When you design a Java EE application, one of the first decisions you make is the type of client access allowed by the enterprise beans: remote, local, or web service.
Whether to allow local or remote access depends on the following factors.
Tight or loose coupling of related beans: Tightly coupled beans depend on one another. For example, if a session bean that processes sales orders calls a session bean that emails a confirmation message to the customer, these beans are tightly coupled. Tightly coupled beans are good candidates for local access. Because they fit together as a logical unit, they typically call each other often and would benefit from the increased performance that is possible with local access.
Type of client: If an enterprise bean is accessed by application clients, then it should allow remote access. In a production environment, these clients almost always run on different machines than the Enterprise Server. If an enterprise bean’s clients are web components or other enterprise beans, then the type of access depends on how you want to distribute your components.
Component distribution: Java EE applications are scalable because their server-side components can be distributed across multiple machines. In a distributed application, for example, the web components may run on a different server than do the enterprise beans they access. In this distributed scenario, the enterprise beans should allow remote access.
Performance: Due to factors such as network latency, remote calls may be slower than local calls. On the other hand, if you distribute components among different servers, you may improve the application’s overall performance. Both of these statements are generalizations; actual performance can vary in different operational environments. Nevertheless, you should keep in mind how your application design might affect performance.
If you aren’t sure which type of access an enterprise bean should have, choose remote access. This decision gives you more flexibility. In the future you can distribute your components to accommodate the growing demands on your application.
Although it is uncommon, it is possible for an enterprise bean to allow both remote and local access. If this is the case, either the business interface of the bean must be explicitly designated as a business interface by being decorated with the @Remote or @Local annotations, or the bean class must explicitly designate the business interfaces by using the @Remote and @Local annotations. The same business interface cannot be both a local and remote business interface.