JSP Scopes and Expression Language (EL)

1. JSP Scopes

JSP scopes define the visibility and lifetime of variables in JSP pages. There are four major scopes in JSP:

• pageScope: This scope is used within the current page only. Once the request is processed, the variable goes out of scope.
• requestScope: The variable is available as long as the request is alive. It is visible to all resources that handle the request (e.g., servlets, JSPs, etc.).
• sessionScope: This scope allows variables to persist across multiple requests from the same user during a session. It is visible across multiple pages as long as the session is valid.
• applicationScope: The variable is available across all servlets and JSPs in the application. It lasts for the entire lifecycle of the web application.

2. JSP Expression Language (EL)

JSP Expression Language (EL) provides a simplified syntax for accessing data in JSP pages. It allows you to express dynamic content in a more readable and concise way.

EL expressions are written between ${} and can be used to access values from various scopes (e.g., page, request, session, application), as well as objects in JavaBeans, collections, or other objects stored in the request.

EL Syntax:

  ${expression}

The ${} syntax is used to evaluate an expression and display its result.

3. EL Expressions Examples:

Here are some examples of EL expressions:

• Accessing request scope attribute: ${requestScope.username}
• Accessing session scope attribute: ${sessionScope.user}
• Accessing page scope attribute: ${pageScope.title}
• Accessing application scope attribute: ${applicationScope.appName}
• Accessing a JavaBean property: ${user.name}
• Mathematical operations: ${2 + 3}
• Using conditional statements: ${age > 18 ? 'Adult' : 'Minor'}

Example: Accessing Variables with EL:

<%-- JSP Page -->
<%
  request.setAttribute("username", "John Doe");
  session.setAttribute("user", "Jane Doe");
  pageContext.setAttribute("title", "Welcome Page");
  application.setAttribute("appName", "CIQ demo app");
%>

<h1>Welcome, ${requestScope.username}</h1>
<p>Your session user is: ${sessionScope.user}</p>
<p>Page Title: ${pageScope.title}</p>
<p>App name: ${application.appName}</p>

3. Implicit Objects in EL

JSP provides several implicit objects that can be accessed in EL expressions. These are pre-defined objects that can be used directly within JSP pages.

Summary of JSP Scopes and EL Expressions