Introduction to Java EE technology - Servlet - Servlet Container - Servlet API

1. Introduction to
Java Enterprise Edition
● First steps with Servlet Technology.
Servlet Container & Application Server
●
Fernando Gil
Fernando Gil
lobho.gil@gmail.com
lobho.gil@gmail.com
Marzo 2012
Marzo 2012

2. Introduction
● The goal of this course is to explain you how can
you start to develop Java EE applications.
● We will accomplished our goals by presenting the
theory behind the concepts of Servlets and
JavaServer Pages.
● Using JBoss AS or similar we'll present practical
exercises to support all the knowledge obtained.

3. A Servlet is...
● A server-side entity.
● A Java programming language class used to extend the
capabilities of servers that host applications access via a
request-response programming model.
● The Java counterpart to non-Java dynamic Web content
technologies such as CGI and ASP.NET.

4. Server Responsibilities
● Every server has two main responsibilities:
● Handle Client Requests.
● Create a response to the clients. In the
case of HTTP servers that host web
applications this could be a difficult task
because they need to create dynamic web
contents, which may include complicated
tasks such as retrieving information from
the database, apply business rules and
present the information in specific views.
The best way to perform this responsibility
is create server extensions that we know as
Servlets.

5. Servlet Container
● To deploy and run a servlet, a Web server uses a separate
module. This specialized module is called Web container or
servlet container and is responsible for managing the lifecycle of
servlets, mapping a URL to a particular servlet and ensuring that
the URL requester has the correct access rights.
● The next picture shows how different components fit together.
The file system stores HTML files, the Servlet container execute
the Servlets, and business data is in the database. The Web
browser sends requests to the Web server. If the target is an
HTML file, the server handles it directly but If the target is a
servlet then the server delegates the request to the servlet
container, once there, the servlet can use the file system and
database to generate dynamic output.

6. All pieces together

7. Servlet container types
Conceptually, a servlet container is a part of the web server, even though
it may run in a separate process. We can classify the servlet container in
three types:
● Standalone: Are typically Java-based servers where the servlet
container and the web server are integral part of a single program.
One common example is Tomcat running by itself.
● In-process: The servlet container is separated from the web server,
because is a different program, but runs within the address space of
the main server as a plug-in. One example is Tomcat running inside
JBoss.
● Out-of-process: The servlet container and the web server are
different programs and both run in a different process. To perform
communications between them, the web server uses a plug-in
usually provided by the servlet container vendor.

9. Relationship between Servlet
Container & Servlet API
● Java's Servlet specification provides a standard and
platform-independent framework for communication
between servlets and their containers. All the servlet
containers must provide this API.
● This framework is made up of a set of interfaces an
classes which are collectively called the Servlet
Application Programming Interfaces.
● The Servlet API is divided into two packages:
javax.servlet and javax.servlet.http

10. javax.servlet
● This package contains the generic interfaces and classes that are
independent of any protocol.
Name Brief Description
Servlet interface This is the central interface in the API. Every class
must directly or indirectly implements this interface.
GenericServlet It is an abstract class that provides implementation
class for all the methods except the service() method of the
Servlet interface
ServletRequest Provides a generic view of the request that was sent
interface by a client and defines methods that extract
information form the request.
ServletResponse Provides a generic way of sending responses to the
interface client.

11. javax.servlet.http
● This package contains the basic functionality required for HTTP servlets.
Interfaces an classes in this package extend the corresponding interfaces an
classes of the javax.servlet package.
Name Brief Description
HttpServlet class Is an abstract class that extends GenericSevlet. It
adds a new service() method.
HttpServletRequest Extends ServletRequest and provides an HTTP-
interface specific view of the request. It defines methods
that extract information such as HTTP headers an
cookies from the request.
HttpServletResponse Extends ServletResponse and provides an HTTP-
interface specific way of sending responses. It defines
methods that assist in setting information, such as
HTTP headers and cookies into the response.

12. Advantages of the Servlet API
Advantage Description
Flexibility If we need to extend the server
functionality all we have to do is write a
new servlet specific for that requirement
without modifying the server itself.
Separation of The server only needs to worry about
responsibilities network and communication, while the
servlet interprets and response to every
client request.
Java language Java programmers do not need to lear a
new language.
Portability We can write a servlet in one container,
and deploy it in another.

13. Disadvantages of the Servlet API
● One disadvantage, rather restriction is that
you have to stick to the rules set for the
framework to make the container happy.
● Theoretically using the API you can write
servlets for almost any kind of protocol but,
by the moment, the Servlet specification
only demands support to HTTP.