JavaEE stands for Java for Enterprise edition. JavaEE halps in enterprise grade applications. The enterprise grade applications are differentiated from desktop applications in terms of performance that is expected from them. An enterprise grade application have to deal with more than 1 user using it at the same time. So the issues of threading, performance, transaction, scalability is more pronounced here. Java, as part of JavaEE standards, provides technology stack which helps in building such applications.
When we are talking about JavaEE, we should also understand the concept of "Managed environment" very thoroughly. When we look back into the applications that we do for like desktop, one can realize that we control the main of application, which means we control the life cycle of the application. Also we are responsible for most of the time to create and release objects as per the need of the application. When we come to enterprise environment, the control changes. It can also be termed as Inversion of Control. The environment aids us in supporting many aspects of application. As a developer, one has to understand how to interact with this container. As a developer, we are responsible for writing the components as per certain specifications and the enterprise capability is provided by the environment. For example, take servlets. Servlet can help to build thread safe application for concurrent access (you have to little careful to handle certain things in certain way). As a developer, one is just responsible for writing the service method, which represents the business logic. But for deploying servlets we need a servlet container. Servlet containers represent our managed environment. The container provides the capability to create and destroy the object as per need and also provides multi threading capabilities. So when we are dealing with JavaEE technologies, its important to understand the concept of this managed environment and to learn how to interact with them.
The important technologies that are part of JavaEE are: