What is TomCat?

• TomCat is a servlet container.

• Java provides a number of ways to write server-side Java programs. Two main ones are Servlets and Java Server Pages (JSP).

  Servlets

  A Servlet is a class that extends the HTTPServlet class. To use it, import the following packages:

  
      import javax.servlet.*;
      import javax.servlet.http.*;
  

  A Servlet is Java code to implement a web-based application.

• It runs on the Server, and generates HTML code as its output.

• Multiple threads are run on the Servlet in order to process mutliple client requests.

• Data is sent and must be received using one of two methods:
  • GET - the data is read from an environment variable.
  • POST - the data is read from standard in.

  JSP

• JSP allows you to write HTML code with embedded Java. When the JSP code is executed, it is compiled into a Servlet, which is then executed.

• Both of these require that the Servlet be run in a container, which is what TomCat is.

• Note that when you want to run, the URL that is used includes the port number.

• This is because the default port number (which is not typically specified) accesses the default HTTP server.

• When you run startup at the command prompt, you are causing the TomCat server to run. It listens for requests on port 8080.

• To run the application, you type this URL:

  http://localhost:8080/YourApp

• This indicates to running the http protocol, but instead of communicating with the default HTTP server, use port 8080, which is TomCat.