JAVA EE: WebServlet Annotation

Showing posts with label WebServlet Annotation. Show all posts

Friday, 6 June 2014

Servlet with Annotation

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The Evolution of Servlet Configuration

Traditionally, configuring Java servlets required declaring every servlet mapping and initialization parameter in the XML-based deployment descriptor (web.xml). While this approach centralized application configuration, large enterprise applications often resulted in verbose, difficult-to-maintain XML files.

Starting with Servlet 3.0, Java EE introduced annotations to streamline web component registration directly within Java source code. By leveraging annotations such as @WebServlet, developers can declare URL mappings, initialization parameters, and startup behavior directly on the class definition, eliminating the need for bulky XML declarations.

Configuring Servlets with @WebServlet

The @WebServlet annotation (from the javax.servlet.annotation package) provides a clean, declarative syntax. It supports a variety of attributes that mirror traditional web.xml tags:

urlPatterns (or value): Specifies the URL path or patterns that trigger the servlet.
name: Defines the logical name of the servlet component.
loadOnStartup: Controls whether the container initializes the servlet eagerly at application deployment or lazily on first request.
initParams: Allows defining key-value initialization parameters using nested @WebInitParam annotations.

@WebServlet(

        name = "UserServlet",

        urlPatterns = {"/users", "/profile"},

        loadOnStartup = 1,

        initParams = {

            @WebInitParam(name = "defaultRole", value = "Guest")

        }

    )

    public class UserServlet extends HttpServlet {

        @Override

        protected void doGet(HttpServletRequest req, HttpServletResponse resp) 

                throws ServletException, IOException {

            resp.getWriter().println("Servlet configured cleanly with annotations!");

        }

    }

Key Advantages of Annotation-Based Servlets

Reduced Boilerplate: No need to write duplicate servlet declarations and servlet-mapping blocks in web.xml.
High Cohesion: Configuration settings live right alongside the servlet's implementation code, making refactoring and maintenance straightforward.
Flexible Override: Deployment descriptors can still override annotations when environment-specific customization is needed.

Recommended Related Tutorials

Continue exploring servlet fundamentals and architecture with these tutorials from Ram N Java:

Click here to watch in Youtube : https://www.youtube.com/watch?v=9BkjzpuJK4w

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Servlet with Annotation

AnnotationServletDemo Project Dir Structure

Servlet with Annotation

HelloServlet.java

import java.io.IOException;
import java.io.PrintWriter;

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("/hello")
public class HelloServlet extends HttpServlet
{
    private static final long serialVersionUID = 1L;

    public void init() throws ServletException
    {
        System.out.println("-----------------------------------------");
        System.out.println(" Init method is called in "
                + this.getClass().getName());
        System.out.println("--------------------------------------");
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException
    {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        out.print("<html><body>");
        out.print("<h3>Hello Servlet</h3>");
        out.print("</body></html>");

    }

    public void destroy()
    {
        System.out.println("-----------------------------------------");
        System.out.println(" destroy method is called in "
                + this.getClass().getName());
        System.out.println("-----------------------------------------");
    }

}

index.html

<html lang="en">
<head>
<meta charset="UTF-8">
<title>ServletContextAttributeDemo</title>
</head>
<body>
    <form action="hello" method="GET">
        <input type="submit" value="Submit" />
    </form>
</body>
</html>

Environment Used

JDK version :1.7.0_51
Tomcat version : 7.0.50

To Download AnnotationServletDemoApp Project Click the below link

https://sites.google.com/site/javaee4321/servlets/AnnotationServletDemoApp.zip?attredirects=0&d=1

See also:

Servlets Tutorial

All Design Patterns Links