Java Servlets Certification Training (beginner to advanced)

¡Hola! It seems like you've provided a comprehensive list of topics and objectives for learning about Java Servlets, as well as an overview of the Java Servlet architecture and its life cycle. Let's break down each part and elaborate a bit more on the points you've mentioned to ensure a solid understanding of Java Servlets.

Understanding Java Servlets

Java Servlets: These are Java programs that interact with HTTP servers (servlets API is specified by the Java Community Process as part of JAX-ASBAPI). They handle requests from clients and return responses to them.

Servlet Interfaces:

• Servlet: The root interface for all servlet types. It has a single method service(ServletRequest, ServletResponse) which is used to handle HTTP requests and responses.
• GenericServlet: Extends Servlet and provides implementations for lifecycle methods like init() and destroy().
• HttpServlet: Extends GenericServlet and provides support for common HTTP functions, such as doGet(), doPost(), etc.

Annotation and Xml based configuration: Modern servlets use annotations to specify initialization parameters, while the web.xml file is used for older styles of configuration.

Difference between Get & Post:

• GET requests are used to retrieve data from specified resources; the data is appended as a query string to the URL.
• POST requests are typically used to send data to be processed (e.g., form data submitted to a server).

Servlet Life Cycle:

1. Loading: The servlet container loads the servlet class when it receives a request for the servlet, or when it's explicitly loaded (e.g., during startup).
2. Initializing: The init() method is called once per instance to initialize the servlet.
3. Request Handling: The service method processes each request and produces an appropriate response. For HttpServlet, you override methods like doGet(), doPost(), etc.
4. Destroying: The destroy() method is called when the servlet instance is no longer needed.

Load On Startup Configuration: This is specified in the web.xml file and defines which servlets should be loaded when the application starts.

Request Scope: Servlets have different scopes, but the request scope is specific to a single HTTP request and is often used to pass information between the client and the servlet for that request.

ResponseDispatcher interface: This interface allows a servlet to include additional servlets in its responses, effectively passing control to another servlet.

Interservlet communication: Can be done using RequestDispatcher to forward or include other servlets, or by storing data in the session, etc.

ServletConfig: An interface that allows a servlet to retrieve its initialization parameters and perform dynamic class loading.

ServletContext: A shared context across all servlets and filters within an application, providing access to application-wide data.

Session Tracking: Can be managed using cookies or URL rewriting, storing session attributes in the HttpSession object.

Filters in servlets: Filters are used to log requests, share common code among multiple servlets, or perform common processing like compression or encryption.

Database connection: JDBC is commonly used in servlets for database interaction.

CRUD operations: Create, Read, Update, and Delete operations can be implemented within a servlet to interact with a database.

Events and Listeners: The ServletContext interface provides methods for adding and removing listeners that respond to events related to the lifetime of an application.

Steps to Create Servlet

1. Create a directory structure: Place your Java classes within the WEB-INF/classes directory or zip it into a .war file.
2. Create a Servlet: Extend HttpServlet and override its methods as needed.
3. Compile the Servlet: Use javac to compile your servlet code.
4. Add mappings to the web.xml file: Configure your servlet with the appropriate mapping, class name, and initialization parameters.
5. Start the server and deploy the project: Launch your application server (e.g., Tomcat, Jetty) and deploy your application containing the servlets.
6. Access the servlet: Use a web browser or tool like curl to request the servlet's URL.

By following these steps and understanding each component of Java Servlets, you'll be well-equipped to create robust web applications using servlets in a Java environment. Remember that as of Java 9, the term "servlets" has been deprecated in favor of "JAX-RS RESTful Web Services" for REST APIs and "JavaServer Pages (JSP)" for server-side page generation. However, many applications still use traditional servlets, especially when integrating with legacy systems or when performance is a critical concern.