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Web Design & Development ­ CS506
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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:
1
Download the Apache Tomcat Server
2
Install Tomcat
3
Set the JAVA_HOME variable
4
Set the CATALINA_HOME variable
5
Set the CLASSPATH variable
6
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 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
next
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
Internet Options 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
Internet Options 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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