Is J# a part of J2EE?
Absolutely not! J# is a language developed by Microsoft. It's very
similar to Java in syntax and semantics. However, that's where the
similarity ends. Java can be compiled into bytecodes (class files) that run
on any platform. J# can only be compiled into code that runs on Microsoft
Windows platforms. J# is a part of Microsoft's .NET initiative.
What are J2EE design patterns? Are there any good sources regarding them?
If you're familiar with the term design patterns as it applies to
object-oriented programming, you'll find that EJB design patterns apply to
distributed Java programming using EJBs and other J2EE APIs. J2EE design
patterns describe patterns of solutions applied to similar problems in the
same context.
Some good sources for EJB and J2EE design patterns are EJB Design
Patterns by Floyd Marinescu; Core J2EE Patterns by Deepak Alur, John Crupi,
and Dan Malks;
http://developer.java.sun.com/developer/
technicalArticles/J2EE/despat; and
www.theserverside.com/patterns/index.jsp.
Does an entity bean always need a primary key?
Yes. An entity bean represents a row in a table in a relational
database. Each row in any RDBMS requires a primary key, which is the way to
store and retrieve the data stored in that row. Since an entity bean maps to
a row, it needs a primary key. The columns of the row (or the combination of
fields of the entity bean) that compose the primary key are defined in the
EJB's deployment descriptor.
Are there any official APIs for developing Web services in Java?
While there are different tools and app server vendors that give you the
ability to convert your Java components to Web services, Sun (the official
source) offers a set of APIs for Web services in Java in the form of a
toolset the Java Web Services Developer Pack (Java WSDP). Java WSDP allows
developers to build, test, and deploy XML applications, Web services, and
Web applications on the Java platform. The Java WSDP provides Java standard
implementations of existing key Web services standards, including WSDL,
SOAP, ebXML, and UDDI, as well as important Java standard implementations
for Web application development, such as JSP and the JSTL (JSP Standard Tag
Library).
What is EJB QL? How is it used?
Enterprise JavaBeans Query Language attempts to fill in the gaps between
the EJB model, which offers a standard way to access the database through
the object model, and SQL, which offers a much richer set of queries for
accessing RDBMS. EJB QL defines queries for the finder and for select
methods of an entity bean with container-managed persistence. EJB QL is a
subset of SQL92 and offers extensions that allow navigation over the
relationships defined in an entity bean's abstract schema.
EJB QL is not used inside the EJB classes. Rather, the queries are
defined in the deployment descriptor of the entity bean. The application
server deployment tool translates these queries into the corresponding SQL
that allows access to the database. The syntax of EJB QL is pretty much the
same as SQL syntax and should be easy to pick up for someone familiar with
SQL.
There seems to be a lot of UML design in EJB. Are there any APIs that allow
UML design to translate to EJBs?
Some of the IDE vendors such as Borland (JBuilder) and Rational offer
some capabilities to convert from one form to another. However, the
conversion is usually one-way and not always maintainable as the design
evolves. Currently there's a JSR 26 (Java Specification Request) called
"UML/EJB Mapping Specification" that describes a standard mapping between
the EJB architecture and UML.
