JSP | Declaration Tag

The Declaration Tag in JSP is used to declare variables, methods, and classes in a JSP page. The code written inside this tag is placed outside the _jspService() method by the JSP container, making it available throughout the JSP page.

• Uses <%! %> syntax to declare variables, methods, and classes
• Declarations become class-level members of the generated servlet
• Used for defining reusable logic, not for direct output

Syntax:

<%! declaration code %>

Example: JSP Declaration Tag which initializes a string

Output: 

Explanation:

• <%! String username = "Geeks"; %> → Declares a class-level variable named username
• This variable is stored outside _jspService(), so it is accessible throughout the JSP
• <%= "Hello: " + username %> → Uses Expression Tag to display the value on browser

Example : JSP Declaration Tag which initializes a method 

Output

Explanation:

• <%! int factorial(int n) { ... } %> -> Declares a method inside JSP
• The method is part of the generated servlet class and can be reused
• return n * factorial(n - 1) -> Uses recursion to calculate factorial
• <%= factorial(5) %> -> Calls the method and prints result using Expression Tag