Q. What is Java?
Ans : Java is a programming language and computing platform.Java can be used to create complete applications that may run on a single computer or be distributed among servers and clients in a network. It can also be used to build a small application module or applet for use as part of a webpage.

Q. What are Java Servlets?
Ans : A servlet is a java program that executes on the server, accepting client requests and generating dynamic responses. Servlets do not just create HTML. Theses cal also be used to generate other MIME types, such as images.

Q. What is JSP (Java Server Pages)?
Ans : JSP are HTML documents that are interwoven with Java. JSP provides dynamic responses that is based on client request. JSP's are portable(write once, run everywhere). JSP's compile and run as servlets.

Q. What are EJBs (Enterprise Java Beans)? 
Ans :  EJBs are distributed components written in the java programming language.
EJBs provide distributable and deployable business services(Logic)to clients.
EJBs are reusable accross application servers.
EJBs execute within a container that provides management and control services.

Q. What is JDBC (Java Database Connectivity )?
Ans : Java Database Connectivity (JDBC) is an application programming interface (API) for the programming language Java, which defines how a client may access a database.
It is the standard java interface for accessing heterogeneous databases.

Q. What is JNDI (Java Naming and Directory Interface)?
Ans : JNDI is a Java API for a directory service that allows Java software clients to discover and look up data and objects via a name.It is an Java API for accessing naming and directory services.It built as a layer over DNS,LDAP and so on.

Q. What is JTA (Java Transaction API)?
Ans : JTA is a standard JAVA API that enables distributed transactions to be done across multiple X/Open XA resources in a Java environment.Java Transaction API (JTA) specifies standard Java interfaces between a transaction manager and the parties involved in a distributed transaction system: the resource manager, the application server, and the transactional applications.


Q. What is JMS (Java Messaging Service)?
Ans :  The Java Message Service is a Java API that allows applications to create, send, receive, and read messages.The JMS API defines a common set of interfaces and associated semantics that allow programs written in the Java programming language to communicate with other messaging implementations.The JMS API minimizes the set of concepts a programmer must learn in order to use messaging products but provides enough features to support sophisticated messaging applications.

Q. WHat is JAAS (Java Authentication & Autherization)?
Ans :  It is  a java based security management framework that supports single sign-on and a pluggable authentication Module(PAM).

Q. What is JMX (Java Management Extension)?
Ans : It defines a standard infrastructure to manage a device from java programs.MBEANS are the building blocks of JMX.

Q. What is JCA (Java Connector Architecture)?
Ans : JCA connects Enterprise Info. System(EIS) with resource adapters and resource adapters can be deployed in a Resource Adapter Archive(RAR).

Q. What is Client Application ?
Ans : The client application interacts with WLS through JRMP/T3, IIOP and jCOM.
The types of clients include :
a) Standalone java applications.
b) Applets within a browser.

Q. What is Web Client?
Ans : A web client interacts with oracle WLS via HTTP using servlets and JSPs.
The types of web clients includes :
a) Browser
b) Web Service(SOAP over HTTP)

Q. What is Proxy Server?
Ans : It forwards the requests to other machines. It can also be used to load balance a system.

Q. What is T3 protocol in WebLogic?
Ans :  T3 is an optimized protocol used to transport data between WLS and other java programs including clients and other WLS servers. WLS server keeps track of every JVM with which it connects and creates a single T3 connection to carry all traffic for a JVM.
T3 and T3s are proprietary protocols that are analogous to the industry standard HTTP or HTTPS protocols.

Some useful shortcut commands for windows

1: lusrmgr.msc-------to see user and computer

2: compmgmt.msc------to see computer management

3: devmgmt.msc-------to see devices and driver

4: ncpa.cpl----------to see local area connection

5: appwiz.cpl--------to see control pannel

6: control-----------to see control pannel

7: sysdm.cpl---------to see my computer properties

8: dnsmgmt.msc-------to see DNS configuration.

9: dsa.msc-----------to see Active Directory User and Computer.

10: intcpl.cpl-------to see internet properties.

11: cleanmgr---------to clean c drive from unwanted junk files.

12: taskmgr.msc------to open task manager

13: eventvwr.msc----to see event viewer

14: regedit.msc-----to check registry info.

15: gpedit.msc------to configure Group oplicy on local PC

16: services.msc----to check services information.

17: secpol.msc------to check local security and policy.

18: msconfig--------to check startup running application.

19: osk-------------ON SCREEN KEYBOARD

Configure ssmtp to use gmail SMTP relay on CentOS

1. Install ssmtp rpm as,

#yum install ssmtp

2. Now edit ssmtp.conf file as,

#vim /etc/ssmtp/ssmtp.conf

root=XXX@gmail.com
mailhub=smtp.gmail.com:465
AuthUser=XXXX@gmail.com
AuthPass=<Password of gmail account>
FromLineOverride=YES
UseTLS=YES
TLS_CA_File=/etc/pki/tls/certs/ca-bundle.crt

3. After this, make ssmtp default mta as,

#alternatives --config mta

it will ask to choose mta, here select the ssmtp and enter.


4. Now send the mail as,

#mail -s "SUBJECT" xxxxx@abc.com

javax.net.ssl.SSLKeyException in Node Manager status

Problem : Could not start node manager

Problem Explanation : I have changed my machine(It got currupted) and use the existing HDD partition to again run the machine. All was right but node manager was not running.

Error : javax.net.ssl.SSLKeyException

Solution : This issue has two solutions as,

A. Disable the hostname verification
B. Recreate the certificates

A. Disable the hostname verification ,

1. In the Admin console for your domain, go to Environment -> Servers -> AdminServer.
2. Click on the SSL tab.
3. Expand the “Advanced” section at the bottom.
4. Set Hostname Verification to None.
5. Save and activate the changes.



B. Recreate the certificates ,

1. First of all set the WLS enviornment varibales using,

$MIDDLEWARE_HOME/wlserver_10.3/server/bin/.setWLSEnv.sh

2. Backup the Demoidentity.jks keystore located in,

$MIDDLEWARE_HOME/wlserver_10.3/server/lib/DemoIdentity.jks

3. Generate the private key of the keystore using the following command:

java utils.CertGen -cn hostname -keyfilepass DemoIdentityPassPhrase -certfile newcert -keyfile newkey

Note : Here I got error "utils.CertGen not found"
Solution : For this we have need to set CLASSPATH manually as,

$export CLASSPATH=$CLASSPATH:/stage/oracle/middleware/wlserver_10.3/server/lib/weblogic.jar

After this run the above command again.

4. Import the generated key in the Demoidentity.jks using the following command:

java utils.ImportPrivateKey -keystore DemoIdentity.jks -storepass DemoIdentityKeyStorePassPhrase -keyfile newkey.pem -keyfilepass DemoIdentityPassPhrase -certfile newcert.pem -alias demoidentity.

5. Now restart the WebLogic Server.

To increase the heap size of a Managed server

1. Open Admin console, go to server-->server name-->Configuration-->server start.
2. Here in Arguments section, write the desired heap size as,

-Xms512m -Xmx512m

BEA-090087 - Server failed to bind to the configured Admin port. The port may already be used by another process.

BEA-090087 - Server failed to bind to the configured Admin port. The port may already be used by another process.

 Reason 1 : This error occured when we try to start managed server on other physical machine with node manager.


Solution : We have to create new node manager that points to other physical machine.

Procedure :

1. Go to Enviournment-->Machines.
2. Here click on New button, then give the name for the machine and select the type of the machine and then Next.
3.Here give the listen address and listen port of the node manager and click on Finish.

Reason 2 : This error occurred when we try to start two nodemanager on one physical machine. e.g. one for weblogic and second for OHS.

Solution : 

Just change the port of one nodemanager.

java.lang.OutOfMemoryError: PermGen space

Error : java.lang.OutOfMemoryError: PermGen space

Solution : Have to increase PermSize of weblogic server

Procedure :

Weblogic Version : 10.3.6

1. go to $DOMAIN_HOME/bin

2. Here edit the file setDomainEnv.sh.

$vim setDomainEnv.sh

3. Here change the value of min and max PerSize as,

241 MEM_PERM_SIZE_64BIT="-XX:PermSize=512m"
242 export MEM_PERM_SIZE_64BIT
243
244 MEM_PERM_SIZE_32BIT="-XX:PermSize=48m"
245 export MEM_PERM_SIZE_32BIT
246
247 if [ "${JAVA_USE_64BIT}" = "true" ] ; then
248         MEM_PERM_SIZE="${MEM_PERM_SIZE_64BIT}"
249         export MEM_PERM_SIZE
250 else
251         MEM_PERM_SIZE="${MEM_PERM_SIZE_32BIT}"
252         export MEM_PERM_SIZE
253 fi
254
255 MEM_MAX_PERM_SIZE_64BIT="-XX:MaxPermSize=1024m"
256 export MEM_MAX_PERM_SIZE_64BIT
257
258 MEM_MAX_PERM_SIZE_32BIT="-XX:MaxPermSize=128m"


Line no. 241 for Min. PermSize and Line no. 255 for Max. PerSize.