According to EJB specification, EJB can not directly use file. So we have to find a way to read/write file indirectly. There are some solution for this.
1. We can use RMI technology.
2. We can use JCA to read file.
Solution 1:
RMI is the way to read file. It is also easy to implemented. All we have to do is make a server which provide a service: read/write file. EJB will implement a client to communicate with this server. All data when read/write file between the EJB and RMi Server is in byte array. But one of the drawback is that RMI is so heavy and big.
Solution 2:
The J2EE Connector architecture is based on the technologies defined and standardized in the Java 2 Platform, Enterprise Edition (J2EE) and is part of the J2EE platform.
As more businesses move towards an e-business strategy, integration with existing enterprise information systems (EIS) becomes the key to success. Enterprises with successful e-businesses need to integrate their existing EIS systems with new web-based applications. They also need to extend the reach of their EIS systems to support business-to-business (B2B) transactions.
Before the the J2EE Connector architecture was defined, no specification for the Java platform addressed the problem of providing a standard architecture for integrating heterogeneous EIS systems. Most EIS vendors and application server vendors use non-standard vendor-specific architectures to provide connectivity between application servers and enterprise information systems. The following diagram illustrates the complexity of a heterogenous environment.
The Java 2 Platform, Enterprise Edition provides containers for client applications, web components based on Servlets and JavaServer Pages (JSP) technologies, and Enterprise JavaBeans (EJB) components. These containers provide deployment and runtime support for application components. They also provide a federated view of the services provided by the underlying application server for the application components.
Containers run on existing systems: web servers for the web containers, application servers, transaction processing (TP) monitors, and database systems for EJB containers. This enables enterprises to leverage both the advantages of their existing systems and those with J2EE technology. Enterprises can write (or rewrite) new applications using J2EE technology capabilities and can also encapsulate parts of existing applications with Enterprise JavaBeans or JavaServer Pages (JSP) technologies.
Enterprise applications access functions and data associated with applications running on EISs. Application servers extend their containers and support connectivity to heterogeneous EISs. Enterprise tools and Enterprise Application Integration (EAI) vendors add value by providing tools and frameworks to simplify the EIS integration task.
The J2EE Connector architecture defines a standard architecture for connecting the J2EE platform to heterogeneous EIS systems. Examples of EIS systems include ERP, mainframe transaction processing, database systems, and legacy applications not written in the Java programming language. By defining a a set of scalable, secure, and transactional mechanisms, the J2EE Connector architecture enables the integration of EISs with application servers and enterprise applications.
The J2EE Connector architecture enables an EIS vendor to provide a standard resource adapter for its EIS. The resource adapter plugs into an application server, providing connectivity between the EIS, the application server, and the enterprise application. If an application server vendor has extended its system to support the J2EE Connector architecture, it is assured of seamless connectivity to multiple EISs. An EIS vendor needs to provide just one standard resource adapter which has the capability to plug in to any application server that supports the J2EE Connector architecture.
Multiple resource adapters (that is, one resource adapter per type of EIS) are pluggable into an application server. This capability enables application components deployed on the application server to access the underlying EIS systems.
Now all we have is implemented ResourceAdapter to provide a File Service to EJB. It is so tricky. But it works.
