or: ${age eq 18} --%>
${age != 18}     <%-- or: ${age ne 18} --%>
${age > 18}      <%-- or: ${age gt 18} --%>
${age < 18}      <%-- or: ${age lt 18} --%>
${age >= 18}     <%-- or: ${age ge 18} --%>
${age <= 18}     <%-- or: ${age le 18} --%>

Logical Operators

Example

${age > 18 && age < 65} <%-- or: ${age gt 18 and age lt 65} --%> ${isAdmin || isModerator} <%-- or: ${isAdmin or isModerator} --%> ${!isBlocked} <%-- or: ${not isBlocked} --%>

Empty Operator

jsp example

${empty name}           <%-- true if name is null, "", empty collection/array --%>
${not empty users}      <%-- true if users has elements --%>
${empty param.search}   <%-- true if no search parameter --%>

Ternary Operator (EL 3.0+)

jsp example

${user.active ? "Active" : "Inactive"}
${empty cart ? "Empty Cart" : cart.size().toString().concat(" items")}

EL Implicit Objects

Object	Type	Description
`pageScope`	Map	Page-scoped attributes
`requestScope`	Map	Request-scoped attributes
`sessionScope`	Map	Session-scoped attributes
`applicationScope`	Map	Application-scoped attributes
`param`	Map	Request parameters (single value)
`paramValues`	Map	Request parameters (array)
`header`	Map	HTTP headers (single value)
`headerValues`	Map	HTTP headers (array)
`cookie`	Map	Cookies
`initParam`	Map	Context init parameters
`pageContext`	PageContext	Access to request, session, etc.

Using Implicit Objects

Example

EL Scope Resolution

When you write ${user}, EL searches in this order:

pageScope — Page attributes
requestScope — Request attributes
sessionScope — Session attributes
applicationScope — Application attributes

To be explicit:

jsp example

${requestScope.user}     <%-- only look in request --%>
${sessionScope.user}     <%-- only look in session --%>

Accessing JavaBeans with EL

JavaBean Class

java example

package com.example;

public class Student {
    private String name;
    private String email;
    private int age;
    private Address address;
    private List<String> courses;

    // Getters and setters
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    public Address getAddress() { return address; }
    public void setAddress(Address address) { this.address = address; }
    public List<String> getCourses() { return courses; }
    public void setCourses(List<String> courses) { this.courses = courses; }
}

Servlet Sets the Bean

java example

Student student = new Student();
student.setName("Rahul");
student.setEmail("rahul@example.com");
student.setAge(22);
student.setCourses(Arrays.asList("Java", "Spring", "React"));

request.setAttribute("student", student);
request.getRequestDispatcher("/profile.jsp").forward(request, response);

JSP Accesses with EL

Example

EL with Collections

Example

EL 3.0+ Features (Java EE 7+)

Lambda Expressions

Example

${[1,2,3,4,5].stream().filter(x -> x > 3).toList()} ${students.stream().map(s -> s.name).toList()} ${numbers.stream().sum()} ${items.stream().filter(i -> i.price > 100).count()}

Collection Operations

Example

${[3,1,4,1,5].stream().sorted().toList()} ${["banana","apple","cherry"].stream().sorted().toList()}

String Operations

jsp example

${"Hello World".toUpperCase()}
${"Hello World".substring(0, 5)}
${"Hello World".replace("World", "Java")}

Disabling EL

jsp example

<%-- Disable EL for entire page --%>
<%@ page isELIgnored="true" %>

<%-- Or in web.xml for all pages --%>
<jsp-config>
    <jsp-property-group>
        <url-pattern>*.jsp</url-pattern>
        <el-ignored>true</el-ignored>
    </jsp-property-group>
</jsp-config>

Complete Example: Product Listing Page

Servlet (Controller)

java example

@WebServlet("/products")
public class ProductServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        
        List<Product> products = productService.getAllProducts();
        request.setAttribute("products", products);
        request.setAttribute("totalCount", products.size());
        request.setAttribute("category", request.getParameter("cat"));
        
        request.getRequestDispatcher("/products.jsp").forward(request, response);
    }
}

JSP (View) with EL

jsp example

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

<h2>Products (${totalCount} found)</h2>

<c:if test="${not empty category}">
    <p>Filtered by: ${fn:toUpperCase(category)}</p>
</c:if>

<c:choose>
    <c:when test="${empty products}">
        <p>No products found.</p>
    </c:when>
    <c:otherwise>
        <table>
            <c:forEach var="product" items="${products}" varStatus="s">
                <tr class="${s.index % 2 == 0 ? 'row-even' : 'row-odd'}">
                    <td>${s.count}</td>
                    <td>${product.name}</td>
                    <td><fmt:formatNumber value="${product.price}" type="currency" /></td>
                    <td>${product.inStock ? 'Available' : 'Out of Stock'}</td>
                </tr>
            </c:forEach>
        </table>
    </c:otherwise>
</c:choose>

Interview Key Points

EL uses ${expr} syntax to access data without Java code
EL is null-safe — returns "" instead of NullPointerException
Scope search order: page → request → session → application
${bean.property} calls the getter method automatically
empty operator checks null, "", empty collections/arrays
EL 3.0 supports lambdas and stream operations
Use bracket notation for dynamic property names: ${bean[varName]}

Summary

In this chapter, we learned about Expression Language (EL) 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 Expression Language (EL).

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, expression

Continue learning this concept

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