Intro to Servlets

Lec 26

Web-Based Enterprise Applications in Java

Figure shows a simplified view of one application and its layers.

Java Servlets

Client/ browser

ServerRequest

Response

Servlet

JVM

Extends the functionality of the server byGenerating HTML pages dynamically

What Do They Do?

Anything that java can do (e.g. connect to database services)

Handle data/requests sent by users (clients)

Create and format results

Send results back to user

Java Servlets

Advantages over other SSP technologies: Can use the Java APIs e.g. JDBC. Persistent between invocations, avoiding process

instantiations. Portable across operating systems and servers. Good security. Is integrated closely with the J2EE environment.

Software Requirements

Software Requirements

To use Java servlets, following softwares will be needed

J2SE

Additional J2EE based libraries for servlets such as servlet-api.jar, jsp-api.jar. You can download these APIs separately but they are also available with the web server you’ll be using.

A capable servlet web engine (web server)

Jakarta Servlet Engine (Tomcat) Jakarta is an Apache project

Tomcat is one of its subprojects

Tomcat is the official reference implementation for the Java servlet and JavaServer pages technologies (according to Sun’s specifications)

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

Environment Setup

Environment Setup

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

1. Download the Apache Tomcat Server

From the http://jakarta.apache.org

Download the zip file for the current release of

Jakarta Tomcat

For windows, there is also a .exe installer

2. Install Tomcat

Installing .zip file Unzip the file into a location (e.g. C:\) The zip file had embedded subdirectories

(e.g., jakarta-tomcat-5.5.9).

C:\ jakarta-tomcat-5.5.9 generally referred as install_dir

Installing .exe file Check the handouts

3. Set the JAVA_HOME variable

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

JAVA_HOME = c:\j2sdk1.5.0

4. Set the CATALINA_HOME variable

Set the CATALINA_HOME environment variable to refer to the top-level directory of the Apache Tomcat installation, not the bin subdirectory

CATALINA_HOME = c:\jakarta-tomcat-5.5.9

5. Set the CLASSPATH variable

Since servlets and JSP are not part of the J2SE, javac doesn’t know about the servlet and jsp classes

The standard Tomcat locations for these files are install_dir/common/lib/servlet-api.jar install_dir/common/lib/jsp-api.jar

You need to include both files in your CLASSPATH

6. Test the Server

Before making your own Servlets and JSP, verify that the server can start

Run install_dir/bin/startup.bat

Enter the URL http://localhost:8080 in your browser and make sure you will get the Tomcat homepage

Lets do it LIVE

Tomcat Directory Structure

my-app