Spring is well-organized architecture consisting  of seven modules. Modules in the Spring framework are:

Spring AOP
One of the key components of Spring is the AOP framework. AOP is used in Spring:

To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on Spring’s transaction abstraction.
To allow users to implement custom aspects, complementing their use of OOP with AOP
Spring ORM
The ORM package is related to the database access. It provides integration layers for popular object-relational mapping APIs, including JDO, Hibernate and iBatis.

Spring Web
The Spring Web module is part of Spring?s web application development stack, which includes Spring MVC.

Spring DAO
The DAO (Data Access Object) support in Spring is primarily for standardizing the data access work using the technologies like JDBC, Hibernate or JDO.

Spring Context
This package builds on the beans package to add support for message sources and for the Observer design pattern, and the ability for application objects to obtain resources using a consistent API.

Spring Web MVC
This is the Module which provides the MVC implementations for the web applications.

Spring Core
The Core package is the most import component of the Spring Framework.
This component provides the Dependency Injection features. The BeanFactory  provides a factory pattern which separates the dependencies like initialization, creation and access of the objects from your actual program logic.

Static keyword in java

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start by creating a Spring Security configuration class that extends WebSecurityConfigurerAdapter. By adding @EnableWebSecurity, we get Spring Security and MVC integration support.

Reference: https://developer.okta.com/blog/2018/10/05/build-a-spring-boot-app-with-user-authentication

3. How to cancel an order for user-specific settings at the spring level? 

3b. Multi calls between ms to ms? 


4. Tomcat Max Threads settings in Springboot application? 

server.tomcat.max-connections	8192	Maximum number of connections that the server accepts and processes at any given time. Once the limit has been reached, the operating system may still accept connections based on the "acceptCount" property.
server.tomcat.max-http-form-post-size	2MB	Maximum size of the form content in any HTTP post request.
server.tomcat.max-swallow-size	2MB	Maximum amount of request body to swallow.
server.tomcat.max-threads	200	Maximum amount of worker threads.
server.tomcat.mbeanregistry.enabled	false	Whether Tomcat's MBean Registry should be enabled.
server.tomcat.min-spare-threads	10	Minimum amount of worker threads.
server.tomcat.port-header	X-Forwarded-Port	Name of the HTTP header used to override the original port value.
server.tomcat.processor-cache	200	Maximum number of idle processors that will be retained in the cache and reused with a subsequent request. When set to -1 the cache will be unlimited with a theoretical maximum size equal to the maximum number of connections.
server.tomcat.protocol-header		Header that holds the incoming protocol, usually named "X-Forwarded-Proto".

Reference :
https://docs.spring.io/spring-boot/docs/current/reference/html/appendix-application-properties.html

5. Sort Employee salary using Java Streams and display salary which is greater than X amount? Java 8 - streams, lambda expression



Reference :
https://www.java2novice.com/java-8/streams/filter-method-example/

6. When do we use java inner classes?
It is a way of logically grouping classes that are only used in one place: If a class is useful to only one other class, then it is logical to embed it in that class and keep the two together. Nesting such "helper classes" makes their package more streamlined.


Use a non-static nested class (or inner class) if you require access to an enclosing instance's non-public fields and methods. Use a static nested class if you don't require this access.



Inner classes are used to get functionality that can get an object better than method.
They can be used in the case when a set of multiple operations are required and chances of reusability are good inside the class and they will not be accessed but methods outside the outer class.
Inner classes are made to achieve multiple inheritances also.
Inner classes are used when they are useful in the class context.
They are used to separate logic inside classes.
inner class means one class which is a member of another class. There are basically four types of inner classes in java.

1) Nested Inner class

2) Method Local inner classes

3) Anonymous inner classes

4) Static nested classes

7. Spring boot - Dependency injection types? 

There are basically three types of dependency injection:
constructor injection: the dependencies are provided through a class constructor.
setter injection: the client exposes a setter method that the injector uses to inject the dependency.
interface injection: the dependency provides an injector method that will inject the dependency into any client passed to it. Clients must implement an interface that exposes a setter method that accepts the dependency.
So now its the dependency injection’s responsibility to:

• Create the objects
• Know which classes require those objects
• And provide them all those objects

Reference : https://java2blog.com/introduction-to-spring-framework/#Spring_Boot

8 . Mutable(Changable) Vs Immutable(Not Changable) ? 

Mutable object – You can change the states and fields after the object is created

Sting is im-mutable , Stringbuffer is mutable and Date is mutable  .


How to create a Mutable class?
To create a mutable class in Java you have to make sure the following requirements are satisfied:

• Provide a method to modify the field values
• Getter and Setter method

How to create an Immutable class?
A class should be declared as final so that it can’t be extended.
All the fields should be made private so that direct access is not allowed
No setter methods
Make all mutable fields final, so that they can be assigned only once.

9.

 JBOSS start and stop shell scripts - domain mode - host controller - domain controller
===========START DOMAIN CONTROLLER MACHINE JBOSS=================
echo "Setting JBOSS Env"
export JAVA_HOME=/opt/app/java/jdk/jdk160
export PATH=$PATH:/opt/app/jboss/jboss-eap-6.3/bin:$JAVA_HOME/bin
echo "PATH is : $PATH"

echo "JBOSS Environment is ready and starting jboss in domain mode"
echo "MY:JAVA_OPTS: $JAVA_OPTS"
export JAVA_OPTS="$JAVA_OPTS -DASOCPropsFile=/abc/etc/abc.props -DLNSPropsFile=/pns/etc/pns.props -DAVSPropsFile=/bvs/etc/bvs.props -DEOTPropsFile=/toe/etc/toe.props -DLPSPropsFile=/psl/etc/psl.props -DADLPropsFile=/hfl/etc/hfl.props -Dcom.sun.xml.ws.transport.http.client.HttpTransportPipe.dump=true"
echo "MY AFTER:JAVA_OPTS: $JAVA_OPTS"

/export/opt/jboss/jboss-eap-6.3/bin/domain.sh -b cldv0015.abc.cpf.com -bmanagement cldv0015.abc.cpf.com &
=============================================
============START HOST CONTROLLER==========
=============================================

==========STOP JBOSS Process harshly==============
echo "Stopping JBOSS JAVA processes"

for i in `ps -eaf | grep jboss | grep java | cut -d " " -f6`
{
        kill -9 $i
    echo "Killing: $i"
}
ps -eaf | grep jboss | grep java
echo "Stop completed"
============================================