Apache Tomcat - web application server developed as part of the Apache project.
The Apache Tomcat® software is an open source implementation of the Java Servlet, JavaServer Pages, Java Expression Language and Java WebSocket technologies. This is one of the most popular Web containers. Tomcat is used in such JEE (J2EE) application servers as Apache Geronimo. It is also a very popular container for standalone applications (not requiring a full application server) written in the Spring Framework environment.
Tomcat's documentation: https://tomcat.apache.org/tomcat-8.5-doc/introduction.html
Key terms:
Document root - the main directory of the web application where its resources are located
Context path - the relative path to the server resources.
For example, if we put a web application in the /webapps/myapp directory, then we can get to it via the URL link http:/localhost/myapp, and its context path will be equal to /myapp.
WAR - is an extension of the package file containing the web application in ZIP format (short for the Web Archive). Typically, Java applications are packaged as WAR before deployment. Usually this file is created by the programming environment.
After uploading the WAR file, Tomcat unpacks it and saves its file in a new subdirectory in the webapps directory.
Exercise 1 - download Tomcat
Download the Tomcat binary distribution version 8.5 appropriate for the system you are using from the page https://tomcat.apache.org/download-80.cgi
Unpack the downloaded package to any place.
After unpacking, you will receive folder apache-tomcat-8.5.2.
Exercise 2 - Run the server
Start the Tomcat server using the /bin/startup.[sh|bat]
You should expect something like this:
Using CATALINA_BASE: /home/marcin/Downloads/apache-tomcat-8.5.35
Using CATALINA_HOME: /home/marcin/Downloads/apache-tomcat-8.5.35
Using CATALINA_TMPDIR: /home/marcin/Downloads/apache-tomcat-8.5.35/temp
Using JRE_HOME: /usr
Using CLASSPATH: /home/marcin/Downloads/apache-tomcat-8.5.35/bin/bootstrap.jar:/home/marcin/Downloads/apache-tomcat-8.5.35/bin/ tomcat-juli.jar
Tomcat started.Exercise 3 - check
Check if there is a sample application in the /webapps/sample/ directory.
Check if the application works. It should be available at: http://localhost:8080/sample/
If not, copy from the page
file Sample.war file to the /webapps/ directory
Restart Tomcat running
shutdown.[sh|bat]startup.[sh|bat]Check if both JSP page as well as Servlet works.
If "JSP page" does not work, then most likely you have to set the JAVA_HOME system variable to the JDK Java 8 path:
tomek@tomek-Lubuntu:~$ java -version
openjdk version "9-internal"
tomek@tomek-Lubuntu:~$ which java
/usr/bin/java
tomek@tomek-Lubuntu:~$ realpath /usr/bin/java
/usr/lib/jvm/java-9-openjdk-amd64/bin/java
tomek@tomek-Lubuntu:~$ ls /usr/lib/jvm/
java-1.8.0-openjdk-amd64 java-1.9.0-openjdk-amd64 java-8-openjdk-amd64 java-9-openjdk-amd64
tomek@tomek-Lubuntu:~$ export JAVA_PATH=/usr/lib/jvm/java-8-openjdk-amd64/Turn Tomcat off and on again and check if JSP started working correctly after setting JAVA_HOME:
Restart Tomcat running
shutdown.[sh|bat]startup.[sh|bat]If everything works, you should also have access to Tomcat's documentation, which is provided with it and by default provided by the server itself: http://localhost:8080/docs/index.html
Tomcat allows you to control access to applications launched on the server. Applications may (but do not have to) use the authentication method provided by Tomcat.
To allow access control, Tomcat uses a user database called Realm.
Realm contains a list of usernames, their passwords and roles.
Roles allow granting user rights to groups. They are similar to Linux groups of users.
One user can have several roles assigned.
Exercise 4 - configure access
Go to the default page provided with Tomcat: http://localhost:8080/
Try to view the server status by clicking on "Server Status"
A window asking for the username and password should appear.
For security reasons, Tomcat has no default users defined.
The roles that allow access to the Manager application are explained here: http://localhost:8080/docs/manager-howto.html#Configuring_Manager_Application_Access
When editing the /conf/tomcat-users.xml file, add the "guest" user, assign a password to it (it can be empty) and add the "manager-status" role:
<tomcat-users xmlns="http://tomcat.apache.org/xml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://tomcat.apache.org/xml tomcat-users.xsd"
version="1.0">
<!--
NOTE: By default, no user is included in the "manager-gui" role required
to operate the "/manager/html" web application. If you wish to use this app,
you must define such a user - the username and password are arbitrary. It is
strongly recommended that you do NOT use one of the users in the commented out
section below since they are intended for use with the examples web
application.
-->
<user username="guest" password="" roles="manager-status"/>
</tomcat-users>Try once again to log in to the application "manager/status".
Exercise 5a - manage, first step.
Manager is an application that allows you to manage Tomcat from the browser.
It is delivered by default launched with Tomcat.
Its part is the Server Status page that we visited in the previous task.
Try to visit the manager's website: http://localhost:8080/manager/html
Edit the /conf/tomcat-users.xml file again this time adding the admin user and assigning it a role that grants access to the manager page (what role should it have?).
Check if you have access to the manager after logging in as an admin.
If you are logged in as guest, try another browser or restart your browser (the whole application not only the tab).
Exercise 5b - manage, second step.
When we set up our server, we do not want users to have access to the sample applications provided with Tomcat, so it's worth turning them off.
One of such applications is the "sample" application that we opened in task 3. (http://localhost:8080/sample/) We will now try to disable this application.
Go to the manager's website: http://localhost:8080/manager/html
Stop ("Stop") the "sample" application that you opened in task 3. (http://localhost:8080/sample/)
Check if the site is available.
Stop and restart the server and check if the sample application is now available.
Use "Undeploy" to stop and remove our sample application.
Stop and restart the server and check if the sample application is now available.
Note that the application has been removed from the /webapps/sample directory and is not in the list of applications in the Tomcat manager.
Exercise 6 - Add new application to Tomcat
Adding new applications ("Deployment") is done automatically after copying them to the directory /webapps/ We can also do it from the Tomcat manager level.
Download files to your local hard drive
Extract to the directory and start Intellij
Choose Project -> Open and find the selected directory.
Select the Maven window to refresh (add a pom file if necessary) and run clean, install.
The target directory should appear in the project tree window and the file SimpleServlet-1.war should appear in it.
Copy this file to the Tomcat's webapps directory. Check if it works by going to http://localhost:8080/SimpleServlet-1/hello
If it does not work, enter the manager again, select WAR file to deploy by providing the above-mentioned file.
Exercise 7 - monitor
Look at the logs in /logs
Examine catalina.out file content.
Exercise 8 - crash
Add to application line
throw new OutOfMemoryError("blad");Build application with maven and deploy on the server. Run the application. See if you can find an error in the logs.
Exercise 9 - ports
By default, Tomcat works on port 8080. If any other process already occupies this port then we get an error when starting the server.
To change the port enter the settings in the file server.xml located in /conf/server.xml.
Change port to 8081, run Tomcat for the second time. Check in the browser whether applications are running on port 8081? Check what has happened in the logs.
Change ports in the server.xml file that need to be changed.
Re-start tomcat so that there are two separate instances.
Exercise 10 - debugging of the deployed application
Turn off Tomcat and turn on using
export JPDA_ADDRESS = 8000export JPDA_TRANSPORT = dt_socket/bin/catalina.sh jpda start
On windows:
set JPDA_ADDRESS = 8000set JPDA_TRANSPORT = dt_socketbin/catalina.bat jpda start
JPDA address is a port for listening when debugging the app running on Tomcat.
In intellij, select Run -> Debug then Edit Configurations, in the Select pane on the left plus and the Remote option.
In the newly opened window, change the port to 8000 and click on debug. From that moment on, you are connected to the debugger for a deployed Tomcat application.
Add a breakpoint in the 16th line of the SimpleServlet.java file and refresh the page. You should get a breakpoint on this line!