Spring cloud task

Understanding Spring Cloud Task: A Guide with Examples

Spring Cloud Task is a microservices framework that enables developers to create and manage short-lived microservices, commonly known as tasks. Unlike typical long-running microservices, tasks are designed to execute a specific piece of logic, complete their work, and then terminate. This approach is especially useful for batch processing, ETL jobs, and other finite operations.

Key Concepts of Spring Cloud Task

1. Task Definition: A task in Spring Cloud Task is any application that completes its work and then ends. It could be a Spring Boot application that performs a database migration or a data processing job.
2. Task Execution: Each run of a task is considered a task execution. Spring Cloud Task provides detailed metadata about each execution, such as start time, end time, exit status, and more.
3. Integration with Spring Batch: Spring Cloud Task can integrate seamlessly with Spring Batch to handle complex batch processing jobs.

Setting Up Spring Cloud Task

Step 1: Add Dependencies

Create a new Spring Boot project using Spring Initializr (https://start.spring.io/). Include these necessary dependencies in your pom.xml

For Maven:

##language-xml

<!-- Spring cloud tasks -->
<dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-task</artifactId>
</dependency>
<!-- RAM H2 Database -->
<dependency>
   <groupId>com.h2database</groupId>
   <artifactId>h2</artifactId>
   <scope>runtime</scope>
</dependency>


Step 2: Create a Task Application

Create a simple Spring Boot application that performs a specific task. For this example, we will create a task that prints a message to the console.

##language-java

package com.example.demo;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.task.configuration.EnableTask;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
@EnableTask
public class DemoApplication {

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

 @Bean
 public CommandLineRunner commandLineRunner() {
   return args -> System.out.println("Hello, Spring Cloud Task!");
 }

}


In this example, the @EnableTask annotation enables Spring Cloud Task support, and the CommandLineRunner bean defines the task's logic.

Step 3: Configure Task Metadata Storage

Spring Cloud Task requires a data store to persist task execution metadata. You can configure a database like H2, MySQL, or PostgreSQL in your application.properties file.

For an in-memory H2 database:

##language-ini

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.datasource.platform=h2

spring.datasource.initialize=true


Step 4: Run the Task

Run your Spring Boot application. Each time the application starts and completes its work, it creates a new task execution entry in the metadata store.

##language-shell

mvn spring-boot:run


Code available here

Advanced Example: Integrating with Spring Batch

Spring Cloud Task can be used to run Spring Batch jobs. Here’s an example of how to integrate a Spring Batch job with Spring Cloud Task.

Step 1: Add Dependencies

Include the Spring Batch dependency along with Spring Cloud Task.

For Maven:

##language-xml

<dependency>
   <groupId>org.springframework.cloud</groupId>
   <artifactId>spring-cloud-starter-task</artifactId>
</dependency>
<dependency>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-batch</artifactId>
</dependency>


Step 2: Define a Batch Job

Create a simple batch job that processes data from a CSV file and writes it to the console.

##language-java

package com.example.demo;

import org.springframework.batch.core.Job;
import org.springframework.batch.core.JobParametersBuilder;
import org.springframework.batch.core.Step;
import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
import org.springframework.batch.core.job.builder.JobBuilder;
import org.springframework.batch.core.launch.JobLauncher;
import org.springframework.batch.core.repository.JobRepository;
import org.springframework.batch.core.step.builder.StepBuilder;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.task.configuration.EnableTask;
import org.springframework.context.annotation.Bean;
import org.springframework.core.env.Environment;
import org.springframework.transaction.PlatformTransactionManager;

@SpringBootApplication
@EnableTask
@EnableBatchProcessing
public class BatchTaskApplication {

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

@Bean
public Job job(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
Step step = new StepBuilder("step", jobRepository)
.<String, String>chunk(1, transactionManager)
.reader(() -> "Hello, Spring Batch!")
.writer(System.out::println)
.build();

return new JobBuilder("job", jobRepository)
.start(step)
.build();
}
}


Step 3: Configure Batch Metadata Storage

Spring Batch requires its own set of tables for metadata. Configure these in your application.properties.

##language-ini

spring.batch.initialize-schema=always


Since batch 5.0 some extra configuration is needed to automatically configure tables

See this stackoverflow for details

##language-java

@Configuration
@EnableConfigurationProperties(BatchProperties.class)
public class BatchConfig {
   @Bean
   @ConditionalOnMissingBean(BatchDataSourceScriptDatabaseInitializer.class)
   BatchDataSourceScriptDatabaseInitializer batchDataSourceInitializer(
DataSource dataSource,
@BatchDataSource ObjectProvider<DataSource> batchDataSource,
BatchProperties properties) {
           return new BatchDataSourceScriptDatabaseInitializer(
           batchDataSource.getIfAvailable(() -> dataSource),
               properties.getJdbc());
   }
}


Step 4: Running your job via the JobLauncher

There are a couple of ways you can run your job (a scheduler etc) but for simplicity we will run it from our CommandLineRunner so that it runs when the service starts as a proof of concept.

##language-java

   @Bean
   public CommandLineRunner commandLineRunner(JobLauncher jobLauncher, Job job, Environment environment) {
       return args -> {
           jobLauncher.run(job, new JobParametersBuilder()
                   .addLong("time", System.currentTimeMillis())
                   .toJobParameters());
       };
   }


Code available here

Conclusion

Spring Cloud Task is a powerful framework for managing short-lived microservices. By leveraging its integration with Spring Batch, developers can build robust, scalable solutions for processing finite tasks. Whether you are migrating data, processing files, or running batch jobs, Spring Cloud Task provides the necessary tools to streamline your workflow and ensure successful task execution.

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