What is the function of application servers if servlet containers exist?

Application servers provide broader capabilities compared to servlet containers. They include:

• Support for distributed transactions (JTA): Managing transactions that span multiple resources (databases, message queues).
• Management of EJB (Enterprise JavaBeans) lifecycle: Components for creating scalable, distributed, and reliable enterprise applications.
• Support for JMS (Java Message Service): Integration of systems through asynchronous messages.
• Integration with JNDI (Java Naming and Directory Interface): Centralized management of naming and resource access.
• Security management (JAAS - Java Authentication and Authorization Service): A unified model for authentication and authorization for all application components.
• Support for other enterprise-level technologies, such as JCA (Java EE Connector Architecture) for legacy system integration, and WebSocket for bidirectional communication.

Servlet containers mainly handle HTTP request processing and manage the lifecycle of servlets and JSPs. Application servers include a servlet container, adding other necessary services to build comprehensive enterprise applications.