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EJB fundamentals and session beans
Create a scrollable virtual desktop in Swing
Wizard API updated!
Tim Boudreau has released a new version of the Swing Wizard library (version 0.997) that fixes the WizardException bug reported in JavaWorld's recent Open Source Java Project profile. The article's examples have been reworked to test out the new, improved WizardException. Thanks, Tim, for this helpful fix!
Open Source Java Projects: The Wizard API
Further, the runtime properties of the application components pertaining to transactions, persistence, security, and so on are customizable in the deployment environment, using the highly flexible declarative approach. The architecture defines a container and server model -- the container is the environment in which application component instances live and execute, while containers are in turn housed within a server. The J2EE platform thus provides a simplified development model, industrial-strength scalability, support for legacy integration, flexible deployment, application server and vendor independence, and generally tends to make proprietary application servers and proprietary distributed object frameworks almost archaic.
ejbCreate(), ejbRemove(), and so on, as well as the business methods; the Home interface; the Remote interface; and helper classes if necessary. The Home interface provides the signature for the methods that create, remove, and find EJB instances. The Remote interface defines the signatures for the business methods.
The focus of this article is on the Bean provider/EJB developer and the programming restrictions that apply to the EJB components' implementation code.
The following is a list of Java features that you should avoid, hence restricting their use in your EJB components' implementation code:
static, nonfinal fields. Declaring all static fields in the EJB component as final is recommended. That ensures consistent runtime semantics so that EJB containers have the flexibility to distribute instances
across multiple JVMs.
By restricting your use of features 10-16, you aim to plug potential security holes:
Policy, Security, Provider, Signer, and Identity).getEJBObject() available in SessionContext or EntityContext.
The restricted features listed above are, in fact, standard and powerful features of the Java programming language and the Java 2 Standard Edition (J2SE). The EJB container is allowed to make some or all of the restricted features from the J2SE unavailable to the EJB components -- by using the J2SE security mechanism rather than by subsetting the J2SE API set.
The Java 2 Platform Security policy for the standard EJB container of the EJB 1.1 specification defines the security permission
sets that concur with the programming restrictions on EJB components. According to the policy, several permissions such as
java.io.FilePermission, java.net.NetPermission, java.io.reflect.ReflectPermission, and java.lang.security.SecurityPermission are denied in order to enforce the programming restrictions listed earlier.
Some EJB containers may not enforce the restrictions with the expectation that the EJB developer will either adhere to the programming restrictions or violate them at his or her own risk. EJB components that violate those restrictions, by relying on fewer or more permissions than the standard set, will at the very least not be portable across EJB containers. In addition, indeterminate and unpredictable runtime problems could lie hidden in the code. That's all the more reason for EJB component developers to be aware of those programming restrictions and take special care to adhere to them.
Any violations of those programming restrictions within the EJB implementation code will not be detected at the time of compilation since those features are, after all, an integral part of the Java language and J2SE.
Those restrictions apply to EJB components as well as helper/access classes used by the EJB components. J2EE applications are packaged using the Java Archive (jar) file format into a file with an .ear extension (ear stands for Enterprise Archive). The ear file is the standard file format for delivering an application to the deployer. The ear file consists of EJB components in one or more ejb-jar files, and possibly library jar files on which the ejb-jars may depend. All code in that ear file is considered application code and is subject to the programming restrictions and permission sets.
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