@WebServlet Annotation Example (Jakarta EE)

Author:
In this blog post, we'll explore the usage of the @WebServlet annotation from the jakarta.servlet package to create and configure servlets in Java. The @WebServlet annotation simplifies the process of servlet declaration and configuration, eliminating the need for web.xml entries. We will demonstrate a complete example using the latest Jakarta Servlet dependency.

Step 1: Add Servlet Dependency to pom.xml

First, we need to add the Jakarta Servlet dependency to our pom.xml file. Here, we are using version 6.1.0.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>net.javaguides.servlet.tutorial</groupId>
    <artifactId>java-servlet-tutorial</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>java-servlet-tutorial Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <!-- Jakarta Servlet dependency -->
        <dependency>
            <groupId>jakarta.servlet</groupId>
            <artifactId>jakarta.servlet-api</artifactId>
            <version>6.1.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>java-servlet-tutorial</finalName>
    </build>
</project>

Step 2: Create a Servlet Using @WebServlet Annotation

Now, let's create a simple servlet using the @WebServlet annotation.

HelloWorldExample.java

package net.javaguides.servlet.tutorial.httpservlet;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

@WebServlet(urlPatterns = "/helloworld")
public class HelloWorldExample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter printWriter = resp.getWriter();
        printWriter.print("<html>");
        printWriter.print("<body>");
        printWriter.print("<h1>Hello World HttpServlet Class Example</h1>");
        printWriter.print("<a href=\"http://www.javaguides.net\">Java Guides</a>");
        printWriter.print("</body>");
        printWriter.print("</html>");
        printWriter.close();
    }
}

In this example, the servlet HelloWorldExample is mapped to the URL pattern /helloworld. When accessed, it displays a simple HTML page.

Commonly Used @WebServlet Annotation Attributes

The @WebServlet annotation comes with several attributes that allow for fine-grained configuration of servlets. Here are some commonly used attributes:

  • urlPatterns or value: Defines the URL patterns to which the servlet responds.
  • name: Provides a name for the servlet.
  • description: Adds a description to the servlet.
  • initParams: Specifies initialization parameters for the servlet.
  • loadOnStartup: Determines the load order of the servlet.
  • asyncSupported: Indicates whether the servlet supports asynchronous processing.

For a complete list of attributes, refer to the official Jakarta Servlet API documentation.

Additional @WebServlet Annotation Examples

Multiple URL Patterns

A servlet can be mapped to multiple URL patterns.

import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;

@WebServlet(urlPatterns = {"/helloworld", "/greeting"})
public class SampleUsingAnnotationAttributes extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Handle the request
    }
}

Naming the Servlet

The name attribute can be used to give the servlet an explicit name.

@WebServlet(name = "MyServlet", urlPatterns = {"/foo", "/bar"})
public class SampleUsingAnnotationAttributes extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Handle the request
    }
}

Adding a Description

The description attribute can be used to describe the servlet.

import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;

@WebServlet(
        name = "MyOwnServlet",
        description = "Describe Servlet",
        urlPatterns = "/helloworld"
)
public class HelloWorldServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Handle the request
    }
}

Init Parameters

Init parameters can be defined using the initParams attribute.

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebInitParam;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

@WebServlet(
    urlPatterns = "/userinfo",
    initParams = {
        @WebInitParam(name = "firstName", value = "Ramesh"),
        @WebInitParam(name = "lastName", value = "Fadatare")
    }
)
public class HttpServletExample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String firstName = getInitParameter("firstName");
        String lastName = getInitParameter("lastName");

        PrintWriter writer = resp.getWriter();

        writer.println("firstName = " + firstName);
        writer.println("lastName = " + lastName);
    }
}

Asynchronous Operation and Load-on-Startup

You can configure the servlet for asynchronous operation and specify the load-on-startup order.

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

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

@WebServlet(
    urlPatterns = "/helloworld",
    loadOnStartup = 1,
    asyncSupported = true
)
public class HttpServletExample extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.setContentType("text/html");
        PrintWriter printWriter = resp.getWriter();
        printWriter.print("<html>");
        printWriter.print("<body>");
        printWriter.print("<h1>Hello World HttpServlet Class Example</h1>");
        printWriter.print("<a href=\"http://www.javaguides.net\">Java Guides</a>");
        printWriter.print("</body>");
        printWriter.print("</html>");
        printWriter.close();
    }
}

Conclusion

In this blog post, we demonstrated the usage of the @WebServlet annotation to create and configure servlets in Java. We covered various attributes of the @WebServlet annotation, including urlPatterns, name, description, initParams, loadOnStartup, and asyncSupported. Using annotations simplifies servlet development by eliminating the need for web.xml configuration.

References

Related Servlet Posts

Comments

Post a Comment

Leave Comment