Quartz_Scheduler - Yash-777/LearnJava GitHub Wiki

Getting started with Quartz - GitHUB

Quartz Job Scheduler is Open Source for Job Automation by scheduling Time Interval. So that the job can be executed when ever the Trigger is fired. Trigger Listeners fires at a specified fire time. When ever trigger is raised, execute() method of the Specified class which implements JOB Interface will be invoked.

Use Cron Maker to Generate Corn Expression.

You need Quartz core library, named quartz-x.y.z.jar (where x.y.z is a version number), in its classpath.

Version_1.8.5

Example Main Class where the Scheduler Demon is Going to Start:

@Controller public class SchedulerFactoryTest {

	public static Scheduler schedulerDemon = null;
	static {
		try { //Using thread pool 'org.quartz.simpl.SimpleThreadPool' - with 20 threads.
			if(schedulerDemon == null){
				Properties p = new Properties();
				p.setProperty("org.quartz.threadPool.class", "org.quartz.simpl.SimpleThreadPool");
				p.setProperty("org.quartz.threadPool.threadCount", "20");
				StdSchedulerFactory factory = new StdSchedulerFactory(p);
				schedulerDemon = factory.getScheduler();
				schedulerDemon.start();
			}
		} catch (SchedulerException e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args) {
		HttpServletRequest request = null; HttpServletResponse response = null;
		ModelMap model = null;
		new SchedulerFactoryTest().Test(request, response, model);
	}
	
	@RequestMapping(value = "/ScheduleReq")
	public void Test(HttpServletRequest request,HttpServletResponse response, ModelMap model){
		String jobName = "Unique Name";
		SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		Date date = null;
		try {
			String startDate = "2017-1-10", startTime = "19:39:05";
			String dateInString = startDate + " " + startTime;
			date = formatter.parse(dateInString);
			System.out.println("Dtae Supplied : "+date);
		} catch (ParseException e) {
		}
		
		JobDetail job = new JobDetail();
		job.setName(jobName);
		job.setJobClass(Quartz_JOB_Impl.class);
		job.getJobDataMap().put("myKEY", jobName);
		
		SimpleTrigger trigger = new SimpleTrigger();
		trigger.setName(jobName);
		trigger.setStartTime(date);

		try {
			schedulerDemon.scheduleJob(job, trigger);
		} catch (SchedulerException e) {
			e.printStackTrace();
		}
	}
}

Class which implements JOB interface and @override execute(). so that the execute() method code will be executed by scheduler when trigger is raised.

public class Quartz_JOB_Impl implements Job {

	@Override
	public void execute(JobExecutionContext context) throws JobExecutionException {
		Date time = context.getFireTime();
		String jobName = (String)context.getJobDetail().getJobDataMap().get("myKEY");
		System.out.format("Trigger Time : %s, KEY : %s \n", time, jobName);
		try {
			System.out.println("Scheduler Demon Thread is Shutdown.");
			SchedulerFactoryTest.schedulerDemon.shutdown();
		} catch (SchedulerException e) {
			e.printStackTrace();
		}
	}
}

Version_2.1.5

When ever Records get changed in Data Base trigger fires event example.

Note: If you are facing compile time Problem regarding jar version, then exclude them in POM.

<properties>
	<hibernateVersion>3.1.2.RELEASE</hibernateVersion>
</properties>
<dependencies>
	<dependency>
		<groupId>org.hibernate</groupId>
		<artifactId>hibernate-validator</artifactId>
		<version>${hibernateVersion}</version>
		<!--
		<exclusions>
			<exclusion>
				<groupId>org.slf4j</groupId>
				<artifactId>slf4j-api</artifactId>
			</exclusion>
		</exclusions>
		-->
	</dependency>
</dependencies>

Quartz is the most well known solution to schedule processes in Java environments, but you have a lot of options list.

In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior.

Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y). An instance method in a subclass with the same signature and return type as an instance method in the super-class overrides the super-class's method.

Java OOP concepts
Class  - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance  (Reusability by placing common code in single class)
 1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
 * Is-A   Relation - Class A extends B
 * Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading    2. Runtime Overriding  [Greek - "many forms"]


int[] arr = {1,2,3}; int arrLength = arr.length;   // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.

List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]

// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
    private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
    public Employee(String name) { this.empName = name; }
}

Native Java Code for Hashtable.h, Hashtable.cpp SQL API.

You can check your current JDK and JRE versions on your command prompt respectively,

  • JDK javac -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/p: javac 1.8.0_121
  • JRE java -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/P: java version "1.8.0_102"

JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? C:\Softwares\OpenJDK\, 7-zip

Fatal error compiling: invalid target release: JRE and JDK must be of same version 1.8.0.XXX

Disable TLS 1.0 and 1.1security-libs/javax.net.ssl: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).

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