Introduction to Java EE containers

1. Definition

A container is an interface between a component and the underlying service details. Before a Web component, an enterprise bean, and so on can be executed, it must be assembled into a Java EE module and deployed on a container. Such as:

　　

The assembly process mainly includes: Custom container transaction management features, Jndi services, etc. Of course, in Java EE, a variety of different types of modules can be packaged separately (JAR) deployed, or they can be integrated into an ear package for deployment.

2. Service

Java EE containers provide a variety of services in enterprise application development. For example, dealing with transaction management, managing the life cycle of EJBS and Servlets, database connection pooling, data persistence, and other underlying complex details.

3. Classification

We know that Java EE components are installed in the Java EE container after they have been deployed. First look at the component composition in Java EE project development:

　　

Based on component composition, the containers in Java EE Project development are divided into the following categories (top to bottom): Applet container, (applicationclient) Application client container, Web container, EJB container, such as:

　　

The main functions of the container are as follows:

? Apply the client container to manage the operation of the client application. For example, the application client container will provide JNDI services.

? Applet container, which manages the operation of applet applets.

? Web container to manage the operation of Servlets and JSPs.

? EJB container to manage the operation of the EJB.

4. Summary

The core concept of the Java EE is component + container, with more and more Java framework appearing, each of the corresponding framework has a corresponding container.

component, which means a unit of code that can be reused, generally represents one or a set of functional modules that can be separated, and there are many kinds of components in the Java EE, the common is client components, Web Components, EJB components, DAO components, etc. They have a common feature that will be packaged into. Jar,.war,.ear and other similar compressed file formats, each component is described by a specific format of the XML descriptor file, and the server-side components need to be deployed to the application server to be able to be used.

Introduction to Java EE containers