Java Reference
In-Depth Information
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Developing e-commerce “store fronts” will become one of the most common uses for
Java servlets. A servlet can build an online catalog based on the contents of a database. It
can then present this catalog to the customer using dynamic HTML. The customer will
choose the items to be ordered, enter the shipping and billing information, and then sub-
mit the data to a servlet. When the servlet receives the posted data, it will process the
orders and place them in the database for fulfillment. Every one of these processes can
easily be implemented using Java servlets.
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Servlets can be used to deploy Web sites that open up large legacy systems on the
Internet. Many companies have massive amounts of data stored on large mainframe sys-
tems. These businesses do not want to re-architect their systems, so they choose to pro-
vide inexpensive Web interfaces into them. Because you have the entire JDK at your
disposal and security provided by the Web server, you can use servlets to interface into
these systems using anything from TCP/IP to CORBA.
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Servlets also make very good HTTP-enabled clients to Enterprise Java Bean (EJB) appli-
cations. Using servlets as clients to EJB applications creates very secure Web applica-
tions that are able to handle very high volumes.
These are just a few examples of the power and practicality of using Java servlets. Servlets are
very viable options for most Web applications.
Java Servlet Alternatives
Some alternatives to using Java servlets are CGI, proprietary server APIs, server-side
JavaScript, or even Microsoft's Active Server Pages. All these are viable solutions, but they
each have their own set of problems. The following sections examine some of these issues.
Common Gateway Interface
The Common Gateway Interface (CGI) is one of the most common server-side solutions used to
develop Web applications. A CGI application is an independent module that receives requests
from a Web server. The application processes the data it receives and sends it back to the server,
typically as HTML. The server then sends the data to the browser. CGI has become a standard
that is used by most of today's Web servers. Figure 2.2 shows the interaction between the
browser, Web server, and CGI application when you implement this type of solution.
Although CGI is a widely used solution to dynamic Web development, it is also a very prob-
lematic solution. The following are some of the most common problems with CGI:
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A Web server creates a new process every time it receives a CGI request. This results in
a slower response time, because the server must create and initialize a new address space
for every process. You can also face the problem of running out of processes. Most
