Introduction to Servlets

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This document introduces the basics about servlets:

What servlets are
What makes them attractive to use
What advantages are gained by using the Servlet API

About Servlets

Servlets provide a Java^TM-based solution used to address the problems currently associated with doing server-side programming, including inextensible scripting solutions, platform-specific APIs, and incomplete interfaces.

Servlets are objects that conform to a specific interface that can be plugged into a Java-based server. Servlets are to the server-side what applets are to the client-side -- object bytecodes that can be dynamically loaded off the net. They differ from applets in that they are faceless objects (without graphics or a GUI component). They serve as platform-independent, dynamically-loadable, pluggable helper bytecode objects on the server side that can be used to dynamically extend server-side functionality.

For example, an HTTP servlet can be used to generate dynamic HTML content. When you use servlets to do dynamic content you get the following advantages:

they're faster and cleaner than CGI scripts
they use a standard API (the Servlet API)
they provide all the advantages of Java (run on a variety of servers without needing to be rewritten)

The Attractiveness of Servlets

There are many features of servlets that make them easy and attractive to use. Servlets are:

easily configured using the GUI-based Administration Tool.
loaded and invoked from a local disk or remotely across the network.
linked together, or chained, so that one servlet can call another servlet, or several servlets in sequence.
called dynamically from within HTML pages, using server-side include tags.
secure - even when downloading across the network, the servlet security model and servlet sandbox protect your system from unfriendly behavior.

(NOTE: Security in the Java^TM Web Server^TM is provided by combining the code-signing facility of JDK^TM 1.1 and the Access Control List implementation of the Server Toolkit. This allows servlet classes, or servlet JAR files, to be signed. The signers are then assigned permissions in an access control list. For more information on servlet security, see Security Administration for Java Web Server).

The Advantages of the Servlet API

One of the great advantages of the Servlet API is protocol independence. It assumes nothing about:

the protocol being used to transmit on the net
how it is loaded
the server environment it will be running in

These qualities are important, because it allows the Servlet API to be embedded in many different kinds of servers. There are other advantages to the Servlet API as well. These include:

it's extensible - you can inherit all your functionality from the base classes made available to you.
it's simple, small, and easy to use.

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