Java Servlets

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Web Design & Development CS506

Lesson 26

Java Servlets

Servlets are java technology's answer to CGI programming. CGI was widely used for generating dynamic

content before Servlets arrived. They were programs written mostly in C,C++ that run on a web server and

used to build web pages.

As you can see in the figure below, a client sends a request to web server, server forwards that request to a

servlet, servlet generates dynamic content, mostly in the form of HTML pages, and returns it back to the

server, which sends it back to the client. Hence we can say that servlet is extending the functionality of the

webserver (The job of the earlier servers was to respond only to request, by may be sending the required

html file back to the client, and generally no processing was performed on the server)

What Servlets can do?

Servlets can do anything that a java class can do. For example, connecting with database,

reading/writing data to/from file etc.

Handles requests sent by the user (clients) and generates response dynamically (normally HTML

pages).

The dynamically generated content is send back to the user through a webserver (client)

Servlets vs. other SSP technologies

The java's servlet technology has following advantage over their counter parts:

Convenient

Servlets can use the whole java API e.g. JDBC. So if you already know java, why learn Perl or C.

Servlets have an extensive infrastructure for automatically parsing and decoding HTML form data,

reading and sending HTTP headers, handling cookies and tracking session etc and many more utilities

Efficient

With traditional CGI, a new process is started for each request while with servlets each request is handled

by a lightweight java thread, not a heavy weight operating system process. (more on this later)

Powerful

Java servlets let you easily do several things that are difficult or impossible with regular CGI. For example,

servlets can also share data among each other

Portable

Since java is portable and servlets is a java based technology therefore they are generally portable across

web servers

Inexpensive

There are numbers of free or inexpensive web servers available that are good for personal use or low

volume web sites. For example Apache is a commercial grade webserver that is absolutely free. However

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some very high end web and application servers are quite expensive e.g BEA weblogic. We'll also use

Apache in this course

Software Requirements

To use java servlets will be needed

J2SE

Additional J2EE based libraries for servlets such as servlet-api.jar and jsp-api.jar. Since these

libraries are not part of J2SE, you can download these APIs separately. However these APIs are

also available with the web server you'll be using.

A capable servlet web engine (webserver)

Jakarta Servlet Engine (Tomcat)

Jakarta is an Apache project and tomcat is one of its subprojects. Apache Tomcat is an open source web

server, which is used as an official reference implementation of Java Servlets and Java Server Pages

technologies.

Tomcat is developed in an open and participatory environment and released under the Apache software

license

Environment Setup

To work with servlets and JSP technologies, you first need to set up the environment. Tomcat installation

can be performed in two different ways (a) using .zip file (b) using .exe file. This setup process is broken

down into the following steps:

Download the Apache Tomcat Server

Install Tomcat

Set the JAVA_HOME variable

Set the CATALINA_HOME variable

Set the CLASSPATH variable

Test the Server

Environment Setup Using .zip File

Let's take a detail look on each step and get some hands on experience of environment setup.

1. Download the Apache Tomcat Server

From the http://tomcat.apache.org, download the zip file for the current release (e.g. jakarta-tomcat-

5.5.9.zip or any latest version) on your C:\ drive. There are different releases available on site. Select to

download .zip file from the Binary Distributions Æ core section.

Note: J2SE 5.0 must be installed prior to use the 5.5.9 version of tomcat.

2. Installing Tomcat using .zip file

-Unzip the file into a location (e.g. C:\). (Rightclick on the zip file and select unziphere option )

-When the zip file will unzipped a directory structure will be created on your computer such as:

-The C:\jakarta-tomcat-5.5.9 folder is generally referred as root directory or CATALINA_HOME

Note: After extraction, make sure C:\jakarta-tomcat-5.5.9 contains a bin subdirectory. Sometimes

students create their own directory and unzip the file there such as C:\jakarta-tomcat-5.5.9\jakarta-

tomcat-5.5.9.This causes problems while giving path information

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3. Set the JAVA_HOME variable

JAVA_HOME indicates the root directory of your jdk. Set the JAVA_HOME environment

variable to tell Tomcat, where to find java

This variable should list the base JDK installation directory, not the bin subdirectory

To set it, right click on My Computer icon. Select the advanced tab, a System Properties window

will appear in front of you like shown below. Select the Environment Variables button to proceed.

On clicking Environment Variable button, the Environment Variables window will open as shown

Create a new User variable by clicking New button as shown above, the New User Variable

window will appear

Set name of variable JAVA_HOME

The value is the installation directory of JDK (for example C:\ProgramFiles\j2sdk_nb\j2sdk1.4.2).

This is shown below in the picture. Please note that bin folder is not included in the path.

Press Ok button to finish

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4. Set the CATALINA_HOME variable

CATALINA_HOME is used to tell the system about the root directory of the TOMCAT. There are various

files (classes, exe etc) needed by the system to run. CATALINA_HOME is used to tell your system (in this

case your web server Tomcat) where the required files are.

To Set the CATALINA_HOME environment variable, create another User Variable.

Type CATALINA_HOME as the name of the environment variable.

Its value should be the path till your top-level Tomcat directory. If you have unzipped the Tomcat

in C drive. It should be C:\jakarta-tomcat-5.5.9.This is shown below:

Press Ok button to finish

Note:

To run Tomcat (web server) you need to set only the two environment variables and

these are JAVA_HOME & CATALINA_HOME

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5. Set the CLASSPATH variable

Since servlets and JSP are not part of the Java 2 platform, standard edition, you have to identify the

servlet classes to the compiler. The server already knows about the servlet classes, but the compiler

(i.e., javac) you use for compiling source files of servlet does not. So if you don't set your

CLASSPATH, any attempt to compile servlets, tag libraries, or other classes that use the servlet API

will fail with error messages about unknown classes.

To Set the CLASSPATH environment variable, create another User Variable.

Type CLASSPATH as the name of the environment variable.

Its value should be the path for servlet-api.jar and jsp-api.jar. These file can be found on following

path:

C:\jakarta-tomcat-5.5.9\common\lib\servlet-api.jar

C:\jakarta-tomcat-5.5.9\common\lib\jsp-api.jar

Both these api's are specified as values with semicolon between them. Remember to add

semicolon dot semicolon (;.;) at the end too. For example

Classpath = C:\jakarta-tomcat-5.5.9\common\lib\servlet-api.jar;C:\jakarta-tomcat

5.5.9\common\lib\jsp-api.jar;.;

This is also shown in the figure below

-- Press OK button to finish the setting of CLASSPATH variable

6. Test the server

Before making your own servlets and JSP, verify that the server is working properly. Follow these steps

in order to do that:

Open the C:\jakarta-tomcat-5.5.9\bin folder and locate the startup.batfile.

Double clicking on this file will open up a DOS window, which will disappear, and another DOS

window will appear, the second window will stay there. If it does not your paths are not correctly

set.

Now to check whether your server is working or not, open up a browser window and type

http://localhost:8080. This should open the default page of Tomcat as shown in next diagram:

Note: If default page doesn't displayed, open up an internet explorer window, move on to Tools Æ

Internet Options Æ Connections LAN Settings. Make sure that option of "Bypass proxy server

for local addresses" is unchecked.

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There is another easier way to carry out the environment setup using .exe file. However, it is strongly

recommended that you must complete the environment setup using .zip file to know the essential

fundamentals.

Environment Setup Using .exe File

Let's look at the steps involved to accomplish the environment setup using .exefile.

1. Download the Apache Tomcat Server

From the http://tomcat.apache.org, download the .exe file for the current release (e.g. jakarta-tomcat-

5.5.9.zip) on your C:\ drive. There are different releases available on site. Select to download Windows

executable (.exe) file from Binary Distributions Core section.

Note: J2SE 5.0 must be installed to use the 5.5.9 version of tomcat.

2. Installing Tomcat using .exe file

-Run the .exefile by double clicking on it.

-Moving forward in setup, you will reach to the following window -Select install type "Full" and

press Next button to proceed.

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-Choose the folder in which you want to install Apache Tomcat and press Next to proceed.

-The configuration window will be opened. Leave the port unchanged (since by default web servers run on

port 8080, you can change it if you really want to). Specify the user name & password in the specified

fields and press Next button to move forward. This is also shown in the diagram coming next:

-The setup will automatically select the Java Virtual Machine path. Click Install button to move ahead.

-Finish the setup with the Run Apache Tomcat option selected. It will cause the tomcat server to run in

quick launch bar as shown in diagram below. The Apache Tomcat shortcuts will also added to

Programs menu.

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-Double clicking on this button will open up Apache Tomcat Properties window. From here you can start

or stop your web server. You can also configure many options if you want to. This properties window

is shown below:

3. Set the JAVA_HOME variable

Choosing .exe mode does not require completing this step.

4. Set the CATALINA_HOME variable

Choosing .exe mode does not require completing this step.

5. Set the CLASSPATH variable

Same as step 5 of .zip installation mode

6. Test the server

If tomcat installation is made using .exe file, follow these steps

-Open the Apache Tomcat properties window by clicking on the Apache Tomcat button from Quick

Launch.

-Start the tomcat server if it is not running by clicking on Start button.

-Open up a browser window and type http://localhost:8080. This should open the default page of Tomcat

as shown in the next diagram:

Note:

If default page doesn't displayed, open up an internet explorer window, move on to Tools Æ

Internet Options Æ Connections LAN Settings. Make sure that option of "Bypass proxy server for

local addresses" is unchecked.

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References:

. Java, A Lab Course by Umair Javed

. Java Servlet & JSP tutotrial http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/

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