jspInit() and jspDestroy( )

If you know a bit about servlets, you know that a servlet has two methods the container calls when the servlet is loaded and shut down, respectively. These methods are called init( ) and destroy( ), and they allow the servlet to initialize instance variables when it’s loaded and clean up when it’s shut down. As you already know, a JSP page is turned into a servlet, so it has the same capability. However, with JSP, the methods are called jspInit( ) and jspDestroy( ) instead.

Again, I recommend that you don’t declare any instance variables for your JSP pages. If you follow this advice, there’s also no reason to declare the jspInit( ) and jspDestroy( ) methods. But I know you’re curious, so here’s an example of how they can be used.

Expanding on Example 16-3, the jspInit( ) method can set an instance variable to a java.util.Date( ) object, which represents the date and time when the page was initialized. This variable can then be used in the page to show when the counter was started:

<%@ page language="java" contentType="text/html" %>
<%@ page import="java.util.Date" %>
<%! 
                  int globalCounter = 0; 
                  java.util.Date startDate;
  
                  public void jspInit(  ) {
                  startDate = new java.util.Date(  );
                  }
  
                  public void jspDestroy(  ) {
                  ServletContext context = getServletConfig().getServletContext(  );
                  context.log("test.jsp was visited " + globalCounter +
      " times between " + startDate + " and " + (new Date(  )));
                  }
                  %> <html> <head> <title>A page with a counter</title> </head> <body ...

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