Enterprise Java Servlets Overview

Study Notes

Enterprise Java and Servlets

Enterprise Java, commonly known as J2EE (Java 2 Enterprise Edition) and now referred to as Java EE (Java Enterprise Edition), is a platform that enables the development of large-scale, robust, and secure web applications. At the heart of these applications lie servlets, a powerful technology for handling HTTP requests and generating responses.

Servlet API

The Servlet API is a Java specification that defines classes, interfaces, and methods for processing HTTP requests and generating responses. It forms the core of Enterprise Java's web application stack, providing a standardized way for web servers to handle HTTP requests and interact with Java code.

Servlet Interface

The Servlet Interface is a contract between the server and the servlet. It defines a set of methods that servlets must implement to process requests and generate responses. This interface provides a consistent way for servlets to interact with the server and handle HTTP requests.

Servlet Type

The Servlet API defines three types of servlets:

Generic Servlet (GenericServlet): This is the base class for all servlets and provides basic implementation for the Servlet API's methods.
Http Servlet (HttpServlet): This class extends GenericServlet and adds methods for handling HTTP requests and responses.
JSP Servlet (JspServlet): This class is used to process JSP files and generate dynamic content.

Servlet Life Cycle

The Servlet API defines a life cycle for servlets, which consists of four stages:

Load: The servlet is loaded by the server.
Initialize: The server calls the init() method in the servlet to initialize any resources it uses.
Service: The server calls the service() method in the servlet to handle HTTP requests and generate responses.
Destroy: The server calls the destroy() method in the servlet to release any resources it used.

Servlet Request

The Servlet API provides the HttpServletRequest class to represent HTTP requests. This class provides methods to retrieve request parameters, headers, and other relevant information.

Servlet Response

The Servlet API provides the HttpServletResponse class to represent HTTP responses. This class provides methods to send response headers, generate content, and otherwise manage the response.

Http Servlet Req uest and Http Servlet Response

As mentioned earlier, the HttpServletRequest and HttpServletResponse classes are used to handle HTTP requests and generate responses, respectively. These classes extend ServletRequest and ServletResponse, adding functionality specific to HTTP protocol.

Request Dispatcher

The Servlet API provides the RequestDispatcher class to forward or include requests between servlets. This class allows for modular and reusable application design.

Servlet Config

The Servlet API provides the ServletConfig class to pass configuration information to a servlet. This class is used to initialize the servlet and provides methods to retrieve configuration parameters.

ServletContext

The Servlet API provides the ServletContext class to access shared data and resources. This class allows servlets to share data and access resources such as JavaBeans and web application properties.

Session Tracking

The Servlet API provides session tracking capabilities, allowing a web application to maintain a session with a client by using cookies or URL rewriting. This feature enables stateful applications and improves the user experience.

Servlet Filter

The Servlet API provides the javax.servlet.Filter interface to intercept and modify requests and responses. This interface is used to implement cross-cutting concerns, such as security, caching, and logging.

Servlet Input Stream

The Servlet API provides the ServletInputStream class to read data from requests. This class is used to read request data, such as uploaded files.

Servlet Output Stream

The Servlet API provides the ServletOutputStream class to write data to responses. This class is used to send response data, such as HTML pages and images.

Understanding these components and their interactions is essential for developing robust and scalable web applications using Enterprise Java and servlets.

Description

Explore the core concepts of Enterprise Java and servlets, including the Servlet API, servlet types, life cycle, request handling, response generation, and more. Learn about servlet configuration, session tracking, filters, and input/output streams.