Programming Jakarta Struts, 2nd Edition [Electronic resources] نسخه متنی

1.3 JavaServer Pages

The first thing to understand about JavaServer
Pages is that it's a natural extension to the Java
Servlet technology. In fact, after some preprocessing by a
translator, JSP pages end up being nothing more than Java servlets.
This is a point that many beginning developers have a hard time
understanding. JSP pages are text documents that have a
.jsp extension and contain a combination of
static HTML and XML-like tags and
scriptlets. The tags and scriptlets encapsulate the logic that
generates the content for the pages. The .jsp
files are preprocessed and turned into .java
files. At this point, a Java compiler compiles the source and creates
a .class file that can be executed by a servlet
container.

The translator that turns the .jsp file into a
.java file takes care of the tedious work of
creating a Java servlet from the JSP page. Figure 1-2 illustrates how a JSP page is translated and
compiled into a servlet.

Figure 1-2. A JSP page is translated and compiled into a Java servlet

JSP technology has become an extremely popular solution for building
web applications using the Java platform. JSP offers several
advantages over its competitors:

• JSP is a specification, not a product. Developers are able to choose
  a "best of breed" approach.

• JSP pages are compiled, not interpreted, which can lead to better
  performance.

• JSP pages support both scripting and access to the full Java language
  and can be extended through the use of custom tags.

• JSP pages share the Write Once, Run
  Anywhere™ characteristics of Java technology.

As mentioned in the previous section, one of the limitations of using
hardcoded HTML inside of servlets is the problem of separating page
design and application logic programming responsibilities. This
separation is easier with JSP pages, because the HTML designers are
free to create web pages with whatever tools they choose (many of
today's popular tools are capable of working with
JSP and custom tags). When they are comfortable with the page layout,
the JSP developers can insert JSP scriptlets and custom tags and save
the files with a .jsp extension.
That's pretty much all there is to it. When the time
comes to change either the page layout or page logic, the developer
modifies the JSP page as needed and allows it to be recompiled
automatically.

Together, JSP pages and servlets are an attractive alternative to
other types of dynamic web programming. Because both are based on the
Java language, they offer platform-independence, extensibility into
the enterprise, and, most importantly, ease of development.