Thursday, October 24, 2013

Apache Tomcat - Tutorial

Apache Tomcat
This article describes the installation and usage of Apache Tomcat for Java web development. Tomcat version 7.x is used in this tutorial.

1. Apache Tomcat

Apache Tomcat is a webcontainer which allows to run servlet and JavaServer Pages based web applications. Most of the modern Java web frameworks are based on servlets and JavaServer Pages and can run on Apache Tomcat, e.g. JavaServer Faces, Struts, Spring.
Apache Tomcat also provides by default a HTTP connector on port 8080, e.g. Tomcat can also be used as HTTP server even though the performance of Tomcat is not as good as the performance of the Apache HTTP server.

2. Installation

2.1. Ubuntu Linux

For Ubuntu you can install Tomcat via the following commands.
apt-get install tomcat7
apt-get install tomcat7-admin
apt-get install tomcat7-docs
apt-get install tomcat7-examples

2.2. Windows

Download the Windows installer for Tomcat7 from the Apache Tomcat Homepage and run the installer.

3. Managing Apache Tomcat

3.1. Start Tomcat on Ubuntu (Linux)

In Ubuntu the Tomcat server is started automatically. To restart Tomcat use the following command.
# Restart
sudo /etc/init.d/tomcat7 restart

# Stop
sudo /etc/init.d/tomcat7 stop

3.2. Start Tomcat on Windows

To start Tomcat use tomcat7.exe in the bin directory.

3.3. Test Tomcat

The default port for Tomcat is 8080. After starting Tomcat on your local you can validate if Tomcat is running the URL: http://localhost:8080.

3.4. Admin console

Tomcat provides a webbased adminstration console which can be started via the following link.
http://localhost:8080/manager/html 
The default user for the administration console of Tomcat is called admin with the admin password.
The available users can be found in the /conf/tomcat-users.xml directory of the Tomcat installation.
On Ubuntu the user for the administrator console is not created automatically, you have to add the user entry manually to the /etc/tomcat7/tomcat-users.xml . The following listing gives an example for a user. To get more information try to login and see the resulting error message.
<role rolename="manager-gui" />
<user username="tomcat" password="s3cret" roles="manager-gui" />

3.5. Deployment

The standard deployment format for webapplications is a .war file. If you have create a war application just put this application into the webapps folder. The next time tomcat starts it will unpack the war and make the application available.
Web applications may require external libraries. Typically web application contain there own libraries but if you want to make certain libraries available for all applications you can put them into the folder "lib" and a subfolder below "lib". These libraries are then available for all web applications.

4. Developing Java web applications

After going through the setup you properly want to learn how to develop servlets and JSP on installation directory. Please see Servlets and JSP development - Tutorial

5. Tomcat as HTTP Server

contains also a HTTP connector which can be used to serve static HTML pages. The standard directory which will be served is below the Tomcat webapps/ROOT below the installation directory. Place static content into this directory.
To allow directory browsing via Apache Tomcat change the listings parameter in the fileconf/web.xml from false to true.
<servlet>
<servlet-name>default</servlet-name>
<servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
<init-param>
<param-name>debug</param-name>
<param-value>0</param-value>
</init-param>
<init-param>
<param-name>listings</param-name>
<param-value>true</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>

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