Servlet Program in Java

Last Updated on April 26, 2023 by Prepbytes

Java Servlets are server-side programs written in Java and run on web servers. Servlets are used to create dynamic web pages, process and respond to user requests, and interact with databases. They provide a platform-independent, efficient, and scalable way to handle HTTP requests and responses. In this article, we will explore how to write a simple Servlet program in Java. To follow this article, you should have some basic knowledge of Java programming language and web development concepts.

What is a Servlet?

A Servlet is a Java program that runs on a web server and processes HTTP requests from web clients, such as web browsers. When a client sends an HTTP request to a web server, the server passes the request to a servlet that is capable of handling that type of request.

Once the servlet receives the request, it can perform a variety of actions, such as accessing a database, processing form data, or generating dynamic web content. Once the servlet has completed its processing, it returns a response to the client in the form of an HTTP response.

Servlets are designed to be highly flexible and configurable. They can be configured to handle different types of HTTP requests, such as GET, POST, and PUT requests. They can also be configured to handle different types of data, such as HTML, XML, and JSON.

Creating a Servlet Program in Java

Let’s take a closer look at the steps involved in creating a basic Servlet program in Java:

• Step 1 – Set up your development environment
  Before you can create a Servlet program in Java, you’ll need to set up your development environment. This typically involves installing the Java Development Kit (JDK) and a web server such as Apache Tomcat.

• Step 2 – Create a new Java class
  Once your development environment is set up, you can create a new Java class for your servlet. This class should extend the HttpServlet class, which is part of the Java Servlet API.

  Here’s an example of a basic servlet class:

  import javax.servlet.*;
  import javax.servlet.http.*;
  import java.io.*;
  
  public class MyServlet extends HttpServlet {
  
  }

  This class defines a new servlet called MyServlet.

• Step 3 – Override the doGet() or doPost() method
  The doGet() and doPost() methods are the two main methods used by servlets to handle HTTP requests. To create a basic servlet program, you’ll need to override one or both of these methods in your servlet class.

  Here’s an example of a basic doGet() method that sends a simple HTTP response:

  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      PrintWriter out = response.getWriter();
      out.println("Hello, World!");
  }

  This method sends a simple "Hello, World!" message back to the client as an HTTP response.

Deploying a Servlet

Once we have created a Servlet program in Java, we need to deploy it on a web server to make it accessible over the internet. To deploy a Servlet program in Java, you’ll need to follow these basic steps:

• Step 1 – Compile the Servlet program: Before you can deploy your Servlet program, you’ll need to compile the Java source code into bytecode. This can be done using the Java compiler, which is part of the Java Development Kit (JDK). The compiled bytecode should be packaged into a .war (Web Archive) file.

• Step 2 – Set up a web server: A web server such as Apache Tomcat is required to deploy a servlet program. If you don’t already have a web server set up, you can download and install Tomcat from the Apache website.

• Step 3 – Deploy the servlet program: Once you have a web server set up, you can deploy the servlet program by copying the .war file to the webapps directory of the Tomcat installation. The webapps directory is located in the Tomcat installation directory.

• Step 4 – Start the web server: After you have deployed the .war file, you’ll need to start the web server to make the servlet program available. This can be done by running the startup script (startup.bat on Windows, startup.sh on Unix) located in the bin directory of the Tomcat installation.

• Step 5 – Test the servlet program: Once the web server is running, you can test the servlet program by accessing it in a web browser. The URL for the servlet program will depend on the name of the .war file and the name of the servlet class.

  For example, if you have deployed a servlet program called "MyServlet" in a .war file called "myservlet.war", the URL to access the servlet might be:

   http://localhost:8080/myservlet/MyServlet

  In this example, "localhost" is the name of the machine running the web server, "8080" is the default port for Tomcat, "myservlet" is the name of the .war file, and "MyServlet" is the name of the servlet class.

In other words, deploying a servlet program in Java involves compiling the Java source code, setting up a web server such as Apache Tomcat, deploying the .war file to the webapps directory, starting the web server, and testing the servlet program by accessing it in a web browser. Once deployed, the servlet program can handle HTTP requests and generate dynamic web content.

Conclusion
In this article, we have explored the basics of writing a Servlet program in Java. We have seen how to create a Servlet class that handles HTTP requests and generates responses, and how to deploy our Servlet program on a web server. Servlets are a powerful tool for creating web applications in Java, and they provide a standard interface for communicating with web servers.

FAQs on Servlet Program in Java

Here are some frequently asked questions (FAQs) related to Servlet program in Java:

Q1: What is the difference between a Servlet and a JSP?
Ans: Servlets and JSPs (JavaServer Pages) are both used to create web applications in Java. However, Servlets are Java classes that handle HTTP requests and generate responses, while JSPs are templates that are used to generate HTML pages dynamically. Servlets are more suitable for handling complex business logic, while JSPs are better suited for creating user interfaces.

Q2: Can Servlets be used for handling non-HTTP requests?
Ans: No, Servlets are designed to handle HTTP requests only. If we need to handle non-HTTP requests, we can use other Java APIs such as RMI (Remote Method Invocation) or CORBA (Common Object Request Broker Architecture).

Q3: Can Servlets be multithreaded?
Ans: Yes, Servlets can be multithreaded. In fact, most web servers create a pool of threads to handle incoming requests, and each thread can handle multiple requests simultaneously.

Q4: How do Servlets handle sessions?
Ans: Servlets can use the HttpSession object to manage sessions. When a client makes a request to a Servlet, the Servlet can create a new session or retrieve an existing session using the request.getSession() method. The Servlet can then store and retrieve session attributes using the HttpSession object.

Q5: How can Servlets be tested?
Ans: We can test Servlets using a web server or a Servlet container such as Tomcat or Jetty. These containers provide a testing environment that simulates HTTP requests and responses. We can also use tools such as JUnit to write unit tests for our Servlets.