Simple Program using shedlock

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Simple Shedlock Code

pom.xml

	<dependency>
			<groupId>net.javacrumbs.shedlock</groupId>
			<artifactId>shedlock-spring</artifactId>
			<version>5.13.0</version>
		</dependency>
		<dependency>
			<groupId>net.javacrumbs.shedlock</groupId>
			<artifactId>shedlock-provider-jdbc-template</artifactId>
			<version>5.13.0</version>
		</dependency>

ShedLockConfig.java

import net.javacrumbs.shedlock.core.LockProvider;
import net.javacrumbs.shedlock.provider.jdbctemplate.JdbcTemplateLockProvider;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.jdbc.core.JdbcTemplate;

import javax.sql.DataSource;

@Configuration
public class ShedLockConfig {

    @Bean
    public LockProvider lockProvider(DataSource dataSource) {
        return new JdbcTemplateLockProvider(
                JdbcTemplateLockProvider.Configuration.builder()
                        .withJdbcTemplate(new JdbcTemplate(dataSource))
                        .withTableName("empmgmt.shedlock")
                        .build()

        );
    }
}

ShedlockDemoApplication.java

import net.javacrumbs.shedlock.spring.annotation.EnableSchedulerLock;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableScheduling;

@SpringBootApplication
@EnableScheduling
@EnableSchedulerLock(defaultLockAtMostFor = "PT4M")
public class ShedlockDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(ShedlockDemoApplication.class, args);
    }
}

PostFetchScheduler.java
fetchPosts method is called every minute

@Component
class PostFetchScheduler {

    final PostFetchService postFetchService;

    PostFetchScheduler(PostFetchService postFetchService) {
        this.postFetchService = postFetchService;
    }

    @Scheduled(cron = "0 */1 * ? * *")
    @SchedulerLock(name = "fetchPosts", lockAtMostFor = "PT2M", lockAtLeastFor = "PT1M")
    void fetchPosts() {
        postFetchService.fetchPosts();
    }
}

How to run the code

  1. Shedlock table should be created manually in database 
      CREATE TABLE shedlock (
    name VARCHAR(64) NOT NULL,         -- lock name
    lock_until TIMESTAMP NOT NULL,     -- time until lock is valid
    locked_at TIMESTAMP NOT NULL,      -- time when lock was acquired
    locked_by VARCHAR(255) NOT NULL,   -- identifier of the node that holds the lock
    PRIMARY KEY (name)
);
  2. Start multiple instance by supplying server.port and instance name as parameter
  3. First instance would create table in DB for posts for code in repo

Output

FAQ
Why we are defining lock timing at 2 places? 

@EnableSchedulerLock(defaultLockAtMostFor = "PT4M")

vs

  @SchedulerLock(name = "fetchPosts", lockAtMostFor = "PT2M", lockAtLeastFor = "PT1M")

@EnableSchedulerLock sets defaults for all tasks. A fallback setting for all tasks.

@SchedulerLock gives per-task overrides with more precise control. Fine-grained control, overriding the default for specific jobs.

Repo Link

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