Normally, thinclient multitiered applications are hard to write because they involve many lines of intricate code to handle transaction and state management, multithreading, resource pooling, and other complex lowlevel details. The componentbased and platformindependent J2EE architecture makes J2EE applications easy to write because business logic is organized into reusable components and the J2EE server provides underlying services in the form of a container for every component type. Because you do not have to develop these services yourself, you are free to concentrate on solving the business problem at hand.
Containers and Services :
Component are installed in their containers during deployment and are the interface between a component and the lowlevel platformspecific functionality that supports the component. Before a web, enterprise bean, or application client component can be executed, it must be assembled into a J2EE application and deployed into its container.
The assembly process involves specifying container settings for each component in the J2EE application and for the J2EE application itself. Container settings customize the underlying support provided by the J2EE Server, which include services such as security, transaction management, Java Naming and Directory InterfaceTM (JNDI) lookups, and remote connectivity.
Container Types :
The deployment process installs J2EE application components in the following types of J2EE containers. The J2EE components and container addressed in this tutorial are shown in Figure 5. An Enterprise JavaBeans (EJB) container manages the execution of all enterprise beans for one J2EE application. Enterprise beans and their container run on the J2EE server. A web container manages the execution of all JSP page and servlet components for one J2EE application. Web components and their container run on the J2EE server. An application client container manages the execution of all application client components for one J2EE application. Application clients and their container run on the client machine. An applet container is the web browser and Java Plugin combination running on the client machine.