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Table of contents
1.
Introduction
2.
What is a Java Servlet?
3.
 Properties of a java servlet
4.
Java Servlet Architecture
5.
Java Servlet Features
6.
Why do we need a java servlet?
7.
What is CGI?
8.
Difference between CGI and  Java Servlets
9.
Servlets APIs
9.1.
1. javax.servlet
9.2.
2. javax.servlet.http
10.
Advantages of  Java Servlet
11.
Disadvantages of Java Servlet
12.
The Servlet Container
13.
Frequently Asked Questions
13.1.
Is servlet an MVC?
13.2.
Is servlet a class or interface?
13.3.
Why servlet is faster than JSP?
13.4.
Is servlet thread safe?
13.5.
What are types of servlet in Java?
14.
Conclusion
Last Updated: Jun 13, 2024
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What is Servlet in Java?

Author Amit Singh
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Introduction

Servlets are a fundamental component of Java web development, serving as the backbone for dynamic web applications. In the realm of Java Enterprise Edition (Java EE), now Jakarta EE, servlets provide the foundation for handling client requests, processing data, and generating dynamic responses on the server-side. In this article, we will understand what is a servlet in Java and how they function.

servlet in java

We will also learn the architecture of a servlet with advantages and disadvantages. Then we will focus on CGI. Finally, we will differentiate between Servlet and CGI. Let's dive into the article to learn more about the topic.

What is a Java Servlet?

A servlet is a class of Java programming language. You can use it to increase the functionality of servers that host applications based on the programming model, i.e., request-response. Servlets can react to any request, but they are frequently used to expand the functionality of web server-hosted applications. Java Servlet technology creates HTTP-specific servlet classes for these applications.

There are classes and interfaces for writing servlets in the javax.servlet and javax.servlet.http packages. The Servlet Lifecycle methods are defined by the Servlet interface, which all servlets must implement. You can take the help of Java Servlet API to extend the GenericServlet class for developing a generic service. For dealing with services related to HTTP, the HttpServlet class offers methods like doGet and doPost.

After “what is servlet”, let’s move on to the properties of servlets.

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 Properties of a java servlet

Servlets have the following properties:-

  • The interface of the Servlet defines the life cycle methods of a servlet. It includes init()service(), and destroy().
     
  • Servlets are executed within the Java Virtual Machine (JVM) of the web server. This allows for more efficient use of resources. It also leads to better scalability.
     
  • Servlets are platform-independent. It is so because they are written in Java. So, it can run on any platform that supports a JVM.
     
  • Servlets have built-in support for session management. 
     
  • You can use Servlets to handle different types of requests. These requests can be GET, POST, PUT, DELETE, etc.
     
  • You can set up Servlets using either annotations or a web.xml file.
     
  • You can use Servlets to take care of requests made by a user and create a proper response to send back to the user.
     
  • You can use Servlets to handle errors that may occur during the request execution.
     

Java Servlet Architecture

Let's try to understand the architecture of the servlet.

servlet architecture

Step 1: Initially, the client will send the request to the server using the browser.
 

Step 2: The server will accept the request and send it to the required servlet container. Servlet container has other names like servlet engine or web container. It handles the life cycle of the servlet.
 

Step 3: Servlet container tries to understand the URL of the request and makes a call to the specific container. After the call, it starts a thread to run the servlet. If the same servlet receives several requests, only one thread will be started for each request.
 

Step 4: After communicating with the database or carrying out any other actions, the servlet processes the request object, prepares the response object, and then delivers the response object back to the web server.
 

Step 5: Finally, the server will send back the response to the client or the browser.

Java Servlet Features

Java Servlets, as a crucial part of Java web development, offer a range of features that empower developers to create dynamic, scalable, and efficient web applications. Here are some key features of Java Servlets:

  • Platform Independence: Servlets are written in Java, which means they are platform-independent and can run on any platform that supports the Java Virtual Machine (JVM).
  • Server-side Processing: Servlets execute on the server-side, allowing developers to handle client requests, process data, and generate dynamic responses before sending them back to the client.
  • HTTP Protocol Support: Servlets are specifically designed to work with the Hypertext Transfer Protocol (HTTP), making them ideal for building web applications that communicate over the internet.
  • Lifecycle Management: Servlets have a well-defined lifecycle consisting of initialization, service, and destruction phases. Developers can override lifecycle methods to perform tasks such as initialization, request processing, and resource cleanup.
  • Multithreading: Servlet containers manage the lifecycle of servlet instances and handle multithreading automatically. Each request to a servlet is typically processed in a separate thread, allowing servlets to handle multiple requests concurrently.
  • Session Management: Servlets support session management, enabling developers to maintain stateful interactions with clients across multiple requests. Servlet containers provide session tracking mechanisms, such as cookies or URL rewriting, to associate requests with specific sessions.

Why do we need a java servlet?

Servlets are needed for building web applications. We need servlets because of the following reasons:-

  • Servlets are faster and more efficient than older technologies like CGI.
     
  • Servlets are portable and can run on platforms that support Java.
     
  • Servlets provide built-in support for session management.
     
  • Servlets can handle multiple requests and helps in improving memory utilization.
     
  • Servlets are easy to develop and maintain.
     
  • Servlets have more control over the request-response cycle.
     
  • Servlets have an exception-handling mechanism.

What is CGI?

CGI stands for Common Gateway Interface. It is an external application written in programming languages like C or C++. You can use it for handling client requests and generating dynamic content. When a client requests dynamic web pages, the web server performs the following steps:

  • It identifies the requested web page using the URL. This is the required CGI application.
     
  • It creates a new process to handle the client's request.
     
  • The CGI application is invoked within the process, and the request information is passed.
     
  • The response from the CGI application is collected.
     
  • Finally, the process is destroyed. The HTTP response is prepared and sent back to the client.
     

This approach of CGI is only suitable for handling a small number of clients. As the number of clients increases, the workload on the server increases. Thus the time required to process requests also increases. Creating and destroying a process for every request can be resource-intensive. This makes CGI less efficient as compared to other technologies such as Servlets and JSPs.

CGI gateway

Difference between CGI and  Java Servlets

CGI (Common Gateway Interface) and Servlet are technologies for handling web requests. But they have some key differences. We have mentioned these differences below:-

S.No.

CGI

Servlet

1.

It is less portable than servlets.It is more portable than CGI.

2.

It executes a new process for each request, so it is less efficient.It executes within a single JVM so it is more efficient.

3.

CGI scripts do not have built-in support for session management. This means it has to be implemented in the script manually.Servlets provide built-in support for session management. This makes it easier to maintain track of the user's session.

4.

It is an older technology and is less scalable than servlets.It is more scalable than servlets.

5.

It is limited to specific languages and can run on certain platforms only .It is written in Java and  can run on any platform that supports Java.

6.

It runs as a separate program outside of the web server.It runs inside the web server.

Servlets APIs

Just like any other API(Application Programming Interface), Servlet API allow to interact with the servlet container through requests and response.

It comes in two packages, which are:

  1. javax.servlet
  2. javax.servlet.http

 

Let’s see each of the packages in detail.

1. javax.servlet

It consists of classes and interfaces describing the contracts connecting the servlet class and the runtime environment allocated for a class instance.

2. javax.servlet.http

It consists of classes and interfaces responsible for http requests only. 

Some of the classes in javax.servlet.http include:

  • HttpServlet
  • HttpSessionBindingEvent
  • HttpServletRequestWrapper
  • HttpSessionEvent
  • HttpServletResponseWrapper
  • Cookie
  • HttpUtils (deprecated now)

 

Some of the interfaces present in javax.servlet.http include:

  • HttpServletRequest
  • HttpSessionListener
  • HttpServletResponse
  • HttpSessionAttributeListener
  • HttpSession
  • HttpSessionActivationListener
  • HttpSessionBindingListener
  • HttpSessionContext (deprecated now)

Advantages of  Java Servlet

Some of the advantages of servlet are as follows:

  • Its provides better performance as it creates a new thread for each request and not process
     
  • It is portable as it is based on java
     
  • It has highly secure as it uses java
     
  • It is server-independent and is compatible with all the web servers available currently
     
  • It is persistent and remains in memory until we destroy it
     
  • It is faster

Disadvantages of Java Servlet

Some of the disadvantages of servlet are:

  • It is complex to understand and maintain
     
  • It has limited built-in support compared to other web development technologies
     
  • Designing is complex, which can make the application slow
     
  • These are not highly scalable and have slower performance

The Servlet Container

Servlet container in Java interacts with the web server and generates dynamic web pages.

So, if you do not want to access static web pages and instead you are looking for web pages based on the user input, then you can use a servlet container. 

The servlet container performs several operations, like:

  • Multithreaded support
     
  • Life Cycle Management
     
  • Security 
     
  • Object Pooling

Frequently Asked Questions

Is servlet an MVC?

MVC stands for Model View and Controller. The original Servlet API-based web framework, Spring Web MVC, has been a part of the Spring Framework since its inception.
In the context of Java, the model contains simple java classes, controller consists of servlets, and view contains the JSP pages.

Is servlet a class or interface?

A servlet is a class of java programming language used to extend the capabilities of servers that host applications accessed via a request-response programming model. Servlets can respond to any request type.  But they are commonly used to extend the applications hosted by web servers.

Why servlet is faster than JSP?

JSP is slower than Servlets because of its longer response times. JSP is slower than Servlets because the first step in the JSP lifecycle is to translate JSP into Java code, which is subsequently compiled. Servlets use java-based code. JSP is an HTML-based language.

Is servlet thread safe?

Yes, Servlet is thread-safe by default. The Servlet container ensures that each request is processed in a separate thread, and that thread-safety is maintained by synchronizing access to shared resources such as servlet objects or session attributes.

What are types of servlet in Java?

There are two types of servlets in Java: generic servlets and HTTP servlets. Generic servlets are protocol-independent and can handle any type of request, while HTTP servlets are specific to the HTTP protocol and are used to handle HTTP requests and responses.

Conclusion

In this article, we have discussed what is servlet in Java. Servlet plays a pivotal role in Java web development, offering developers a robust framework for building dynamic and interactive web applications. 

Check out some articles on Servlet like spring boot auto configuration and dispatcher servlet and top spring mvc interview questions.

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