Servlet

As internet users, we are aware that on a daily basis, petabytes of data pass through internet servers and are requested by billions of devices worldwide.

The majority of it comes from users who use various devices such as smartphones, tablets, laptops, IoT devices, and so on. In most cases, users are searching the internet for information, which is then rendered as web pages on their devices. These websites are created using programming languages such as PHP, ASP.Net, Javascript, Python, and Java. If we're talking about Java, the services that bring this data are built with Servlets.

We will delve deeply into the concept of Servlet in this post, but first we must understand the web architecture.

The web is a setup of connected servers that serve documents of specific formats though they are hosted differently. The documents or pages shown to end-users are formatted using a markup language called HTML (HyperText Markup Language) that supports links to other documents/pages, like videos, audios, pictures, animations, etc.

Take Facebook as an example: different sections such as Posts, Short Reels, and Stories are all small pages embedded within a larger frame known as a website. On every website, there are two methods for manipulating data. These are the GET and POST commands. The GET method retrieves data from internet servers and displays it on an HTML page, whereas the POST method uploads data to the internet, such as when creating a Facebook post, story, or short reel.

Java Servlets are used to create web applications that generate dynamic web pages rather than static ones. Because it is supported by the Java programming language and runs on a Java-enabled web server or application server, this technology is both robust and scalable. They are used to intercept the request from the web server, process the request, generate the response based on the code block or algorithm, and send the response back to the web server.

In technical terms, a servlet is a Java class used to broaden the capabilities of servers that host applications accessed by means of a request-response programming model. Java Servlets can respond to any type of request and are commonly used to extend the applications hosted by web servers and are defined by HTTP-specific servlet classes.

Two packages are crucial in this regard: javax.servlet and javax.servlet.http. These packages contain interfaces and classes for creating servlets. According to the rule, servlets must implement the Servlet interface, which defines lifecycle methods. In addition, for implementing a generic service, we can use or extend the GenericServlet class provided with the Java Servlet API. The class, HttpServlet, exposes methods such as doGet and doPost to handle HTTP-specific services.

• Loading Servlet:- Loads the servlet class e.g. loading on a web server that is running Apache Tomcat.

• Initializing Servlet:- Initializes the servlet instance by calling the init method

• Handling request:- Invokes the service method, passing request and response objects.

• Destroying Servlet:- If it needs to remove the servlet, the container finalizes the servlet by calling the servlet’s destroy method.

init and destroy methods are called only once. Once out of scope, a servlet is garbage collected by the garbage collector of the Java virtual machine famously known as JVM.

1. Create a Servlet
2. Compile the Servlet
3. Add mappings to the web.xml file
4. Start the server and deploy the project
5. Access the servlet

Let’s expand on the above points.

To run a servlet program, a prerequisite is to have Apache Tomcat Server installed and configured. Do note that for any Servlet program, you will need 3 files – index.html file, Java class file, and web.xml file.

Let’s perform a small exercise in which we will multiply two numbers using Servlets and displays the output in a browser.

The above code creates a form to enter the numbers for the multiplication operation.

And the last step is to add mappings to the web.xml file. The web.xml file will be present in the WEB-INF folder of the web content.

Once the above steps are done, we can execute the program by starting the webserver and getting the desired output on the browser.

• Portability:- It uses Java language which is machine-independent.

• Performance:- It creates a thread for each request, not a process that makes it better.

• Robust:- Java virtual machine manages Servlets, which handles memory leaks, garbage collection, etc.

• Secure:- It uses Java language which is in principle secure.

In this post, we saw how Servlets in Java provide a robust and secure way of displaying and posting data via web pages. To effectively use it by Java developers, one must excel at understanding the underlying concepts and implement pet projects to gain a thorough understanding of Servlet so that he can use it in client-specific projects.