Web Logic Server Interview Questions And Answers

EJB is used with the web logic server and provides the mechanism of remote method invocation using the JAVA API’s. The support is extended to CORBA that is used to transport these remote calls using RMI/IIOP protocols. This interface provided flexibility and performance by increasing the development of the application. EJB supports the local interface mechanism to allow streamlined calls to the bean if a caller is in the same container. This doesn’t include any overhead that is usually involved with RMI when using the marshalling feature. The interfaces provide the foundation for the container managed relationships between the entity beans.

T3 provides a framework for WebLogic Server messages this includes the necessary support for the enhancements of the services that needs to be given. T3 framework includes certain features like object replacement and tunneling concept used in the clustering of the web logic servers. T3 uses Java Object Serialization and RMI, to provide the object and communication from one server to another server remotely. T3 is a framework that connects the web logic server with the programmatic clients. T3 uses protocols such as HTTP and IIOP to communicate between the processes and web logic servers.

• Start web logic server and go to console.
• Select JMS, to configure anything create a store and create a new JMS file.
• Create a new connection and add it to the JDBC connection pool.
• Select the target server. Select the template that needs to be applied on the JMS.
• Select a server or create a new JMSServer, this server will consist of the JMS that will be booted when the system or the server will be turned on.
• Create destinations in which the query from the JMS server will get stored.
• Create connection factories by typing in the name and JNDI name. The targets can be selected from here to deploy the connection factory.

Open the web logic server console and select ACLs in the tree view. To configure the JMS security there is a need to create a control list. The procedure is as follows:
1. Set ACL name like weblogic.jms.queue.QUEUENAME or weblogic.jms.topic.TOPICNAME.
2. Create it with new permission that include send and receive permissions.
3. Create users of groups list and set the permissions for it. Save the changes of implementation and exit.
The procedure will update the fileRealm.properties file with the statements given below: acl.send.weblogic.jms.queue.myQueue=user
acl.receive.weblogic.jms.queue.myQueue1=user

Web logic server supports the JDBC drivers that are included and with other databases as well. The JDBC drivers if not present then the JMS has to be created manually. If it is present then it just has to be included. The files that are used having .ddl extension that is located in weblogic/jms/ddl directory of the weblogic.jar file and this can be used as a template. The jar utility that is supplied can be extracted with JDK using the following command:
jar xf weblogic.jar weblogic/jms/ddl
After the extraction the drivers gets copied to the specified location and then they can be inserted in the application by going the console. This will automatically create the database tables for the JDBC store. This is easier to configure and provide better performance in compare to other methods.

This function is used in EJB to call ConnectionFactory.getConnection() that connects to the EIS. It is a part of the Resource adapter and the application server. This is called to listen to an event that is taking place on the entire server whose data is present. This allows the connection to be established between the two servers and used to get the connection details for the new server. This function manages all the connections that are in the list and adds the connection whenever there is a requirement and the need.

The security is quite strict when it comes to add new servers or update an existing one. The current configuration includes the information of all the connections that are established with the main server and it consists of the packaging requirements for the resource adapters in web logic servers. The server provides password protection and encryption method to increase the security of the overall standards. All the passwords are present in the file weblogic-ra.xml. The web logic server provides a converter tool that allows the information to be encrypted and made password protected. This converter tool is present in standard weblogic.jar file.

The resource files are represented in CLASSPATH and the resource adapters are also mentioned there. The server instance includes the deployment of EJB and resource adapter in the form of .rar file format. The EJB consists of no dependencies as it is being written on the common client interface (CCI). EJB client is used to communicate with one another and it consists of message sending mechanism. EJB is having the parameter classes that are defined in .rar file format. EJB uses the class loaders also maintaining a hierarchy that is defined in the .rar specific class. When the instance is being passed as an argument to the EJB the application server de-serialize the object and sends the message to the servers of its deactivation.

There are two databases that can be used with the Web logic J2EE connector architecture and these databases are as follows:
1. Cloudscape database: This is the default database that is used with the architecture and this consists of the samples that contain the resource adapter representing the database system. The configuration of this is set in weblogic-ra.xml file that contains the cloudscape datasource.
2. Oracle database: The settings of cloudscape can be replaced by oracle settings. The resources that are provided consist of the JDBC support, hence it can use any database for which the resources can be configured and represented.

The steps involved in setting up the CLASSPATH in web logic server are as follows:
• Start the web logic server and open the setting option where the CLASSPATH is being mentioned. This includes the option of starting and stopping the web logic server.
• Open the web logic distribution shell script and start the server. The script is located in the config directory and it is used to set up the CLASSPATH variable automatically as soon as the server script starts.
• While compiling the application classes or using the web logic utilities, the CLASSPATH can be set and right entries can be made to the configuration file.

There are various configurations that have to be made to make the weblogic server run on multiple machines. The methods that are involved have their advantages and disadvantages. The Web logic server consists of no built-in limit for the number of instances it can have in a cluster, but it can consists of larger number of instances if it is having multiple clustered systems. The web logic servers are best deployed to use more than one server instance at a time. Multiple machine can have one cluster each and have a synchronization method to increase the distribution of server instances.

To setup the Oracle instance of the OS Authentication feature. The steps that have to be followed are:
1. Open the INIT[sid].ORA file from the config directory of the web logic server.
2. Add the line OS_AUTHENT_PREFIX = OPS$ in the file INIT[sid].ORA file and as the statements are case sensitive so the statements should be written as it is.
3. Open the database of Oracle server by using the credentials of the SYSTEM.
4. Create a user using the name of OPS$userid, where userid is the name of operating system loginID. Grant the full privileges to the user for connection and using the resources on the server.
5. After setting up the connection with the made user then the Web logic jDriver for Oracle can be connected by using the “/” as the username property and “” as the password property. The example is given below:

$ java utils.dbping ORACLE "/" "" userserver
Properties props = new Properties();
props.put("user", "/");
props.put("password", "");
props.put("server", "userserver");
Class.forName("weblogic.jdbc.oci.Driver").newInstance();
Connection conn = myDriver.connect("jdbc:weblogic:oracle",props);

The connection pool attribute can be accessed using the administrative console of the connection pool. This includes the Web logic jDriver for Oracle and JDBC connection pool configuration for setting up the attribute for overall server system. The example that is given below show the attribute that is been accessed in the web logic server:
<JDBCConnectionPool
Name="userPool"
Targets= “userserver,server1"
DriverName="weblogic.jdbc.oci.Driver"
InitialCapacity="1"
MaxCapacity="10"
CapacityIncrement="2"
Properties="databaseName=userOracleDB"

Web logic jDriver for Oracle returns a Java object that includes the data and the information for retrieval. The object that is returned from ResultSet.getObject() is as follows:
• A double is returned for the column types of Number(n) and Number(m,n). If the precision that is defined is not accurate then it can be represented by using the BigDecimal as well.
• If the column type is a NUMBER then the Java type that has to be returned based on the actual value of each row. The values in this type may vary from one row to another row.
These are the type of objects that are returned by using the data variables in the Web logic server.

The stored procedure are the procedures that is called when a function need to use some internal variables. These variables are used to access the relational database system and used to play a big role in web logic server. The code that is given below shows the same:

CallableStatement cstmt = conn.prepareCall("Begin procName; END;");
cstmt.execute();
//procName is the name of an Oracle stored procedure.
//The above statement is the standard oracle statement that works with the Oracle DBMS. // The following syntax given below will call the stored procedure.
CallableStatement cstmt = conn.prepareCall("{call procName};");
cstmt.execute();
// This is the syntax which will work with all the database system.

The PreparedStatement class allow to bind the string values in the class. The setString() method that can be used with it won’t work due to incompatibility. The example shows the usage of the PreparedStatement:

String pstmt = "select n_name from n_table where n_name LIKE '?%'";
PreparedStatement ps = conn.prepareStatement(pstmt);
ps.setString(1, "Rohit");
ResultSet rs = ps.executeQuery();

This PreparedStatement doesn’t work due to the fact that the value needs to be specified in a string and not be embedded in quotes. The corrected statement that gets executed is as follows:
String matchvalue = "rohit%";
String pstmt = "select n_name from n_table where n_name LIKE ?";
PreparedStatement ps = conn.prepareStatement(pstmt);
ps.setString(1, matchvalue);
ResultSet rs = ps.executeQuery();

What are web logic servers?
What are servers?
What are the prerequisites of starting a server?
Explain briefly the client-server architecture.
Explain how a web logic server works?
In a web logic server what is the domain?
What are the common domain types?
Explain the tier architecture of a web logic server?
What are logics in reference to web logic servers?
What are the differences between a web logic server and a web server?

How will a single machine run multiple web logic server instances?
In web logic how are new threads assigned?
Define the list of pre-configured queues?
Define managed servers?
What is an administration server?
What are application servers?
What are the advantages of using application servers?
What are middleware servers?
What are the uses of a middleware server?
What are class paths? how can they be set?

In web logic what is the MSI code?
What is the format of a log message in a web logic server?
What is the format of the Log message out to standard out?
Name the various message severity levels in web logic?
What is a trace in relation to web logic server?
What is the emergency log message?
Arrange in order the various message severity levels?
How is the logging implementation specified in web logic?
What are log filters and what are their purpose?
How can domain configuration lock be enabled and disabled?

What is the difference between Dynamic and Non-dynamic changes in the console?
Define the purpose of the SerializedSystemini.dat file?
In what ways can a web logic servers performance be improved upon?
What is WLST in web logic?
What are the different modules of WLST? Explain?
Explain briefly what is the NM?
What are the different versions of NM?
How can the NM be made to work with web logic? Explain?
What are the different groups under web logic security?.
What is the role of a deployer?

What are crossdomainconnectors in reference to web logic servers?
How is a domain template created?
Can struck threads be killed manually?
What is the difference between Txdatasource and Datasource?
Define the functions of T3 in the web logic server?
What are stubs and how do they function in a web logic cluster?
What elements make up the administration console?
Define the toolbar elements.
What does the connected to element in the toolbar signify?
What is the tree view pane in the web logic server?

The two mechanism of the server that it uses to find out the unavailability of the server, in the same way it uses the same mechanism to find out the new added server in the cluster. The web-logic server broadcasts a message to all the servers that are available and the servers in return respond to the message to show their availability to the server. If any new server is added then it also sends a message, a check is made to check the list of all the available server instances and if there is no result found then the server is made available in the list. There always remain stubs that monitor the cluster periodically and update the list of available server instances.

The DNS request is made to the failed servers also. When the main server send the request to all the servers to notify their availability then the client looks the server instance using the JNDI lookup and search by using the object reference. This allows the user to find out the new server instance and it will then be passed to the stub that monitors the cluster and the list of the clusters gets updated and it shows the availability of the servers as well. If the request is made to the server that is failed then it can be handled by using the third party load balancer like Resonate, BigIP, etc. These products are used to mask multiple addresses in a single address and return the result. This helps in keeping the track of all the servers.

The web-logic servers use two different mechanisms to find out the unavailability of the servers. The servers that are unavailable won’t be having any use and it is a good practice to find out and neglect them. These mechanisms are as follows:
1. Weblogic server instance gets stored in a cluster and uses multicast to broadcast the messages over the server and send a message to the main server for its availability. The main server monitors the messages of the server instances if any of the servers fails to respond.
2. Weblogic server monitors the errors that is corresponding to the socket on which the server is communicating and try to determine the availability from there. If the socket is open then the server sends the message to the main server and the communication happens. If there is no message and the socket gets closed unexpectedly then the server is assumed to be offline.

In case of any failure that is occurring in the stub then the stub doesn’t have any information and it faces the difficulty to connect it to the web-logic servers also. The stub remains in connection with the server instances and allow it to be started during the booting of the system. The stub consists of the server instances list as well that allow the server to communicate with one another. If there are no servers that in communication then the stub uses DNS to find the running server and obtain the list of running instances of the server. The stub refreshes itself to obtain the list and take advantage of the new server that is attached to the cluster.