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What are JEE Containers? What are their different types?

Containers are the interface between a component and the low-level, platform-specific functionality that supports the component. Before it can be executed, a web, enterprise bean, or application client component must be assembled into a Java EE module and deployed into its container.

The assembly process involves specifying container settings for each component in the Java EE application and for the Java EE application itself. Container settings customize the underlying support provided by the Java EE server, including such services as security, transaction management, Java Naming and Directory Interface (JNDI) API lookups, and remote connectivity. Here are some of the highlights.

  • The Java EE security model lets you configure a web component or enterprise bean so that system resources are accessed only by authorized users.
  • The Java EE transaction model lets you specify relationships among methods that make up a single transaction so that all methods in one transaction are treated as a single unit.
  • JNDI lookup services provide a unified interface to multiple naming and directory services in the enterprise so that application components can access these services.
  • The Java EE remote connectivity model manages low-level communications between clients and enterprise beans. After an enterprise bean is created, a client invokes methods on it as if it were in the same virtual machine.
Because the Java EE architecture provides configurable services, components within the same application can behave differently based on where they are deployed. For example, an enterprise bean can have security settings that allow it a certain level of access to database data in one production environment and another level of database access in another production environment.

The server and containers are as follows:
  • Java EE server: The runtime portion of a Java EE product. A Java EE server provides EJB and web containers.
  • EJB container: Manages the execution of enterprise beans for Java EE applications. Enterprise beans and their container run on the Java EE server.
  • Web container: Manages the execution of web pages, servlets, and some EJB components for Java EE applications. Web components and their container run on the Java EE server.
  • Application client container: Manages the execution of application client components. Application clients and their container run on the client.
  • Applet container: Manages the execution of applets. Consists of a web browser and a Java Plug-in running on the client together.

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