We have already seen how to embed Java expressions in JSP pages by putting them between the <%= and %> character sequences.

But it is difficult to do much programming just by putting Java expressions inside HTML.

JSP also allows you to write blocks of Java code inside the JSP.  You do this by placing your Java code between <% and %> characters (just like expressions, but without the = sign at the start of the sequence.)

This block of code is known as a "scriptlet".  By itself, a scriptlet doesn't contribute any HTML (though it can, as we will see down below.)  A scriptlet contains Java code that is executed every time the JSP is invoked.

Here's the outline of a basic servlet that handles GET requests. GET requests, for those unfamiliar with HTTP, are requests made by browsers when the user types in a URL on the address line, follows a link from a Web page, or makes an HTML form that does not specify a METHOD. Servlets can also very easily handle POST requests, which are generated when someone creates an HTML form that specifies METHOD="POST". We'll discuss that in later sections.

This tag allows the developer to declare variables or methods.

Before the declaration you must have <%!

At the end of the declaration,the developer must have %>

Code placed in this tag must end in a semicolon ( ; ).

Declarations do not generate output so are used with JSP expressions or scriptlets.

Till now you learned about the JSP syntax, now I will show you how to create a simple dynamic JSP page that prints the current date and time. So the following code accomplish this:    

J2EE web components are either servlets or pages created using JSP technology (JSP pages). Servlets are Java programming language classes that dynamically process requests and construct responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.

Static HTML pages and applets are bundled with web components during application assembly but are not considered web components by the J2EE specification. Server-side utility classes can also be bundled with web components and, like HTML pages, are not considered web components.

As shown in Figure 1-3, the web tier, like the client tier, might include a JavaBeans component to manage the user input and send that input to enterprise beans running in the business tier for processing.