What do you know about the JSP expression language, known as JSP Expression Language (EL)?

JSP Expression Language (EL) is a language of expressions used in JSP to access data of Java components (such as JavaBeans) and perform basic operations.

Main features:

• Access to properties: Allows retrieving property values of objects.

  ${user.name}  
  

• Access to collection elements: Allows retrieving elements of arrays and collections by index or key.

  ${users[0]}  
  ${map['key']}  
  

• Arithmetic operations: Supports addition, subtraction, multiplication, and division.

  ${price * quantity}  
  

• Logical operations: Supports comparison (==, !=, <, >, <=, >=), logical AND (and, &&), OR (or, ||), NOT (not, !).

  ${user.age ge 18}  
  

• instanceof operation: Checks the type of an object.

  ${object instanceof 'java.lang.String'}  
  

• Ternary operator: Conditional expression in a single line.

  ${status == 'active' ? 'Active' : 'Inactive'}  
  

• Explicit and implicit objects: Access to objects such as pageContext, request, session, application, param, paramValues, header, headerValues, cookie.

Table of implicit EL objects:

Object	Description
pageContext	JSP PageContext
pageScope	Map of page-level attributes
requestScope	Map of request-level attributes
sessionScope	Map of session-level attributes
applicationScope	Map of application-level attributes
param	Map of request parameters (first value)
paramValues	Map of request parameters (all values)
header	Map of request HTTP headers (first value)
headerValues	Map of request HTTP headers (all values)
cookie	Map of Cookie objects
initParam	Map of servlet initialization parameters

EL simplifies data access in JSP and reduces the use of scriptlets (<% %>), making pages more readable and maintainable. It is used in JSP 2.0 and above.