Just as a
web server needs a servlet container to
provide an interface to servlets, the server needs a JSP
container to process JSP pages. The JSP container is
responsible for intercepting requests for JSP pages. To process all
JSP elements in the page, the container first turns the JSP page into
a servlet (known as the [
JSP page implementation
class). The conversion is pretty straightforward; all
template text is converted to
statements similar to the ones in the handcoded servlet shown in
Example 3-1, and all JSP elements are converted to
Java code that implements the corresponding dynamic behavior. The
container then compiles the servlet class.
Converting the JSP page to a servlet and compiling the servlet form the translation phase. The JSP container initiates the translation phase for a page automatically when it receives the first request for the page. Since the translation phase takes a bit of time, the first user to request a JSP page notices a slight delay. The translation phase can also be initiated explicitly; this is referred to as precompilation of a JSP page. Precompiling a JSP page is a way to avoid hitting the first user with this delay. It is discussed in more detail in Chapter 16.
The JSP container is also responsible for invoking the JSP page implementation class (the generated servlet) to process each request and generate the response. This is called the request processing phase. The two phases are illustrated in Figure 3-3.
Figure 3-3. JSP ...