Accessing EJB components with Delphi client

Absrtact: This paper analyzes the principle of COM clients accessing EJB components using COM bridge, and gives an example of using Delphi to access the EJB components deployed on WebLogic server. Finally, several other integration schemes and optimization strategies using this scheme are compared and analyzed.

Keywords: COM, EJB, distributed components

1. Overview

CORBA,. NET, Web Service, and Java EE are the achievements of distributed software architecture respectively. Java-EE is superior to CORBA in model simplicity, while eliminating it. NET dependence on a company, relative to the Web service technology it is relatively mature and therefore in the industry has an important position. The core of Java EE is the EJB (EnterPrise Java Bean)-a distributed component.

The client of an EJB component can be a web-style applet,jsp/servlet, or a GUI customer that is not web-style. Because of the popularity of PC GUI customers are often windows-based. Delphi is the next excellent development platform for Windows, and Borland offers elegant solutions to EJB access on BAS (Borland's EJB server) (CORBA is used concurrently on both the client and server side). However, there is no solution for Delphi to the EJB components deployed on other servers. Sun developed the Java-EE CAS COM Bridge Solution to the problem of client access to EJB components by COM (Common Object Component, Microsoft's proposed component model). Delphi fully supports COM technology, so Delphi can serve as an EJB customer. This article focuses on how to use Delphi to access EJB components.

Java EE CAS com Bridge (hereafter referred to as COM bridges) is a bridge software provided by Sun, through which customers who can use any of the development tools of COM technology can successfully access the EJB components on the Java server.

As shown in Figure 1.1, Java EE CAS com bridge starts the JVM (Java Virtual machine) in the customer application address space, and COM bridges provides an external COM component that wraps the JVM into COM components that customers use to access the JVM. Thus, when a client makes a COM call, the COM bridge forwards it to the process JVM,JVM using JNI (Java Native Interface) to send the call to the service program (the RMI/IIOP protocol is used to send the request when accessing the Java server). That is, the client's call eventually becomes a real Java invocation, and the process of implementing the transition in the middle is done by the COM bridge without the developer's concern. It is the same principle to access the local Java object and access the EE server.