JSP Declarations

Initializing and Finalizing a JSP Page

JSP Declarations

A JSP declaration is used to declare variables and methods in a page’s scripting language. The syntax for a declaration is as follows:

<%! scripting-language-declaration %>

When the scripting language is the Java programming language, variables and methods in JSP declarations become declarations in the JSP page’s servlet class.

Initializing and Finalizing a JSP Page

You can customize the initialization process to allow the JSP page to read persistent configuration data, initialize resources, and perform any other one-time activities; to do so, you override the jspInit method of the JspPage interface. You release resources using the jspDestroy method. The methods are defined using JSP declarations.

For example, an older version of the Duke’s Bookstore application retrieved the object that accesses the bookstore database from the context and stored a reference to the object in the variable bookDBAO in the jspInit method. The variable definition and the initialization and finalization methods jspInit and jspDestroy were defined in a declaration:

<%!
private BookDBAO bookDBAO;
public void jspInit() { 
bookDBAO =
 (BookDBAO)getServletContext().getAttribute("bookDB");
 if (bookDBAO == null)
 System.out.println("Couldn’t get database.");
}
%>

When the JSP page was removed from service, the jspDestroy method released the BookDBAO variable.

<%!
public void jspDestroy() {
 bookDBAO = null;
}
%>

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