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ClassNotFoundException vs NoClassDefFoundError

Both ClassNotFoundException and NoClassDefFoundError errors will be occurred  when the required Class not present in the Class path.
ClassNotFoundException is an Exception got arized when trying load class using
forName() method in class Class.
findSystemClass method in class ClassLoader .
loadClass method in class ClassLoader.

e.g. Class.forName("oracle.jdbc.driver.OracleDriver")
if the OracleDriver class file is not present in the Class path, then we will end up with this ClassNotFounException


NoClassDefFoundError is an Error thrown at Runtime, when the Class is present during the compile time and not present during Runtime of the Code, then we will end up with this NoClassDefFoundError.

1. When required Class is not available at Runtime available only in compile time.
2.Since NoClassDefFoundError error is an Subclass of LinkageError, it will occur when one of the     Dependent of the jar not present in class path.
3. When the Static initialization of Class failed then it triggers java.lang.ExceptionInInitializerError
 which also leads to this Error.

e.g.  Exception in thread "main" java.lang.NoClassDefFoundError


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Maven Build Life Cyles

Following are the maven build life cycles.

Clean - Removes the generated files in 'target' folder.

command : mvn clean

Validate - It validates your project and verify all the necessary information is there in project or not.

mvn  valiate

Compile - It compiles your project code.

mvn compile

Package - It takes the compiled code and packaged to JAR/WAR/EAR. It also compiles your code if your code is not compiled.

mvn package

Install -   It takes the packaged code and puts in your local maven repository (M2_HOME). It also does the compile and package if these are not already been done.

mvn install

Deploy - It takes the package and puts in remote repository for sharing accross team members or for other projects.

mvn deploy

FYI - Above commands can be used as variety of combinations.
e.g. mvn clean install
mvn clean package
mvn clean compile package install

To skip the tests to run 
mvn clean install -DskipTests

NO SQL Types and vendors in market


KEY - VALUE Store  - Similar to a  MAP.
   e.g. Dynamo DB or REDIS

DOCUMENT Sore  - Similar to KEY-VALUE, value can be JSON/XML and key will be unqiuely idnetified this document.
   e.g. Coutch DB or mongoDB.

Column Store - Multi timentional table, identifying data with row and column numbers.
  e.g.  Cassandra or Apache HBase

Graph Store - Store relation between nodes (record entities). It has better transaction management
e.g. Neo4J and Orient DB.