BEA WebLogic Interview Questions and Answers 6

How do I use a third-party JDBC driver with JMS?
If your JDBC driver is not included in the list of drivers in the question about JDBC databases supported by WebLogic JMS, then the tables required by JMS must be created manually.

Note: WebLogic Server only guarantees support for the JDBC drivers included in the previous list. Support for any other JDBC driver is not guaranteed.

The .ddl files located in the weblogic/jms/ddl directory of the weblogic.jar file may be used as templates. Use the jar utility supplied with the JDK to extract them to the weblogic/jms/ddl directory using the following command:

jar xf weblogic.jar weblogic/jms/ddl

Note: If you omit the second parameter (weblogic/jms/ddl), the entire jar file is extracted.
Follow the procedures in JDBC Database Utility in Programming WebLogic JMS to manually create the database tables for the JDBC store.
Another option is to consider using a file store instead of a JDBC store. File stores are easier to configure and may provide significantly better performance.

The Multicast TTL setting for a cluster in the WebLogic Admin console sets which of the following values?
a. Maximum time taken for multicast messages to reach their final destination
b. The number of routers a multicast message can pass through before the packet can be discarded
c. The multicast address to be used by the messages sent from the cluster
d. Minimum time taken for broadcasting a multicast message from the cluster

Choice B is correct. The Multicast TTL(TTL-Time to Live) setting specifies the number of routers a multicast message can pass through before the packet can be discarded. To configure the multicast TTL for a cluster, you should change the Multicast TTL value in the WebLogic Server administration console. This sets the number of network hops a multicast message makes before the packet can be discarded.
If you choose to distribute a cluster over a WAN (or across multiple subnets), you must plan and configure your network topology to ensure that multicast messages are reliably transmitted to all servers in the cluster. One of the requirements to be met by the network is that the multicast Time To Live (TTL) value must be high enough to ensure that routers do not discard multicast packets before they reach their final destination.

Which of the following algorithms is used by the WebLogic Server as the default load balancing strategy for clustered object stubs when no algorithm is specified ?
a. Round-robin
b. Weight-based
c. Random
d. None of the above

8. Choice A is correct. The basic idea behind load balancing is that by distributing the load proportionally among all the servers in the cluster, the servers can each run at full capacity. WebLogic Server clusters support several algorithms for load balancing clustered objects. The particular algorithm you choose is maintained within the replica-aware stub obtained for the clustered object. Configurable algorithms for load balancing clustered objects are: Round-robin, Weight-based and Random.
WebLogic Server uses the round-robin algorithm as the default load balancing strategy for clustered object stubs when no algorithm is specified. Round-robin is the only load balancing strategy used by WebLogic proxy plug-ins for HTTP session state clustering. The round-robin algorithm cycles through a list of WebLogic Server instances in order. For clustered objects, the server list consists of WebLogic Server instances that host the clustered object. For proxy plug-ins, the list consists of all WebLogic Servers that host the clustered servlet or JSP.

How do I use persistence?
Use the following guidelines:
1. Make sure the JMSServer you are using has a store configured. The JMSServer configuration entry in the config.xml file should contain a line of the form

Store=""

Note that if JMS boots without a store configured, it is assumed the customer did not want one, and persistent messages are silently downgraded to non-persistent (as specified for JMS 1.0.2).

2. Make sure you are not using "Message.setJMSDeliveryMode". This is overwritten, as it is a vendor-only method.

3. Make sure you are calling either:

QueueSender.send(msg, deliveryMode, ...)

-- or --

QueueSender.setDeliveryMode(deliveryMode)

-- or --

set the DefaultDeliveryMode mode on connection factory in the config.xml file to persistent (the QueueSender.setDeliver/send overrides this value). Similarly, for topics, you would set this via the TopicPublisher.

4. Make sure you don't have "DeliveryModeOverride" set to Non-Persistent on the Destination in the config.xml file.

5. If you are using pub/sub, only durable subscriptions persist messages. Non-durable subscriptions have no need to persist messages, as by definition they only exist for the life of the server.

6. If you are using JDBC, the JDBC tables, JMSSTATE and JMSSTORE, are created automatically when the JMS server boots. The DDL files used to create the tables are stored in weblogic.jar in weblogic/jms/ddl. The example configuration below shows a JDBC store for Oracle (client version 8.1.7 or later is needed to run with WLS 6.1 on JDK 1.3). To manually create the tables (also deleting any existing tables), run java utils.Schema as described in the previous question.

See the question, "How do I start WLS and configure JMS?" for a description of how to configure JMS.

Here is a sample config.xml file resulting from configuring JMS. It should look similar to yours. If you want JMS to use a file store instead of a database, just change JDBCStore to FileStore in the JMSServer section.
ListenPort="7001" DefaultProtocol="t3"
ThreadPoolSize="8" >

GuestDisabled="false" />
FileRealm="defaultFileRealm" />
<FileRealm Name="defaultFileRealm"
/>
TemporaryTemplate="TestTemplate1"
Targets="myserver" Store="JDBCStore">
JNDIName="jms.queue.TestQueue1"
Template="TestTemplate1"
/>

<JMSTemplate Name="TestTemplate1"
/>
<JMSFileStore Name="FileStore"
Directory="myfilestore"
JMSServer="TestJMSServer"
/>
ConnectionPool="testpool2"
JMSServer="TestJMSServer"
/>
<JDBCConnectionPool Name="testpool2"
Targets="myserver"
URL="jdbc:weblogic:oracle"
DriverName="weblogic.jdbc.oci.Driver"
InitialCapacity="0"
MaxCapacity="1"
CapacityIncrement="1"
Properties="user=SCOTT;password=tiger;server=bay816"
/>


The following is a sample class that sends
a Topic message on construction:

import javax.naming.*;
import javax.jms.*;
import java.util.Hashtable;

public class t

{
public final static String DESTINATION="jms.topic.TestTopic1";

private TopicConnectionFactory connectionFactory;
private TopicConnection connection;
private TopicSession session;
private TopicPublisher producer;
private TextMessage message;
private Topic destination;

public t()
{
try {
Hashtable env = new Hashtable();
env.put(Context.INITIAL_CONTEXT_FACTORY,
"weblogic.jndi.WLInitialContextFactory");
env.put(Context.PROVIDER_URL, "t3://localhost:7001");
InitialContext ctx = new InitialContext(env);
destination = (Topic) ctx.lookup(DESTINATION);
connectionFactory = (TopicConnectionFactory)
ctx.lookup("javax.jms.TopicConnectionFactory");
connection = (TopicConnection)
connectionFactory.createTopicConnection();
session = (TopicSession) connection.createTopicSession(false,

Session.AUTO_ACKNOWLEDGE);
producer = (TopicPublisher) session.createPublisher(destination);
producer.setDeliveryMode(DeliveryMode.PERSISTENT);
message = (TextMessage) session.createTextMessage();
message.setText("hello world");
producer.publish(message);
} catch (Exception e) {
}
}
}