SpringBootSamples.txt

		Date : 12/06/2020
		Spring Boot 9 AM 
		Mr. RAGHU
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			Spring Boot Scheduling
			----------------------
Scheduling: Executing task multiple time(in a loop)
            based on period of time or point of time.

period of time : It is a Time Gap
  4hrs,32 mins, 5 days, 6 months..etc

point of time : It is a exact date/time.
  11:00AM
  6th Jan
  12:45 PM ..etc

Ex:
a. Shop Sotfware -> Generate Report everyday by night 8PM.
b. Database backup after every 3 months.
c. CredCard Bill for every 30 days.
d. Bank Monthly Statements
e. Salary Slips
f. Every Month phone bill/Power Bill/...(Billings)
g. Stock Market Reports by 4PM
..etc


Q)What is demon thread in Java? 
A) _______________
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*)Spring Boot Scheduling Can be implemented using 3 different concepts. Given as

	a. fixedDelay **
	b. fixedRate
	c. cron expression ***

---Steps to implement Scheduling:---------------------------
i. Define one method with type public and void return type, that zero params
    (method called as Container as a Thread).

   public void  <anyName>(){
     //logic
   }

ii. Apply annotation : @Scheduled over method

iii. Write one annotation @EnableScheduling over starter class
--------------------------------------------------------------

a. fixedDelay ** :-
  This process is used to execte a task based on period of time(Time Gap only).
  Time value must be provided in mill sec(1000 mill sec = 1 sec)

--Example--
package in.nit.service;
import java.util.Date;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
@Component
public class MyReportService {

	@Scheduled(initialDelay = 5000,fixedDelay = 2000) //1000 mill sec=1 sec
	public void  showReport() {
		System.out.println("REPORT->"+new Date());
	}
	
}
-----------------------------------------------------------
Here initialDelay gives a time gap for Application startup and first method call.
fixedDelay: It gives exact time gap between last method execution complete to
             next method execution start.

Values must be given in mill sec only (1000 mill sec =1 sec)

Ex:  @Scheduled(fixedDelay = 1000 * 60 * 60 * 24 * 3)  //3days
Ex:  @Scheduled(fixedDelay = 1000 * 60 )  // 1 min

=>** @Scheduled is processed by ScheduledAnnotationBeanPostProcessor
================================================================
b. fixedRate :- It give max time gap between two method calls including wait time.

-Example-
package in.nit.service;
import java.util.Date;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class MyReportService {

	@Scheduled(initialDelay = 5000,fixedRate =  1000) 
	public void  showReport() {
		System.out.println("REPORT->"+new Date());
	}
	
}

*)Main method class:
package in.nit;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@SpringBootApplication
@EnableScheduling
public class SpringBoot2SchedulingExApplication {

	public static void main(String[] args) {
		SpringApplication.run(SpringBoot2SchedulingExApplication.class, args);
	}

}

---------**********----------------------------------------------------
https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/scheduling/support/CronSequenceGenerator.html
-------------------------------------------------------------------------
cron expression:- It is a concept of Unix/Linux OS. Used to schedule a Task.

=> cron expression by default point of time.

Cron Format is:
     SEC     MIN    HRS    DAY    MONTH    WEEKDAY
     0-59    0-59   0-23   1-31   1-12     SUN-MON

Possible Symbols:
   *   =  Any/All
   -   =  Range
   ,   =  Possible values
   /   =  Period of Time
   ?   =  Any/All used only for DAY/WEEK DAY when Month is provided.

--------Examples------------------------
#1.  0 0 9 * * *
=> Execute Given task every day- 9:00:00 AM

#2.  0  0  9  12  DEC  SUN-MON
=> Execute Given task every year DEC-12th (any week day)
   at 9:00:00 AM

#3.  0  0  9  12   *   *
=> Execute Given task every month 
   12th Day 9:00:00 AM 

#4.  0   0   16  *  *  *
=> Execute Given task every 4:00:00 PM

#5.  0  0  6,18  *  *  *
=> Execute Given task every 2 times
     6AM and 6PM

#6. 0  0  6-9  *  *  *
=> Execute Given task every 4 times
    6AM, 7AM, 8AM, 9AM

#7. 0  10  *   *  *  *
=>  Execute Given task every Hour 10th Min
      7:10:00 AM
      8:10:00 AM

#8. 10  *  *   *  *  *
=>  Execute Given task every minute 10th Sec
    3:45:10 PM
    3:46:10 PM

---------Time Gap-----------------------------
#9. */10   *  *  *  *  *
=>  Execute Given task every 10 Sec gap

#10.  0   0/10   9   *  *  *
=> Execute Given task every Day 
    9:00:00 AM

 and also gap of 10 mins
   9:10:00
   9:20:00
   9:30:00
   9:40:00
   9:50:00
   --over--

#11.  0  30/15   8,9  *  *  *

=>  Execute Given task every Day
     8:30:00
     9:30:00

     also gap of 15 min
     8:45:00
     9:00:00
     9:15:00
     9:45:00
    
#12   0  0  9  *  JAN  *
=> Invaild. When month is provided then you must give DAY and WEEK DAY
            ELSE to use ? to indicate all DAY and ALL WEEK DAYS
 
 => Vaild one : 0  0  9  ?  JAN  ?


#13  0  *  9  *  *  *
=> Invaild. 
  a. If we provide Hrs then must specify any number for Mins and Sec 
  b. If we provide Mins then must specify any number for  Sec 

 Vaild One : 0  0  9  *  * *
Invaild One: *  *  9  *  * *


Q) @Scheduled(cron = "* * * * * *") 
A) _______________.

Q) @Scheduled(cron = "* * * * *") 
A) _______________.


--Task-------------
1. Write Cron Expression for Happy New Year

2. Happy B'Day to my Dear ___