Writing Your First Bean 69 resources across a (Christian web host)
Writing Your First Bean 69 resources across a network. Some examples of directory service products are Directory Server (iPlanet), Active Directory (Microsoft), and Lotus Notes Domino Server (IBM). Corporations traditionally have used naming and directory services to store user names, passwords, machine locations, printer locations, and so on. EJB servers exploit naming services to store location information for resources that your application code uses in an enterprise deployment. These resources could be EJB home objects, enterprise bean environment properties, database drivers, message service drivers, and other resources. By using naming services, you can write application code that does not depend on specific machine names or locations. This is all part of the EJB location transparency, and it keeps your code portable. If you decide later that resources should be located elsewhere, your code does not need to be rebuilt because the naming service can simply be updated to reflect the new resource locations. This greatly enhances maintenance of a multitier deployment that may evolve over time. This becomes absolutely necessary when purchasing prewritten software (such as enterprise beans), because your purchased components source code will likely not be made available to you to change. While naming and directory servers have typically run standalone, they can also run in the same process as the application server. Many containers are written in Java, and so their naming and directory services are just bunches of Java classes that run inside of the container. Unless you re using CORBA, the de facto API used to access naming and directory services is JNDI, which we explain in Appendix A. JNDI adds value to your enterprise deployments by providing a standard interface for locating users, machines, networks, objects, and services. For example, you can use the JNDI to locate a printer on your corporate intranet. You can also use it to locate a Java object or to connect with a database. In EJB, JNDI is used to look up home objects. JNDI is also useful for locating resources across an enterprise deployment, including environment properties, database resources, and more; we ll show you how to leverage JNDI for these purposes in Chapter 10. How to Use JNDI to Locate Home Objects To achieve location transparency, EJB containers mask the specific locations of home objects from your enterprise beans client code. Clients do not hard-code the machine names that home objects reside on; rather, they use JNDI to look up home objects. Home objects are physically located somewhere on the net- work perhaps in the address space of an EJB container residing on machine #1, or perhaps on a container residing on machine #2. As a developer who writes client code to use beans, you don t care.
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