Weblogic Server Interview Tips to Remember
WebLogic Server is the first e-commerce transaction platform to implement advanced J2EE features. To comply with the rules governing J2EE, BEA Systems provides two separate downloads: one with J2EE features enabled. Both downloads offer the same container and differ only in the APIs that are available. Here are some of the important Interview Tips to Remember for Weblogic Server Administration.
1) While packaging the Web Application DefaultWebApp for deployment into the WebLogic server, the home and remote interfaces of the enterprise beans used by the servlets should reside in which directory?
A) When packaging a web application create META-INF and WEB-INF subdirectories in the application directory to hold deployment descriptors and compiled Java classes. All servlet classes and helper classes should reside in the WEB-INF/classes subdirectory. The home and remote interface classes for enterprise beans used by the servlets into the WEB-INF/classes subdirectory. All the HTML files, JSP files, images, and any other files that these Web pages reference should exist in the application directory, maintaining the directory structure for referenced files. The META_INF directory contains the deployment descriptors for the enterprise beans, but not the classes.
2) How do I set up my CLASSPATH?
A) Setting up your CLASSPATH correctly depends on what you are trying to do. The most common tasks are described below:
* Starting WebLogic Server. See Setting the Classpath Option in the Starting and Stopping WebLogic Servers section of the Administration Guide. In addition, your WebLogic distribution includes shell scripts that you can use to start the server. These scripts, which are located in the domain directories under the config directory of your WebLogic Server distribution, automatically set up the CLASSPATH variable in the shell before starting the server.
3) Why do I get the following exception when viewing the JNDI tree?
The Weblogic Server JNDI implementation requires objects to be serializable, not referencable. A PrintWriter cannot be serialized and therefore should be declared transient.
4) How do stubs work in a WebLogic Server cluster?
A) Clients that connect to a WebLogic Server cluster and look up a clustered object obtain a replica-aware stub for the object. This stub contains the list of available server instances that host implementations of the object. The stub also contains the load balancing logic for distributing the load among its host servers.
5) How is security handled in the WebLogic J2EE Connector Architecture?
A) Due to the fact that the current configuration and packaging requirements for resource adapters in WebLogic Server require the hand-editing of the weblogic-ra.xml file, any new passwords specified in the security-principal-map entries are done in clear-text.
BEA understands the importance of protecting security passwords. Hence, we provide a Converter Tool that allows for the encryption of all passwords present in the weblogic-ra.xml file. The Converter Tool is shipped in the standard weblogic.jar file.
6) Can I enable requests to a JDBC connection pool for a database connection to wait until a connection is available?
A) No, there’s no way to allow a request to wait for a pool connection, and from the system point of view there should not be. Each requests that waits for a connection ties up one of the fixed number of execute threads in the server, which could otherwise be running another server task. Too many waiting requests could tie up all of the execute threads and freeze the server.
7) How do I use multibyte character sets with WebLogic jDriver for Informix?
A) Currently, multibyte character sets are not supported for the WebLogic jDriver for Informix driver.
8) How do I connect to an SQL Server instance that is running on a machine with multiple instances of SQL Server 2000?
A) Each instance of MS SQL Server must be listening on a different port. So, you can use the port number in the properties that you pass to the getConnection() method or, in case of connection pools, you can specify the port property in the following properties:
To find the port number where each MS SQL Server instance is running, run the server network utility (in the Microsoft SQL Server program group), select the server instance, select TCP/IP, and click the properties button.
9) Why does FOR UPDATE in Oracle 8 cause an ORA-01002 error?
A) The Oracle 8 server generates an ORA-01002:fetch out of sequence error message when you use a FOR UPDATE statement with AUTOCOMMIT turned on (which is the default state when using JDBC). This is known to happen on Oracle 8.0 and 8.1 on Solaris and on Oracle 8.1 on Windows NT. If you turn AUTOCOMMIT off, you will not receive this error. Because this problem is due to a change in the Oracle 8 server, you should contact Oracle support for more information.
10) What causes an OCIW32.dll error?
A) You may receive the following error message when using your JDBC driver for Oracle: “The ordinal 40 could not be loaded in the dynamic link library OCIW32.dll.” This problem is caused by an out-of-date version of OCIW32.DLL in your system directory. Some programs install this file in the system directory in order to run. If you remove this file from the system directory you should no longer receive this error.