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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.

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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

Regular Expression in java

1[abc]a, b, or c (simple class)
2[^abc]Any character except a, b, or c (negation)
3[a-zA-Z]a through z or A through Z, inclusive (range)
4[a-d[m-p]]a through d, or m through p: [a-dm-p] (union)
5[a-z&&[def]]d, e, or f (intersection)
6[a-z&&[^bc]]a through z, except for b and c: [ad-z] (subtraction)
7[a-z&&[^m-p]]a through z, and not m through p: [a-lq-z](subtraction)

X?  X, once or not at all
X*  X, zero or more times
X+  X, one or more times
X{n}    X, exactly n times
X{n,}   X, at least n times
X{n,m}  X, at least n but not more than m times

Reluctant quantifiers
X?? X, once or not at all
X*? X, zero or more times
X+? X, one or more times
X{n}?   X, exactly n times
X{n,}?  X, at least n times
X{n,m}? X, at least n but not more than m times

Possessive quantifiers
X?+ X, once or not at all
X*+ X, zero or more times
X++ X, one or more times
X{n}+   X, exactly n times
X{n,}+  X, at least n times
X{n,m}+ X, at least n but not more than m times

To Split the String…

Most Common mistakes in Java Coding.

1. Copy & Paste

Its one of the most powerful tool and technique in the typical programmer. But at the same time its too dangerous that you ought to forgot the code according to you requirements. So always be cautious about what piece of code you are copying. Read at least two to three times to avoid the tricky for fishy things while your unit testing.

2. Exception Catch Block.

Always give priority to write some thing useful and meaning full statements in the exception catch block.It really worth when you troubling shooting the issues. Never leave this block with empty or sop's. And always throw the exception to the calling method.

3. String operations

Since String is immutable object, when you do any operation on string that results a new object. So after you do any modifications on String and do assign the string some object and use it.

4. Null pointers

Don't perform the operations on objects without checking the Object null condition. And while checking the null condition alw…

CRON Expressions

CRON expression.Cron-Expressions are used to configure instances of CronTrigger. Cron-Expressions are strings that are actually made up of seven sub-expressions, that describe individual details of the schedule. These sub-expression are separated with white-space, and represent:

SecondsMinutesHoursDay-of-MonthMonthDay-of-WeekYear (optional field)+-------------------- second (0-59)|+----------------- minute (0-59)||+-------------- hour (0-23)|||+----------- day of month (1-31)||||+-------- month (1-12)|||||+----- day of week (0-6)(Sunday=0 or 7)||||||+-- year [optional]|||||||******* command to be executed Examples.1. For every 10 seconds 0/10 * * 1/1 * ?2. For every Sunday midnight at 23:00 0 0 23 ? * SUNSome of the frequently used schedulesYou can play with website for more number of combinations. Cron Expression ExamplesCron Expre

Programming Guide Lines

1. Modularization

Do not write the whole logic code in one block/function instead delegate the each and individual responsibility to each function. For example if you are converting one Date time format to another write this logic in Utils and use it. It might be useful in other place as well.

And if you come across any common piece which is repeated in you logic put it in a function call where ever needed. This is basic fundamental rule.

2.Single Responsibility.

Always delegate single responsibility to one block/function of code. Don't mess multiple operations in a single block/function. And make sure block/function of name should ideally match to what it actually does.

3. Name Justification

Always declare the class, method or variable names based on its purpose. And don't use any shorter names.
The one who reads your code should get idea what actually it does.