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# Servlet Introduction ## What is a Servlet? A Java Servlet is a program that runs on a web server or application server. It acts as an intermediary between requests from web browsers or other HTTP clients and databases or applications on the HTTP server. Using Servlets, you can collect user input from web page forms, present records from databases or other sources, and dynamically create web pages. Java Servlets generally achieve similar results to programs implemented using CGI (Common Gateway Interface). However, compared to CGI, Servlets have the following advantages: * Performance is significantly better. * Servlets execute within the address space of the web server. This eliminates the need to create a separate process to handle each client request. * Servlets are platform-independent because they are written in Java. * The Java security manager on the server enforces a set of restrictions to protect resources on the server computer. Therefore, Servlets are trustworthy. * The full functionality of the Java class libraries is available to Servlets. They can interact with applets, databases, or other software via sockets and RMI mechanisms. ## Servlet Architecture The following diagram shows the position of a Servlet in a web application.  ## Servlet Tasks Servlets perform the following main tasks: * Read explicit data sent by the client (browser). This includes HTML forms on web pages, or forms from applets or custom HTTP client programs. * Read implicit HTTP request data sent by the client (browser). This includes cookies, media types, compression formats that the browser can understand, etc. * Process the data and generate results. This process may require accessing a database, performing RMI or CORBA calls, invoking web services, or directly computing the corresponding response. * Send explicit data (i.e., documents) to the client (browser). The format of the document can be varied, including text files (HTML or XML), binary files (GIF images), Excel, etc. * Send implicit HTTP responses to the client (browser). This includes telling the browser or other client the type of document being returned (e.g., HTML), setting cookies and cache parameters, and other similar tasks. ## Servlet Packages Java Servlets are Java classes that run on a web server with an interpreter that supports the Java Servlet specification. Servlets can be created using the **javax.servlet** and **javax.servlet.http** packages, which are standard components of Java Enterprise Edition, an extended version of the Java class library that supports large-scale development projects. These classes implement the Java Servlet and JSP specifications. At the time of writing this tutorial, the corresponding versions are Java Servlet 2.5 and JSP 2.1. Java Servlets are created and compiled like any other Java class. After you install the Servlet packages and add them to your computer's Classpath, you can compile Servlets using the JDK's Java compiler or any other compiler. ## What's Next? Next, this tutorial will guide you step-by-step through setting up your Servlet environment to start using Servlets. So, fasten your seatbelts and join us on this Servlet learning journey! We believe you will enjoy this tutorial.