Tomcat is an open-source servlet container that also serves as a web server. At first glance, Tomcat seems to be a rather complicated topic, but it is not. Most Java programs run at the command line and perform some actions. Such programs implement one predefined function and then are no longer executed. Such programs usually have a main method that can be used to run them. A web program is designed to interact with a client. If there is a request from the client, it is processed and a response is sent to the user. If not, the program is idle. How to implement such logic in a standard application, given that you need to maintain sessions, accept HTTP requests, and so on? A while-true loop? No, you need a reliable solution. Tomcat exists for this purpose. In fact, it is a Java application that takes care of opening a port for interaction with the client, setting up sessions, the number of requests, the length of the header, and many other operations.
Tomcat has components that perform specific functions, and it’s worth knowing about them. Let’s take a closer look at them.
Catalina
This component allows developers to deploy their applications in a container. Catalina implements the Servlet API specification, the main web technology in Java web programming. In fact, Catalina is a servlet container inside Tomcat.
Jasper
Thanks to this component, the programmer uses JSP technology. These are like HTML files, but they have embedded Java code that can be executed when the page is sent to the user. This allows you to dynamically embed any data into the page. Jasper converts Java code to HTML, and also monitors changes and updates them automatically.
Coyote
This is an important component that listens to HTTP requests from the client on a specific port, provides this data for processing in the application, and returns responses to users. That is, Coyote implements the functionality of an HTTP server.
Installing Tomcat
To use Tomcat in Java, you need to install it on your system. You can read about how to install Tomcat in this article, which also covers other application servers. So, with Tomcat running and built into IDEA, you can try to build your first servlet.