Component composition of Java EE applications and the advent of EJBS

1. Component composition of Java EE applications (distributed multi-tier application architecture)
Java EE applications are composed of components:
　　

When the client component communicates with the business logic component running on the server side, it can be accessed either directly or through the components of the Web tier, such as:

　　

The location of the SSH schema throughout the Java EE architecture:

After deployment, the Java EE components are installed on the Java EE server. Java EE servers provide Web containers and EJB containers. The EJB container manages the operation of the EJB, and the Web container manages the servlet and JSP runs.

　　

2. Java EE application Development and implementation process

In Java EE, a variety of different types of modules can be packaged separately, or they can be integrated into an ear package for deployment.

3, the general packaging rules
　　

4. Why EJB is used

The enterprise bean runs in the EJB container, which is actually a Java class that encapsulates the business logic. Reasons for using EJBs:

? Distributed!

Distributed objects collaborate with each other to accomplish specific business functions. Distributed transparency (or location transparency) should be achieved between the distribution objects. That is, there is no need to specify the location of the distributed object in the client code (resolved by configuration).

? transactional support between distributed objects (RMI does not support transactions)

? the application needs to support different clients

With only a small amount of code, the EJB can let the remote client access the Enterprise bean.

5. Summary

If your application requires a distributed deployment, if your distributed objects need to support transactions, and if your critical business logic needs to be able to support many different types of clients, then EJB will be a good choice.

Component composition of Java EE applications and the advent of EJBS