Web Logic Server Interview Preparation Guide

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The purpose of OS authentication in connection pool is to use the UserIds of the user to start the appropriate web logic server. OS authentication is the operating system service that is allowed to authenticate the login information of the user. The database security is one of the issues for the web logic servers, so OS authentication is a necessary feature in operating systems. The connection pool and the database can be accessed if the client connection is established. Oracle uses the process of OS authentication while the accessing of the database. The JDBC driver of web logic allows only the user to take control over the databases.

To allow the use of Unicode codesets certain changes has to be made within the web logic jDriver. The following steps allow the setup to be done:

1. Install the appropriate codeset with the installation of Oracle.
2. Define the environment variable and NLS_LANG variable in the environment to allow the synchronization happen between the JDBC driver and Oracle supported drivers or the codesets.
3. Assign proper codeset to NLS_LANG in the shell of the WebLogic Server.
4. Restart the database services and server services to check whether everything got properly installed. When installed use it according to the requirements.

The transaction isolation levels that are supported by the servlets application using the Oracle database include the BLOB fields. The web logic jDriver can be installed and used, but if due to some reason the code fails to execute then it shows an error message and also there are some levels in which the messages are divided and these are as follows:
SET TRANSACTION ISOLATION LEVEL READ COMMITTED
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
The Oracle database supports only these two levels of isolation. When used with Web logic’s drivers it throws an exception for the drivers that are unsupported. There are some drivers that ignore the attempts to be set an unsupported isolation level.

The following error OCIW32.dll is received while using the Oracle with JDBC driver. The error states that the dynamic library couldn’t be loaded in the system and this happens due to outdated OCIW32.dll driver that is residing the system. The program usually called as updater updates the program in the system directory and to installs it to run in the system. The error can be removed by removing the system directory. This is also due to the incompatibility of some drivers with the JDBC. The JDBC allows the connection of more than one database, so this might cause the error. eive this error.

The multi-byte character sets are not supported by the Web logic jDriver that in turn used for the Informix driver. But, the support for it is added in the codeset of web logic jDriver. The multi-byte characters are used in a multi-user environment application. This gets confirmed first and a check is made to see whether the file is corrupted or not. The command that is used to check is bcheck or secheck. These come as a utility. If the files integrity is being verified then the table is being formed consisting of the data that is required by the client. A lock can be provided for the use of multi-byte characters in the database and the table.

The multi-pools are used to store the connection in 2 levels inside the pool and configure it accordingly. There are two ways in which the Multi-pools can be set up:
1. The multi-pool can be made as a backup if the connection to the database event fails.
2. The multi-pool can be setup as a load balancing server that will allow the server to give away some load to alternative server to balance the work and give higher performance. The multi-pools are used in the configuration of Web logic JDBC features and allow it to be chosen according to the requirements of the server from time to time.

The problem with the servers is to have few resources or the database connection in the connection pool to decrease the work load. The servers need to increase the maximum number of connections in the connection pool and utilize it to balance the overall load on the server. The server needs to be optimally designed to allow the connection pool to execute few threads and get the work done. The application should be designed to find out whether there are connections available or not. If there are connections available then it shows the message of NoResourceException. This is shown by the example:
try{
// your statement
} catch(Exception handleEx) {
// your statement
} finally {
try{ conn.close();
}catch (Exception ignore){} // this returns the connection pool
}

The purpose of the stub is to contain the object of the server and use it to connect it to the Web-logic server cluster. The cluster consists of more than one object that is residing on the server and consists of the replica of the object. The stub consists of the available server instances that is used to host the implementation of the objects and used to run the web-logic server as well. The stub also consists of the information that is related to loading of the server and load balancing of it. This load balancing allows the server to distribute the load among its host servers so that it never fails to provide data to the users.

ClassFormatErrors are used in the applet when the setup is not being properly set or the path to which the file is pointed is incorrect.
<APPLET
CODEBASE=http://your_server/webz/ns-home/classes
CODE=applets.myapp.class>

This happens due to change in the file format of CODEBASE in the Weblogic server. The Codebase tag should point to the HTTP server and not on the weblogic server. The path that is referenced by the CODEBASE tag is should not be the absolute directory path that is on the HTTP server and it should be configured properly to the Document root of the HTTP server. The above code should be changed with the code given below:
<APPLET
CODEBASE=http://your_server/classes
CODE=applets.myapp.class>

The safest way to modify config.xml is to do it from the Web-logic server administration console. While doing from this also the things that has to be kept in mind is that:
• Save a copy of the config.xml before making any modification to the original file. If there is any modification that causes error then it can prevent the web logic server also to start up. There is a possibility to revert back to the saved version of the file.
• Manually editing of the config.xml file, for a particular domain when, it is not active. If any changes are being made when the file is under use then those will be overwritten by the system. Any invalid XML or attribute value will be detected and the server won’t be able to boot. The information will be stored in this file.