MC365 Application Servers, Servlets, and Java Server Pages (JSP’s): Tomcat

Today We Will Cover: What is an application server? How do servlets and jsp’s work with an application server? Introduce the Tomcat application server.

What is an application server? It is easier to answer this question by looking at the history of dynamic web pages and the factors that led to the development of the application server. Years ago dynamic web pages were generated using a technology called CGI (Common Gateway Interface). –This was usually a program written in C, Perl or some other similar language. –The web server was configured to recognize certain http requests and execute that program. –This worked well for a while.

Disadvantages of CGI As the web became more and more popular, the load placed on these web servers and CGI programs increased. One of the major inefficiencies of CGI programming is that every time a request is made for that program, a new instance is kicked off by the web server. For popular websites, this can quickly use up all of the resources on that server causing delays or even crashes. In the late 1990s, the popularity of the Internet was increasing at a remarkable rate. At the same time a new language was also become more and more popular…Java.

Benefits of Java Servlets The creators of Java came up with an interesting solution to the CGI problem – Java servlets. Servlets are a type of Java program similar to applications and applets. –We will go over servlets in more detail in the next class. They are Java’s answer to server-side programming.

Benefits of Java Servlets So, what makes servlets better than CGI? –Servlets are multi-threaded First and foremost, servlets take advantage of Java’s concept of threads. This is a major advantage. When a request is made to the web server calling for it to execute the java program, the Java program can just kick off a new thread instead of instantiating a new instance of the program. This saves a tremendous amount of server resources. –Portable As with all other java programs, servlets can run on multiple platforms. Remember Sun’s promise of write once, run anywhere philosophy. –Industry standard Java is pretty well established as the language of choice for server-side programming for the web.

So, again what is an application server? Ok, getting back to the original question. –Unlike CGI programs, Java servlets can not be called directly by the web server. They need a container as defined by the J2EE standard. –This container is called an application server. –The application server, or app server as it is often called, works in concert with the web server. Actually, most of today’s app servers have built-in web servers. –This is the way it works:

How the Process Works The user submits an http request via a web browser (like Netscape or IE). The http request is received by the web server, which has been configured to send certain requests to the application server. The application server receives these special requests. It knows which servlet to execute based on the http request (the app server has its own configuration). The servlet is executed, does its thing, and generates a response to the user in html format.

How do JSP’s fit in? –The Java servlet can produce the HTML response directly or it can call a Java Server Page (JSP) to generate the HTML. –Why would you want to use a JSP? –The main reason for using JSP’s is to separate the presentation from the business logic. –Servlets are generally responsible for performing the business logic. –JSP’s are generally responsible for presentation. –If you generate the HTML directly in the servlet, any changes to design need a programmer. –If you use a JSP, many design changes can be done by the UI team directly. –We will cover JSP’s in a lot more detail in a week.

The Tomcat Application Server –Application servers are basically programs (just as web servers are). –Different companies have developed a variety of application servers. Here are the industry leaders: –WebLogic –IBM’s WebSphere –Tomcat –WebLogic and WebSphere are marketed for large-scale enterprises. –They are industrial strength packages but they are very expensive. –Together they own most of the app server market share.

The Tomcat Application Server –Tomcat is an app server produced by the Jakarta project. –It is free and open source. –It is a very good app server and is a favorite among many smaller organizations that don’t need many of the bells and whistles of the other two and/or can’t afford them. –It is a great tool to learn on. Once you become familiar with one app server, it is much easier to learn the others. –Tomcat is much easier to manage than many of the other application servers.

So how do you set up Tomcat? –Tomcat can run on many different platforms. In this class we will go over how to install Tomcat on the Windows operating system. –You are free to install it on another operating system if you want. Once installed, management of the app server is relatively the same regardless of the OS. –However, because most students here run Windows, that is the OS we will use in class.

Installing Tomcat? –Go to Click on the tomcat exe download link and save it to your system. Execute the executable.

Verify that your installation is running successfully –Open a web browser. –Go to –Click on the Servlet Examples link. –Execute the Hello World example. –You should see Hello World!