BEA WebLogic Interview Questions and Answers 4

Why do I get an error while trying to retrieve the text for ORA-12705?
This error occurs when you have not set the ORACLE_home environment variable properly — a common mistake. In order to use WebLogic jDriver for Oracle, the Oracle client software needs to be installed and ORACLE_home must be set.
You may also see this error message if you try to use WebLogic jDriver for Oracle's internationalization capabilities with a language/codeset combination that is not installed on your system. If you get the ORA-12705 error with the correct error text, then either you have set NLS_LANG improperly, or you do not have the right codesets installed on your system.

Why do I run out of resources during updates with Oracle's database link?
When you use Oracle's database link to update your database, you may get error "maximum number of temporary table locks exceeded" even if you close your result sets and statements when you finish.
The database link is an object in the local database that allows you to access tables, views, and such in a remote database. The database link is controlled by the Oracle server, so the driver has no control over its use of resources. The link appears to perform the commit (since other processes could see the records that were being created), but it doesn't free any resources until the connection is closed. The solution is to remove the database link and use the JDBC driver to do your selects, inserts, and updates.

How do I prevent errors when running t3dbping?
When you are testing your Oracle database connections under UNIX, you can run SQL*PLUS and can successfully ping the database using utils.dbping. However, when you use the multitier utils.t3dbping utility, you receive an ORA-12154 error message.

First, make sure that your ORACLE_home environment variable is correctly set to point to your Oracle installation. This variable must be set in the environment where the WebLogic server is running.

In the C-shell issue the following command:
$ setenv ORACLE_home path

where path is the path to your Oracle installation.
In the Bourne shell, issue the following commands:
$ ORACLE_home=path
$ export ORACLE_home

Where path is the path to your Oracle installation. When you ping your database using the two-tier utils.dbping utility, the JDBC driver loads the database client library and establishes the connection to the database. When you use the multitier utils.t3dbping utility, the WebLogic Server loads a two-tier driver and uses it to establish a database connection. In both cases, the same method is used to connect to the database. SQL*PLUS works because it doesn't require ORACLE_home to find the client libraries.

If you are still experiencing problems, try this:
1. Open a command shell.
2. Run the two-tier version of utils.dbping in this shell.
3. Start WebLogic in this shell from the command line:
$ java -ms32m -mx32m weblogic.server
4. Open a second command shell.
5. Run the utils.t3dbping in the second shell against the server running in the first command shell.
If this procedure doesn't work, please send the output from these commands to WebLogic technical support.

Why does executing the PreparedStatement class cause a "TRUNC fails: ORA-00932: inconsistent datatypes" error?
According to Oracle Metalink Bug Database Doc ID: 144784.1, in the absence of explicit data typecasting, OCI assumes that a bind variable is a CHAR data type. If the SQL statement intends to use the bind variable as a DATE data type, but OCI thought it was a CHAR, the SQL parser will have a conflict in data types. The fix is to explicitly use data conversion functions to convert the bind variables in the problem queries. For example, a select string of
String st = "select count(*) from simple_table where
TRUNC(mydate) = TRUNC(?)";


should be changed to:
String st = "select count(*) from simple_table where
TRUNC(mydate) = TRUNC(TO_DATE(?))";

Why am I getting an "ORA-01000: maximum open cursors exceeded" error, even though I closed all ResultSet, Statement, and Connection objects?
This is an Oracle issue. According to Oracle's documentation, dynamic cursors can remain open from run to run in a session and are not closeable when a procedure closes. To work around this issue, you can increase the number of open cursors allowed in the database or you can reset the connection pool (close and reopen database connections in the connection pool).
To reset the connection pool, you can untarget and retarget the connection pool using the Administration Console. You can also use the reset() method through the JMX API or the RESET_POOL command on the WebLogic Server command line interface.

An instance of stateful session EJB when accessed simultaneously from more than one clients on same VM results in RemoteException or EJBException. In case the client is a Servlet thread, which of the following techniques can be used to avoid RemoteException/EJBException?
a. Not possible.
b. Store the reference to the EJB instance as an instance variable of Servlet class.
c. Store the reference to the EJB instance as a local variable of Servlet class.
d. Make the Servlet client to be remote instead of internal to WebLogic server.

Choice C is the correct choice. An instance of a stateful session EJB can be accessed from only one client virtual machine at a time. Multiple client threads from the same virtual machine can access the same instance of a stateful session EJB, but they must do so in a serial fashion. If a client-invoked business method is in progress on an instance when another client-invoked call, from the same or different client, arrives at the same instance of a stateful session bean class, the container may throw the java.rmi.RemoteException to the second client , if the client is a remote client, or the javax.ejb.EJBException, if the client is a local client. Thus choice D is incorrect.
To avoid any exception, each Servlet should store a reference to a particular EJB instance in a local variable of the Servlet's service() method. Please note that variables local to methods like service(), doGet(), doPost() are not shared between different requests and are automatically thread safe. Thus choice C is correct. An instance variable unlike local variable is shared. Thus Choice B is incorrect.
An implication of this rule is that an application cannot make loop back calls to a session bean instance.
This restriction does not apply to a stateless session bean because the container routes each request to a different instance of the session bean class.

Are there C/C++ interfaces to WLS JMS?
No, this is not supported.
* Write your own interfaces using JNI.
* Setup a Servlet that your C/C++ client calls to generate a JMS message. You should spawn multiple threads in C++ and use multiple posts to pass messages via http.

How do I start WLS and configure JMS?
On Windows, start WLS 6.X by selecting Start -< Programs -< BEA WebLogic E-Business Platform -< WebLogic Server 6.X -< Start Default Server and enter the administrator password.

On Windows, to configure JMS, start the console by selecting Start -< Programs -< BEA WebLogic E-Business Platform -< WebLogic Server 6.X -< Start Default Console.

1. In the console tree view on the left, select JMS.

2. If you want persistent messages, first create a Store - Select Stores. In the window on the right, Select Create a new JMSFile Store for a file store, give it a name, give it a directory, select create. If you want a JDBCStore, you first need to create a JDBC connection pool by selecting JDBC in the tree view, Connection Pools, create a new JDBC Connection Pool. Select Targets, select a Target server, select the arrow that points to the right and select Apply. Then go back to Stores, Create a new JMSJDBCStore.

3. If you want to use a template, first create a Template - Select Templates. You need a template to create temporary queues. Select Create a new JMS Template, give it a name, select create, then you can move to the Thresholds &Quotas tab or the Override tab. Select Apply when done with your changes.

4. Select Servers. Select Create a new JMSServer, give it a name, select a Store if you created one, select a template if you created one, Select Create. Now you can move to the other tabs, make changes, select Apply. In particular, you must select Targets, select a Target server, select the arrow that points to the right, and select Apply. This is the server on which JMS will boot.

5. Create Destinations - from the tree view in the left panel, select the + in front of JMS, select the + in front of Servers, select the + in front of your server, select Destinations, Select Create a new JMSQueue or Create a new JMSTopic, fill in the first page and Select Create, then you can select, fill in, and Apply other tabs.

6. Create Connection Factories - on left tree view, open JMS. Select Connection Factory. Select Create a new JMS Connection Factory on the right panel. Type in the name and JNDI name. Select Create (lower right hand corner). Select the Targets tab. Select the name of the server on which you want to deploy the connection factory. Select the arrow pointing to the right - the server moves to chosen. Then select Apply (lower right hand corner).

How do I configure JMS security?
The correct way to set up security for JMS is to go to the console, select ACLs in the tree view, then create some access control lists.
1. Set the ACL name which should be weblogic.jms.queue.QUEUENAME or weblogic.jms.topic.TOPICNAME.
2. Select Create.
3. Enter the New Permission of send or receive.
4. Select Create.
5. Enter a comma separated list of users or groups.
6. Select Grant Permission.
7. Select "saved to the realm implementation" to save your changes.
8. Select Yes.
This will update the fileRealm.properties file with lines that look like the following:
acl.send.weblogic.jms.queue.TestQueue1=user1
acl.receive.weblogic.jms.queue.TestQueue1=user1
If you don't have an ACL for a queue or topic, security is wide open.
There are also ACL's for accessing the JNDI context; the JNDI context is a requirement for initially accessing JMS. See the JNDI documentation.