Servlet Program in Java

Last Updated on June 12, 2024 by Abhishek Sharma

Servlets are a fundamental component of Java EE (Enterprise Edition) used to create dynamic web applications. A servlet is a Java programming class that is used to extend the capabilities of servers hosting applications accessed via a request-response programming model. They run on a server, typically a web server or an application server, and handle requests from web clients, such as browsers, process these requests, and generate dynamic responses.

Servlets provide a powerful mechanism for developing server-side applications, offering a robust and scalable environment for handling HTTP requests and responses. Unlike traditional CGI (Common Gateway Interface) scripts, servlets are managed by the Java Virtual Machine (JVM), which provides advantages like platform independence, improved performance, and enhanced security.

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
Servlet programming is a cornerstone of Java-based web development, providing a robust and scalable framework for creating dynamic web applications. Servlets enable efficient request processing, dynamic content generation, and seamless integration with other Java EE components. By understanding the basics of servlets, including their lifecycle, configuration, and common operations, developers can build powerful web applications that leverage the full potential of the Java ecosystem.

FAQs on Servlet Program in Java

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

1. What is a servlet in Java?
A servlet is a Java class used to handle requests and generate responses in a web server environment. It extends the capabilities of servers by providing a way to create dynamic web content and interact with web clients through a request-response model.

2. How does a servlet work?
A servlet works by following these steps:

• Initialization: The servlet is initialized by the server.
• Request Handling: The server forwards client requests to the servlet.
• Processing: The servlet processes the request, interacts with databases or other resources if needed, and generates a response.
• Response: The servlet sends the response back to the client.
• Termination: The servlet is terminated by the server when it’s no longer needed.

3. What are the advantages of using servlets over traditional CGI?
Advantages of using servlets over traditional CGI include:

• Performance: Servlets are faster as they use multithreading, whereas CGI creates a new process for each request.
• Portability: Servlets are platform-independent and can run on any server that supports the Java Servlet API.
• Scalability: Servlets can handle large numbers of requests efficiently.
• Integration: Servlets can easily interact with other Java components and APIs.

4. What is the lifecycle of a servlet?
The lifecycle of a servlet consists of:

• Loading and Instantiation:**** The servlet class is loaded and an instance is created.
• Initialization (init method): The servlet is initialized by calling the init method once.
• Request Handling (service method): The service method is called for each client request, delegating to doGet, doPost, etc.
• Destruction (destroy method): The servlet is destroyed by calling the destroy method once, freeing up resources.

5. What is the difference between doGet and doPost methods?
The doGet method handles HTTP GET requests, typically used for retrieving data. The doPost method handles HTTP POST requests, typically used for sending data to the server for processing. doPost is often used for form submissions where sensitive or large amounts of data are sent.