EJB Fundamentals 49 beans, and even who is (Photography web hosting)
EJB Fundamentals 49 beans, and even who is allowed to use each method on a particular bean. You can also specify what security roles the beans themselves should run in, which is useful if the beans need to perform secure oper ations. For example only bank executives can call the method to create new bank accounts. In EJB, a deployment descriptor is an XML file. You can write these XML files by hand, or (if you re lucky) your Integrated Development Environment (IDE) or EJB container will supply tools to generate the XML deployment descriptor. In the latter case, you simply might need to step through a wizard in a Java IDE to generate a deployment descriptor. As a bean provider, you are responsible for creating a deployment descriptor. Once your bean is used, other parties can modify its deployment descriptor settings. For example, an application assembler who is piecing together an application from beans can tune your deployment descriptor. Similarly, a deployer who is installing your beans in a container in preparation for a deployment to go live can tune your deployment descriptor settings as well. This is all possible because deployment descriptors declare how your beans should use middleware, rather than you writing code that uses middleware. Declaring rather than programming enables people without Java knowledge and without source code access to tweak your components at a later time. This paradigm becomes an absolute necessity when purchasing EJB components from a third party because third-party source code is typically not available. By having a separate, customizable deployment descriptor, you can easily fine-tune components to a specific deployment environment without changing source code. Vendor-Specific Files Since all EJB server vendors are different, they each have some proprietary value-added features. The EJB specification does not touch these features, such as how to configure load-balancing, clustering, monitoring, and so on. Therefore, each EJB server vendor may require that you include additional files specific to that vendor, such as XML files, text files, or binary files. Ejb-jar File Once you ve generated your bean classes, your home interfaces, your remote interfaces, and your deployment descriptor, it s time to package them into an Ejb-jar file. An Ejb-jar file is a compressed file that contains everything we have described, and it follows the .ZIP compression format. Jar files are convenient, compact modules for shipping your Java software. Figure 2.7 shows the Ejb-jar file creation process.
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