Development of the business reservation system based on EJB technology

The technology has been applied to the development of large-scale network system more and more, the author will introduce the definition of EJB (Enterprise Java Beans), the structure model of application system based on EJB technology and the content and classification of EJB component. Finally, a business reservation system is developed with EJB based structure model and EJB component.
EJB is technically not a "product", but a technical specification. Sun's definition of EJB is that the EJB structure is a component structure for developing and configuring a distributed business application based on components. Applications developed with EJB architecture are scalable, transactional, and multi-user-safe. These applications may only be written once, but can be configured on a task server platform that supports the EJB specification. In general, EJB is a standard server-side component model for component transaction monitoring.

The system structure model based on EJB technology
The EJB structure is a service-side component structure, a hierarchical structure, and its structural model is shown in Figure 1. The structure model can be divided into the customer layer, the business logic layer and the data layer under normal circumstances, and the following author makes a brief introduction.

Figure 1: An application architecture model based on EJB

The customer tier is primarily designed to meet the various access requirements for the entire system and to handle the following tasks:
The user input can also be analyzed and checked and processed accordingly.
Displays the results of the run from the server-side hierarchy.
The customer layer is typically composed of customer processes that are dynamically created and revoked by the browser.

Business Logic Layer This is the most critical part of the entire system. The business logic layer is typically divided into two tiers, the high-level of which is the request-receiving layer (commonly called the web layer), which receives requests from the browser and sends the request to the underlying process, sending the request processing results to the browser. These processes consist primarily of JSP pages, web-based applets, and servlets that display HTML pages. The underlying level is the request processing layer (commonly called the EJB layer), this includes monitoring processes, process processes, and database operation processes that handle and process client requests from the receiving layer, as well as passing the request results to the request layer and, if necessary, handing the results to the data tier for storage.
The data layer is mainly for the business logic layer to provide data services, such as the storage business logic layer processing results, return to the business logic layer of data retrieval results, but also in order to achieve the shielding data source changes, so that when the database changes we only need to modify the statement connected to the data source.

Classification of EJB components
Typically, there are two basic types of EJB components on the server side: the Entity bean (entity Bean) and the session bean.

Figure 2: Architecture of the Business reservation system

Entity beans are models built for real-world objects that are typically persistent records of a database. The Entity Bean builds a model for business concepts that can be expressed as nouns, describing both the state of real-world objects and their behavior, while allowing developers to encapsulate data and business rules related to specific concepts. The session bean is a enterprise bean,session bean instance that is created through the home interface and is proprietary to the client connection and is not generally shared with other clients. The session bean is an extension of the client application and is responsible for managing the entire process or task. The session bean can manage the interactions between entity beans, describing how they work together to accomplish a special task.
Entity beans can be divided into container-managed beans and bean-managed beans, depending on how you manage persistence. Container-managed beans are automatically managed by the EJB container for their persistence, the container knows how the bean instance's fields are mapped to the database, and automatically manages to insert, UPDATE, and delete entity-related data in the database; the beans that manage persistence with beans need to do all of this explicitly. The bean's developer must write code to manipulate the database, and the EJB container will tell the bean instance when it is safe to insert, update, and delete data in the database, and in addition, it does not provide any other help. The bean instance completes all the persistence work itself.
The session bean can be divided into stateless beans and stateful beans based on whether they are stateful. Stateless session beans tend to be generic and reusable; A stateful session bean is an extension of the client application that represents the customer's completion of the task and maintains the customer's related status.

Development of Business Reservation system
The cabin reservation system is a commercial reservation system based on EJB component technology developed on the Java platform, the main process is that after the user login, will be led in turn through the Customer Selection page and navigation Selection page, And will select a available cabin for the customer (get a list of available cabins from Traveagentbean, Travelagentbean's Listavailablecabin () method is invoked by the servlet that generates this page. The cabin list will be used to mount the HTML list box on the Web page of the user's browser, and when the user selects a cabin and submits a selection, an HTTP request is sent to the EJB server (Websphere application Server), and the server receives the request Assign it to Reservationservlet, the servlet calls the Travelagent.bookpassage () method to make the actual subscription, and the label information returned by the Bookpassage () method is used to create another Web page that is sent back to the user's browser. If the reservation is successful, the payment method in Processpaymentbean is invoked by Processpaymentservlet to achieve the billing process for the customer. The specific framework is shown in Figure 2.
The EJB components in the scheduled system mainly include the following sections:
Cabinbean: Entity Bean, the primary key is CABINPK, an entity bean used to encapsulate the real-world ship cabin.
Customerbean: Entity beans, primary keys are CUSTOMERPK, an entity bean that encapsulates the real-world consumer who needs to book a ship's cabin.
Cruisebean: Entity Bean, the primary key is CRUISEPK, is an entity bean that encapsulates the shipping routes in the real world. Reservationbean: Entity Bean, the primary key is Cruiseid,cabinid, which represents the unchanging record in the database, a reservation, which records the historical events of the reservation system, mainly to prevent double bookings, that is, two customers booking the same flight in the same cabin, This problem arises because there is a period of time between when the customer chooses the cabin and the route and when the Bookpassage () method is invoked. Travelagentbean: Stateful session Bean, a session bean that is responsible for booking a sailing class workflow, encapsulates the process of completing a subscription operation for a route and is used in the client applications of travel agents around the world. Travelagentbean not only meets the needs of consumers to book tickets, but also provides information on the remaining cabins during the voyage. In order to complete this task, the bean needs to know which route, cabin, and customer make up the reservation, and after collecting this information, the Bookpassage () method is used to complete the processing of the booking process, which is responsible for billing the customer account, and booking the selected cabin on the correct vessel on the correct route. And through the ticket class to produce a ticket for the customer. Here, we need to use the CreditCard class to store information about the customer's credit card, and the Listavailablecabins () method is used to display the available cabins that are not yet booked.
Processpaymentbean: Stateless session bean, which is the process of charging consumers in a transaction system. It defines three transaction methods for checking, cash, and credit card payments, namely Bycheck (), Bycash (), and Bycredit ().

Program code examples for business reservation systems
The development of the entire business reservation system was developed under IBM VisualAge for Java, where entity beans are much easier to develop than session beans, and the following is a travelagentbean example of the development process for EJB components:

1. Travelagent Remote Interface
It provides a way to set up the routes and cabin IDs that customers want to book. In addition, the Boolpassage () method is set up to charge the customer's subscription and generate a ticket for the customer. The specific code is as follows:
package com.titan.travelagent;
Import java.rmi.RemoteException;
Import javax.ejb.FinderException ;
Import com.titan.cruise.Cruise;
Import Com.titan.customer.Customer;
Import Com.titan.processpayment.CreditCard;
Public Interface Travelagent extends Javax.ejb.EJBObject
{
public void Setcruiseid (int cruise) throws Remotee Xception, finderexception;
public int Getcruiseid () throws RemoteException, Incompleteconversationalstate;
public void Setcabinid (int cabin) throws RemoteException, finderexception;
public int Getcabinid () throws RemoteException, Incompleteconversationalstate;
public int Getcustomerid () throws RemoteException, Incompleteconversationalstate;
Public Ticket boolpassage (CreditCard card,double price) throws RemoteException, Incompleteconversationalstate;
}

2. Travelagent Home Interface
The Travelagent Home Interface code is as follows:

Puckage com.titan.tracelagent;
Import java.rmi.RemoteException;
Import javax.ejb.CreateException;
Import Com.titan.customer.Customer;
Public interface Travelagenthome extends Javax.ejb.EJBHome {
Public travelagent Create (Customer Cust) throws remoteexception,createexception;}

3. Travelagent Bean Class
It needs to implement the Travelagent remote interface and all the behavior in the home interface, limited to space, this article will no longer introduce its implementation code, interested readers can do it themselves.

With the above steps, we have completed the development of an EJB component for a business reservation system.