Introduction to Servlets

Embark on your journey into the world of servlets with Innostax's comprehensive guide. Start mastering servlets today with Innostax.

Sahil Khurana

Published: February 7, 2024

Key takeaways

Servlets control dynamic WEB content based on expansion of server functions and handling of convened requests with the clearly defined life cycle providing for correct utilization of the necessary resources after the start of the program, request handling, and program termination.
Servlets have high efficiency because they are compiled into byte code; besides, servlets can be scaled vertically using application servers and load balancing features and horizontally using clustering.
Java Servlets work well with other Java EE technologies and frameworks including JSP, JSF, and EJB and Propositions with other Java Servlets which makes it an ideal platform for server-side scripting and building of robust, secure web applications.

Servlets are Java classes used to extend the capabilities of servers. servlets handle requests and generate responses, making them essential for dynamic web applications. They have a well-defined life cycle, which starts when it is loaded into the memory and ends when it is removed. They are used in big and old projects like for most banking software development companies and java software development services uses Servlets for its Scalability and easy integration.

Servlet Life Cycle:

It is a group of steps that a servlet goes through from its creation to its destruction. There are four Stages in its LifeCycle.

The life cycle followed a path from its creation to destruction:

It is borned
It is initialized
It is ready to service
It is servicing
It is not ready to service
It is destroyed

Loading

When the web application starts the servlet container loads the servlet class into the memory.

Initialization

The container creates an instance of the servlet and initializes it by calling its init() method. This method is called only once during the life cycle and is used for initialization tasks such as opening a database connection or reading configuration parameters.

public class MyServlet implements Servlet {
   @Override
   public void init(ServletConfig config) throws ServletException {
      
   }

public class MyServlet implements Servlet {

@Override

public void init(ServletConfig config) throws ServletException {

}

Request Processing

The servlet container calls the service() method of the servlet to process client requests.

This method calls when we receive a request from the client.

public class MyServlet implements Servlet {

   @Override
   public ServletConfig getServletConfig() {
       return null;
   }

   @Override
   public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

   }

public class MyServlet implements Servlet {

@Override

public ServletConfig getServletConfig() {

return null;

}

@Override

public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

}

In this getServletConfig() is an interface of Servlet that initializes the Servlet.

Servlet returns a ServletConfig object, which contains initialization and startup parameters for the servlet.

The service method is responsible for handling incoming HTTP requests. It dispatches requests to the appropriate HTTP methods (doGet, doPost, doPut, doDelete, etc.) based on the request type.

Implementations of its interface are responsible for storing the ServletConfig object so that this method can return it. The GenericServlet class, which implements this interface, already does this.

Destruction

The servlet calls the destroy() method of the servlet when the web application is stopped or when the servlet is removed from the container. This method is used for cleanup tasks such as closing the database connection and releasing system resources.

public class MyServlet implements Servlet {

   @Override
   public ServletConfig getServletConfig() {
       return null;
   }

   @Override
   public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

   }

   @Override
   public void init(ServletConfig config) throws ServletException {

   }

   @Override
   public String getServletInfo() {
       return null;
   }

   @Override
   public void destroy() {

   }

public class MyServlet implements Servlet {

@Override

public ServletConfig getServletConfig() {

return null;

}

@Override

public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

}

@Override

public void init(ServletConfig config) throws ServletException {

}

@Override

public String getServletInfo() {

return null;

}

@Override

public void destroy() {

}

getServletInfo in the interface of Servlet it returns a String that contains information related to the servlet and its methods.

The getServletInfo interface returns information about the servlet, such as author, version, and copyright.

The getServletInfo method returns a string that would be of plain text and not markup of any kind (such as HTML, XML, etc.)

Types of Servlets:

GenericServlet

GenericServlet is a generic abstract class in Java, which is used to develop server objects that adhere to protocol standards and support different protocols. It is designed an abstract class that is to be implemented coder-specific like HTTP servlets.

The method offers to manage lifecycle to include initialization (initialize()) and elimination (destroy()). With subclasses you can override these methods to perform a task of initialization when the servlet is loaded in the memory and a cleanup task when it is unload.

GenericServlet allows you to perform actions like getting configuration parameters from the settings that are specified in the deployment descriptor (Web.xml). Subclasses can use such method to get init arguments and also other settings that are application-oriented.

 import javax.servlet.GenericServlet;
       import javax.servlet.ServletException;
       import javax.servlet.ServletRequest;
       import javax.servlet.ServletResponse;
       import java.io.IOException;

       public class MyServlet extends GenericServlet {

      @Override
      public void service(ServletRequest req, ServletResponse res) 
      throws ServletException, IOException {

import javax.servlet.GenericServlet;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import java.io.IOException;

public class MyServlet extends GenericServlet {

@Override

public void service(ServletRequest req, ServletResponse res)

throws ServletException, IOException {

HttpServlet

HttpServlet is a subclass of GenericServlet that provides additional methods for handling HTTP requests. It implements the HttpServletRequest and HttpServletResponse interfaces, which provide methods for accessing HTTP request and response headers, parameters, and other information.

HttpServlet provides by default implementations for the method doGet(), doPost(), doPut(), doDelete(), and other HTTP request methods.

package com.siena.web;

import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import java.io.IOException;

public class MyServlet extends HttpServlet {
 @Override
   public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

   }
}

package com.siena.web;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServlet;

import java.io.IOException;

public class MyServlet extends HttpServlet {

@Override

public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

}

Some Methods of Http ServletClass:

doGet : If the servlet supports HTTP GET requests

public class MyServlet extends HttpServlet {

    // The doGet() method handles HTTP GET requests
public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response content type
        response.setContentType("text/html");

        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;Hello World from doGet() method!&lt;/h1&gt;");
    }

public class MyServlet extends HttpServlet {

// The doGet() method handles HTTP GET requests

public void doGet(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Set response content type

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>Hello World from doGet() method!</h1>");

}

doPost : For HTTP POST requests

// The doPost() method handles HTTP POST requests
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response content type
        response.setContentType("text/html");

        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;Hello World from doPost() method!&lt;/h1&gt;");
    }

// The doPost() method handles HTTP POST requests

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Set response content type

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>Hello World from doPost() method!</h1>");

}

doPut : For HTTP PUT requests

The doPut() method handles HTTP PUT requests
    public void doPut(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response status code and content type
        response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
        response.setContentType("text/html");

        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;HTTP PUT method is not supported!&lt;/h1&gt;");
    }

The doPut() method handles HTTP PUT requests

public void doPut(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Set response status code and content type

response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>HTTP PUT method is not supported!</h1>");

}

doDelete : For HTTP DELETE requests init & destroy : To manage resources that are held for the life of the servlet

// The doDelete() method handles HTTP DELETE requests
    public void doDelete(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response status code and content type
        response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
        response.setContentType("text/html");
        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;HTTP DELETE method is not supported!&lt;/h1&gt;");
    }

// The doDelete() method handles HTTP DELETE requests

public void doDelete(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Set response status code and content type

response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>HTTP DELETE method is not supported!</h1>");

}

getServletInfo : Used to provide information about itself

doHead : It receives an HTTP HEAD request from the protected service method and handles the request

doOptions : Called by the server to handle a OPTIONS request.

 // The doOptions() method handles HTTP OPTIONS requests
    public void doOptions(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Set response status code and content type
        response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
   response.setContentType("text/html");

        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;HTTP OPTIONS method is not supported!&lt;/h1&gt;");
    }

// The doOptions() method handles HTTP OPTIONS requests

public void doOptions(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Set response status code and content type

response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>HTTP OPTIONS method is not supported!</h1>");

}

doTrace : Called by the server to handle a TRACE request.

// The doTrace() method handles HTTP TRACE requests
    public void doTrace(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // Robust and Efficient: response status code and content type
        response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);
        response.setContentType("text/html");

        // Actual logic goes here
        PrintWriter out = response.getWriter();
        out.println("&lt;h1&gt;HTTP TRACE method is not supported!&lt;/h1&gt;");
    }

// The doTrace() method handles HTTP TRACE requests

public void doTrace(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

// Robust and Efficient: response status code and content type

response.setStatus(HttpServletResponse.SC_METHOD_NOT_ALLOWED);

response.setContentType("text/html");

// Actual logic goes here

PrintWriter out = response.getWriter();

out.println("<h1>HTTP TRACE method is not supported!</h1>");

}

getLastModified : Returns the time the HttpServletRequestobject was last modified, in milliseconds.

Advantages of a Java Servlet:

Platform Independence

They are Java servlets that are installed on a web server so that they can produce dynamic web content and process and handle clients’ requests. They follow the Java Servlet API which functions as a standard interface and undertakes the web development tasks.

Robust and Efficient:

java’s brilliant type system, the ability to handle exceptions as well as memory management are among other things, that make their robustness and efficiency even higher. Because of this, they are more rarely executing memory leaks and security threats which are not native to the technology.

Performance

They are compiled into bytecode, which can be executed more efficiently than interpreted scripts. They are well-suited for high-performance applications.

Server-Side Processing

They permit on-server processing; hence, you can undertake some tasks which may be form handling, database access and session management on the server based on the type of web application as these are important for secure and scalable web applications.

Scalability

Servlet-based Apps can be scaled both vertically and horizontally by virtue of their capability to maintain load normalcy as well as sustain expandable demands.

Speaking of the vertical scalability, it is the process of building up the server capacity by adding prepared resources, e.g. more CPU, memory, or storage.

Horizontal scalability, which distributes load across many servers and is mostly accomplished through load balancing, is a methodology.

Apache Tomcat together with servlet containers and application servers such as, Jetty, etc. have “clustering and load balancing” capabilities to achieve “horizontal scalability.”

Integration

The comprehensive integration with Java EE (Enterprise Edition) technologies and combine with frameworks of various kinds that may be JSP (JavaServer Pages), JSF (JavaServer Faces), EJB (Enterprise Java Beans), and others

They can also, handle with third-party libraries and framework for particular needs such as the security, authentication, authorization, and data access.

Conclusion

Java Servlets are essential for building dynamic web applications, offering robust, efficient, and scalable server-side processing. Their lifecycle—comprising loading, initialization, servicing requests, and destruction—ensures resource optimization. Servlets are widely used in enterprise applications like banking due to their stability and performance.

With GenericServlet for protocol-agnostic tasks and HttpServlet for HTTP-specific handling, Servlets provide flexibility and simplicity for managing web requests. They integrate seamlessly with Java EE technologies and frameworks, ensuring compatibility with diverse ecosystems. Their scalability, platform independence, and strong security features make Servlets a reliable choice for secure, high-performance, and scalable web applications in modern development.

Get a Fast Estimate on Your Software
Development Project

Servlet Life Cycle:
The life cycle followed a path from its creation to destruction:
Loading
Initialization
Request Processing
Destruction
Types of Servlets:
GenericServlet
HttpServlet
Some Methods of Http ServletClass:
Advantages of a Java Servlet:
Platform Independence
Robust and Efficient:
Performance
Server-Side Processing
Scalability
Integration
Conclusion

See how efficient your engineering team really is?

Calculate For Free

Introduction to Servlets

Key takeaways

Servlets control dynamic WEB content based on expansion of server functions and handling of convened requests with the clearly defined life cycle providing for correct utilization of the necessary resources after the start of the program, request handling, and program termination.

Servlets have high efficiency because they are compiled into byte code; besides, servlets can be scaled vertically using application servers and load balancing features and horizontally using clustering.

Java Servlets work well with other Java EE technologies and frameworks including JSP, JSF, and EJB and Propositions with other Java Servlets which makes it an ideal platform for server-side scripting and building of robust, secure web applications.

Servlet Life Cycle:

The life cycle followed a path from its creation to destruction:

Loading

Initialization

Request Processing

Destruction

Types of Servlets:

GenericServlet

HttpServlet

Some Methods of Http ServletClass:

Advantages of a Java Servlet:

Platform Independence

Robust and Efficient:

Performance

Server-Side Processing

Scalability

Integration

Conclusion

Get a Fast Estimate on Your Software
Development Project

Table of Contents

See how efficient your engineering team really is?

Related Blog Articles

Introduction to Servlets

Key takeaways

Servlets control dynamic WEB content based on expansion of server functions and handling of convened requests with the clearly defined life cycle providing for correct utilization of the necessary resources after the start of the program, request handling, and program termination.

Servlets have high efficiency because they are compiled into byte code; besides, servlets can be scaled vertically using application servers and load balancing features and horizontally using clustering.

Java Servlets work well with other Java EE technologies and frameworks including JSP, JSF, and EJB and Propositions with other Java Servlets which makes it an ideal platform for server-side scripting and building of robust, secure web applications.

Servlet Life Cycle:

The life cycle followed a path from its creation to destruction:

Loading

Initialization

Request Processing

Destruction

Types of Servlets:

GenericServlet

HttpServlet

Some Methods of Http ServletClass:

Advantages of a Java Servlet:

Platform Independence

Robust and Efficient:

Performance

Server-Side Processing

Scalability

Integration

Conclusion

Get a Fast Estimate on Your Software Development Project

Table of Contents

See how efficient your engineering team really is?

Related Blog Articles

Get a Fast Estimate on Your Software
Development Project