Java EE Benefits and Servlets Overview

Java EE Benefits

• Ensures high availability to support continuous operation of applications.
• Offers scalability to accommodate growing workloads and user demands.
• Facilitates integration with existing systems for seamless operation.
• Provides freedom to select vendors, tools, and application servers.
• Supports a multi-platform approach for cross-environment compatibility.
• Enhances flexibility for various scenarios and diverse client types.
• Improves programming productivity through reusable components and tools.

Introduction to Servlets

• A servlet is a Java component designed to extend a web server’s capabilities by providing custom services.
• Servlet Container (or web container) manages servlets and handles their lifecycle. Example: Apache Tomcat.

Servlet Life Cycle

• Consists of init(), service(), and destroy() methods that manage servlet operations.
• init(): Initializes servlet, called once during its lifecycle for setup.
• service(): Core method for processing client requests, can invoke doGet() or doPost().
• destroy(): Cleans up resources when the servlet is taken out of service, called once.

Ancillary Methods of Servlets

• getServletConfig(): Retrieves servlet-specific configuration information and parameters.
• getServletInfo(): Provides metadata about the servlet, useful for documentation.

Handling Dynamic Requests

• Begins when a user interacts with a link directing to a servlet.
• Security and integration features improve resilience and connectivity in web development frameworks.

Enterprise JavaBeans (EJB)

• An EJB represents a framework for developing large-scale distributed business applications on the Java platform.
• Requires an EJB Container (e.g., WildFly, GlassFish) for key services like lifecycle management and security.

When to Use EJB

• Ideal for applications needing remote access across diverse locations.
• Supports scalability through load balancing and clustering.
• Separates business logic from presentation, allowing cleaner architecture.

Advantages of EJB

• Reusability: Components easily integrated into various applications (e.g., Visual Age).
• Visual Development: EJBs can be visually combined using IDEs to enhance productivity.
• Facilitates multithreading for resource efficiency.
• Simplifies database access (e.g., JDBC) and network communications (e.g., RMI).
• Provides transaction management, easing manual coding efforts.
• Offers well-defined interfaces for interaction between different EJBs.

EJB Types

• Session Beans: Perform tasks for clients categorized as:
  • Stateless: No maintenance of client-specific state across calls.
  • Stateful: Maintains state for specific client over multiple calls.

Servers Overview

• A server responds to client requests over a network; types include:
  • Web Server: Delivers static content (e.g., HTML).
  • Application Server: Runs applications and business logic.
  • FTP Server: Manages file transfers.
  • Online Game Server: Supports multiplayer gaming environment.

Web Server vs. Application Server

• Web Server: Delivers web pages and serves static content via HTTP.
• Application Server: Handles dynamic content and manages business logic with various protocols (e.g., RMI).

Java EE Servers and Containers

• Java EE Server: Runtime component providing EJB and web containers.
• EJB Container: Manages EJB execution.
• Web Container: Oversees execution of web pages and servlets.
• Application Client Container: Executes client components.
• Applet Container: Manages applet execution through a web browser.

Java EE Services

• Messaging: Java Message Service (JMS) enables asynchronous messaging.
• Transaction: Implemented by Java Transaction API (JTA) for transaction management.
• Persistence: Managed by Java Persistence API (JPA) for ORM and database operations.
• Web Service: JAX-RS and JAX-WS support REST and SOAP services.
• Contexts & Dependency Injection: CDI promotes loosely coupled resource injection.