Java EJB Interview questions Part6

Question: Is an XSLT processor bundled in WebLogic Server?



Answer: Yes, we bundle an XSLT processor, based on Apache's Xalan 2.0.1 processor, in WebLogic Server 6.1.



Question: I plugged in a version of Apache Xalan that I downloaded from the Apache Web site, and now I get errors when I try to transform documents. What is the problem?



Answer: You must ensure that the version of Apache Xalan you download from the Apache Web site is compatible with Apache Xerces version 1.3.1. Because you cannot plug in a different version of Apache Xerces (see the preceding question), the only version of Apache Xerces that is compatible with WebLogic Server 6.1 is 1.3.1.



The built-in parser (based on version 1.3.1 of Apache Xerces) and transformer (based on version 2.0.1 of Apache Xalan) have been modified by BEA to be compatible with each other.



Question: How do I increase WebLogic Server memory?



Answer: Increase the allocation of Java heap memory for WebLogic Server. (Set the minimum and the maximum to the same size.) Start WebLogic Server with the -ms32m option to increase the allocation, as in this example:



$ java ... -ms32m -mx32m ...



This allocates 32 megabytes of Java heap memory to WebLogic Server, which improves performance and allows WebLogic Server to handle more simultaneous connections. You can increase this value if necessary.



Question: What causes Java.io exceptions in the log file of WebLogic Server?



Answer: You may see messages like these in the log file:



(Windows NT)



java.io.IOException Connection Reset by Peer



java.io.EOFException Connection Reset by Peer



(Solaris)



java.io.Exception: Broken pipe



These messages occur when you are using servlets. A client initiates an HTTP request, and then performs a series of actions on the browser:



1. Click Stop or enter equivalent command or keystrokes



2. Click Refresh or enter equivalent command or keystrokes



3. Send a new HTTP request.



The messages indicate that WebLogic Server has detected and recovered from an interrupted HTTP request.



Question: What is the function of T3 in WebLogic Server?



Answer: T3 provides a framework for WebLogic Server messages that support for enhancements. These enhancements include abbreviations and features, such as object replacement, that work in the context of WebLogic Server clusters and HTTP and other product tunneling.



T3 predates Java Object Serialization and RMI, while closely tracking and leveraging these specifications. T3 is a superset of Java Object. Serialization or RMI; anything you can do in Java Object Serialization and RMI can be done over T3.



T3 is mandated between WebLogic Servers and between programmatic clients and a WebLogic Server cluster. HTTP and IIOP are optional protocols that can be used to communicate between other processes and WebLogic Server. It depends on what you want to do. For example, when you want to communicate between



n A browser and WebLogic Server-use HTTP



n An ORB and WebLogic Server-IIOP.



Question: What are the enhancements in EJB 2.0 specification with respect to Asynchronous communication?



Answer: EJB 2.0 mandates integration between JMS and EJB.



We have specified the integration of Enterprise JavaBeans with the Java Message Service, and have introduced message-driven beans. A message-driven bean is a stateless component that is invoked by the container as a result of the arrival of a JMS message. The goal of the message-driven bean model is to make developing an enterprise bean that is asynchronously invoked to handle the processing of incoming JMS messages as simple as developing the same functionality in any other JMS MessageListener.



Question: What are the enhancements in EJB 2.0 with respect to CMP?



Answer: EJB 2.0 extends CMP to include far more robust modeling capability, with support for declarative management of relationships between entity EJBs. Developers no longer need to re-establish relationships between the various beans that make up their application -- the container will restore the connections automatically as beans are loaded, allowing bean developers to navigate between beans much as they would between any standard Java objects.



EJB 2.0 also introduces for the first time a portable query language, based on the abstract schema, not on the more complex database schema. This provides a database and vendor-independent way to find entity beans at run time, based on a wide variety of search criteria.