Difference Between Java Servlet and CGI

Last Updated : 6 Jan 2026

In the realm of web development, Java Servlet and CGI (Common Gateway Interface) are two different technologies that serve a common purpose: handling dynamic content on the web. However, Java Servlets and CGI have distinct characteristics, and understanding their differences is crucial for developers.

Java Servlet

Java Servlet is a Java-based programs that extend the functionality of a web server to generate dynamic content. Servlets are managed by the Java Servlet Container, a part of the web server or a separate application server. The servlet container communicates with the servlet through the Java Servlet API.

To read more Java Servlet

Here's a simple example of a Java Servlet:

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/HelloServlet")
public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.getWriter().println("<html><body><h2>Hello, Java Servlet!</h2></body></html>");
    }
}

Explanation:

The HelloServlet class extends HttpServlet and is annotated with @WebServlet to define its URL mapping.

The doGet() method is invoked when a client sends an HTTP GET request to the servlet. In this example, it sets the content type to HTML and sends a simple greeting message.

Common Gateway Interface (CGI)

CGI is a standard protocol that allows web servers to execute external programs or scripts to generate dynamic content. CGI scripts can be written in various programming languages, such as Perl, Python, or even shell scripts. Unlike Java Servlets, CGI is language-agnostic.

Here's a basic example of a CGI script written in Perl:

#!/usr/bin/perl
use strict;
use warnings;
print "Content-type: text/html\n\n";
print "<html><body><h2>Hello, CGI!</h2></body></html>";

Explanation

The shebang (#!/usr/bin/perl) indicates that this script should be executed using the Perl interpreter.

The Content-type header is crucial in CGI to specify the type of content being returned (in this case, HTML).

Comparison

Performance

Servlets are generally faster than CGI scripts. Servlet containers maintain a pool of servlet instances, eliminating the need to create a new process for each request.
CGI scripts create a new process for every request, resulting in higher overhead.

Language Dependency

Servlets are Java-specific, requiring developers to use the Java programming language.
CGI is language-agnostic, allowing developers to use different languages for scripting.

Resource Usage

Servlets consume less system resources compared to CGI scripts due to the servlet container's efficient management.
CGI scripts may lead to higher resource usage as each script execution involves launching a new process.

Java Servlets Vs. CGI

Feature	CGI	Java Servlets
Definition	CGI is a method where web servers run external scripts or programs to generate dynamic web pages.	A Java Servlet is a Java program that runs inside a web server to handle requests and generate dynamic content.
Execution	For every user request, the server creates a new process. This adds overhead and slows things down.	A single servlet is loaded once, and every request is handled in a lightweight thread, making it much faster.
Performance	Slower, especially when handling multiple requests at once, due to multiple processes being created.	Much better performance because it uses threads, not separate processes.
Resource Usage	It uses a lot more memory and CPU as each request launches a new process.	More efficient requests are handled using the same servlet instance with different threads.
Programming Language	CGI scripts can be written in many languages Perl, Python, C, Bash, etc.	Servlets are written only in Java.
Platform Independence	Depends on the language used and the OS it runs on.	Platform-independent because Java runs on the Java Virtual Machine (JVM).
Ease of Maintenance	Can get messy as large applications may have scripts in multiple languages.	Easier to manage and maintain due to Java's object-oriented features and structure.
Scalability	Not ideal for large-scale applications. More users = more processes = more server load.	Great for scalable applications. Handles thousands of users efficiently using multithreading.
Code Reusability	Limited. CGI scripts are often standalone and not reusable.	High servlets are part of a larger Java class structure and can be reused and extended easily.
Resource Usage	It can lead to higher resource usage as each script execution involves launching a new process.	More efficient due to servlet container's management of instances.
State Management	Stateless by default; state management needs to be handled explicitly.	Built-in support for session management and state persistence.
Concurrency	Limited concurrency due to the creation of a new process for each request.	Supports multithreading and efficient resource utilization.
Common Use Cases	Lightweight scripts, simple web applications, or when language flexibility is required.	Enterprise-level web applications, dynamic content generation.

Conclusion

Understanding the differences between Java Servlets and CGI is essential for choosing the right technology for web development projects. While Servlets offer better performance and resource efficiency, CGI provides language flexibility. Developers should consider project requirements, performance expectations, and language preferences when deciding between these two technologies.

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