JBOSS Interview Questions and Answers - JBOSS FAQ

What are the components that are used in Jboss Cache?

Jboss cache is used as a replicated and transactional cache. It is said like that due to the fact that multiple Jboss cache instances can be distributed in java virtual machine or each virtual machine will have its own copy of it. These cache can reside on the same machine or different machines that is on the network. This keeps the replicated data across the network in case any failure arises. The transactional property is due to the fact that user can create and configure a compliant transaction manager and make their own cache operations. If the cache is not replicated then it is running in a local mode and it has two components that are involved:

1. Generic cache : It has internal implementation and the method can be used as org.jboss.cache.TreeCache
2. POJO cache : Is also implemented internally by using the method as: org.jboss.cache.aop.PojoCache. It extends the functionality of Tree.
3. TreeCache : Is used to represent a tree like cache that provides easy replication and transaction properties to extend the functionality of the object cache. It provides a transparent mapping tool to map it to the internal cache.

What are the steps that are involved in deploying Jboss cache using Mbean service?

JBoss cache provides MBean service that can be registered with the environment to allow the cache access using JMX. The steps that are involved in deploying JBoss cache that is using Mbean service is that:

1. First copy the configuration xml file and deploy it in the directory that is given by the JBoss cache. The configuration files from all other sections are present there only.
2. Check the etc/META-INF directory for the configuration files that are for different cache modes and that can be used to deploy the JBoss cache.
3. Get the command to invoke the right service like create, start, stop, and destroy operations t be performed on the files given in the directory.
4. Look for the details of the cache’s current state to see the process which can be executed or contained before any other.
5. Cache configuration files are checked and necessary changes are made when the cache is already running.

What is the procedure to access the JBoss Cache MBean service?

To access the MBean service the JBoss sets the server using many header files like Proxy files, Server locater files, cache configuration files etc. The sample code given below explains the procedure.
org.jboss.mx.util.MBeanServerLocator;
org.jboss.mx.util.MBeanProxyExt;
org.jboss.cache.TreeCacheMBean;
javax.management.MBeanServer;

MBeanServer server;
TreeCacheMBean cache;
// These are the header files that are given above. It consists of all the files like server files, MBean service files, cache configuration files, etc.
public init() throws Exception
// This is the start function by which the process starts
{
try
// This is the exception handling block to find the errors at runtime
{
       server = MBeanServerLocator.locateJBoss();
       cache = (TreeCacheMBean) MBeanProxyExt.create(TreeCacheMBean.class, "jboss.cache:service=TreeCac
}
catch (Exception ex)
{
       // handle exception
}
}

What are the main directories provided in JBoss?

The main directories that are provided in JBoss directory structure are as follows:

1. bin – It consists of system executable and normal files that are for execution purpose. It consists of binary files for every program that is installed on the system.
2. client – It consists of all the configuration files that are stored and jar files that can be required by the Java client application.
3. docs – It consists of the XML documents with the DTDs for the reference. These documents provide the basic specification related to the installation and deployment of JBoss.
4. lib – This consists of jar files that are required to run the JBoss microkernel. This is directory is not for any user as it consists of the kernel and system libraries.
5. server – This consists of different server configuration files. The files are in the script format.

What are the different types of services provided by JBoss server?

The services of the server are based on the type of files that are provided and kept by the server. The server provides the service from basic to advanced and they are classified as:

1. Core services : These are the services that provide scripts to start the server and provide the basic functionality of the start-up scripts.
2. Logging Service : These are the services that are used for logging on the server and using the configuration setting to modify and create it.
3. Security Service : These are the services that all the security domain information to be stored in the file login config.xml files and used to list the named security domain features. It specifies all the separate modules that are used for authentication purpose in the domain.
4. Additional Services : These are the services that are hot-deployable and directly deployed in the directory. They consist of XML descriptor files and other resource files.

What are the core services provided by the JBoss server?

The core services are specified in the configuration files that are used by the JBoss. This file lies in the configuration folder. The file is called as service.xml and it is the first file that starts when the server gets started. This file consists of the configuration MBeans for various services including the logging, security, etc. The example of the file is given as:
<!--
name="jboss:service=JNDIView"
xmbean-dd="resource:xmdesc/JNDIView-xmbean.xml">

-->

This way a service can be stopped and modified and this effect when the server gets restarted. It doesn’t list the services that are removed in the service management console.

What are the Logging Services provided by the JBoss server?

The logging server allows the user to log into the server and save its logging details which might be used again. The package that is used for logging is log4j. The logging onto a server is controlled from a central file that resides in the configuration file that is managed separately. The file name I given as log4j.xml and this file defines a set of appending files that also considered as log files. The file follows a specific format that should go with the message and there is also a filtering option that is used to filter out the details that are not required. The output of this file gets to both the console and a log file that is also called as server log given in the log directory. Logging services are very important to manage as it keeps the defined data on the server of people who are logging in.

What are the different types of log levels that are used in logging services in JBoss?

There are four different types of log levels that are used to show the services that are present inside the logging in JBoss. The log levels are as follows:

1. Debug : In this level the file gets debugged for possible errors. This can either be automatic or manual as it doesn’t affect the file in any way.
2. Info : At this level the complete detail information is provided about the process that is running in the background. It consists of details like name of the process, CPU usage, etc.
3. Warn : At this level the warning that has come in the file that might hinder the performance on some systems are given and it is displayed with some critical signs to aware the user to see the warning and take necessary actions if required.
4. Error : At this level during the compilation of the error there are some errors shown that can be syntactical error or logical errors. These errors have to be fixed before completing the compilation process.

What is meant by logging threshold in JBoss?

The logging threshold is given as INFO as it is a level on which all the informational messages, warning messages and error messages on the console are produced and shown, but not the debug messages. It is managed through the file as there is no threshold set for the server.log file. The generated logging messages will be stored in that section to provide all the information from one place. The log files are always checked in case of any errors that are produced due to some information on the debug messages that can help in tracking down the problem. The logging threshold allows the debug messages to be displayed with the complete information about the log files. The logging limits are set for individual categories.

Write a program to show the change in level in JBoss server.

If the change in the level has to be set from INFO to DEBUG level then the output from the container-managed persistence engine has to be changed to the DEBUG level. A redirection takes place in separate files and a log is maintained with the name cmp.log to compare the files later on. The code that is written has to be added in log4j.xml file:
<appender name="CMP" class="org.jboss.logging.appender.RollingFileAppender">
<errorHandler class="org.jboss.logging.util.OnlyOnceErrorHandler"/>
<param name="File" value="${jboss.server.home.dir}/log/cmp.log"/>
<param name="Append" value="false"/>
<param name="MaxFileSize" value="500KB"/>
<param name="MaxBackupIndex" value="1"/>
<layout class="org.apache.log4j.PatternLayout">
<param name="ConversionPattern" value="%d %-5p [%c] %m%n"/>
</layout>
</appender>
<category name="org.jboss.ejb.plugins.cmp">
<priority value="DEBUG" />
<appender-ref ref="CMP"/>
</category>
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