Java Language - 93 - Servlets

Java Enterprise Edition (Java EE) – Servlets

Introduction to Java EE and Servlets

Java Enterprise Edition (Java EE) is a set of specifications that extends the Java Platform, Standard Edition (Java SE) to provide comprehensive enterprise application development features. Among the key components of Java EE, Servlets play a critical role in web application development. Servlets are Java classes that extend the capabilities of servers to respond to client requests.

Key Concepts and Features

Java EE Servlets come with a range of features that make them essential for building dynamic web applications:

Server-Side Processing: Servlets are server-side components that process client requests on the web server, allowing you to generate dynamic web content.
Platform Independence: Servlets are written in Java, which ensures platform independence and portability.
Request and Response Handling: Servlets handle incoming HTTP requests and generate HTTP responses, making them ideal for web application development.
Lifecycle: Servlets have a well-defined lifecycle with methods like init(), service(), and destroy(), enabling developers to manage resources and request handling.

Servlet Example

Let’s take a look at a simple example of a Java EE Servlet. In this example, we’ll create a basic “HelloServlet” that responds with a “Hello, World!” message.


import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class HelloServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();
        out.println("<html><body>");
        out.println("<h1>Hello, World!</h1>");
        out.println("</body></html>");
    }
}

In this example, we extend the HttpServlet class and override the doGet() method to handle HTTP GET requests. We set the response content type to “text/html” and use a PrintWriter to write the HTML response.

Servlet Mapping

To use the “HelloServlet,” we need to map it to a URL pattern. This mapping can be done in the web.xml configuration file or using annotations, such as the @WebServlet annotation. Here’s how to do it using annotations:


import javax.servlet.annotation.WebServlet;

@WebServlet("/hello")
public class HelloServlet extends HttpServlet {
    // doGet() method as before
}

In this example, we’ve mapped the “HelloServlet” to the URL pattern “/hello.”

Servlet Container

Servlets are executed within a Servlet container, also known as a Servlet engine or Servlet runtime. Popular Servlet containers include Apache Tomcat, Jetty, and WildFly. The container is responsible for managing the lifecycle of Servlets, handling requests and responses, and ensuring that Servlets are thread-safe.

Servlets in a Web Application

In a typical Java EE web application, you package your Servlets, JSP (JavaServer Pages), HTML, and other resources in a web archive (WAR) file. The WAR file is then deployed to the Servlet container for execution.

Servlets vs. JSP

While Servlets are a powerful way to handle HTTP requests and generate dynamic web content, JavaServer Pages (JSP) are often used in conjunction with Servlets. JSP allows you to embed Java code directly within HTML templates, making it easier to generate dynamic content.

Conclusion

Java EE Servlets are essential components for building dynamic web applications. With their platform independence, request handling capabilities, and well-defined lifecycle, Servlets play a critical role in the Java EE ecosystem. As a developer, mastering Servlets is a fundamental step in web application development.

Java Language – 93 – Servlets