Spring Batch Tutorial Part #6

Spring Batch: JobRepository and JobExplorer

Spring Batch provides a robust framework for batch processing. Two essential components for managing job executions and
retrieving job-related data are JobRepository and JobExplorer.

JobRepository

Overview

JobRepository is the central component in Spring Batch responsible for persisting batch job metadata. It stores
details about job executions, step executions, and job instances in a database.

Responsibilities

• Persisting job and step execution metadata.
• Tracking job execution status and history.
• Storing job parameters and context.
• Managing job restarts and recoveries.

Configuration

To configure JobRepository, you need a DataSource and a BatchConfigurer:

@Configuration
@EnableBatchProcessing
public class BatchConfig {

    @Bean
    public JobRepository jobRepository(DataSource dataSource, PlatformTransactionManager transactionManager)
            throws Exception {
        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(dataSource);
        factory.setTransactionManager(transactionManager);
        factory.setDatabaseType("POSTGRES"); // Change according to your database
        return factory.getObject();
    }
}

JobExplorer

Overview

JobExplorer is a read-only version of JobRepository, allowing access to job execution data without modifying it. It
is useful for querying batch job history and monitoring running jobs.

Responsibilities

• Fetching job instances and job executions.
• Querying step executions.
• Retrieving execution parameters.

Configuration

To configure JobExplorer, you can use the JobExplorerFactoryBean:

@Bean
public JobExplorer jobExplorer(DataSource dataSource) throws Exception {
    JobExplorerFactoryBean factory = new JobExplorerFactoryBean();
    factory.setDataSource(dataSource);
    return factory.getObject();
}

Usage Example

You can use JobExplorer to fetch job execution details:

@Autowired
private JobExplorer jobExplorer;

public void getJobDetails() {
    List<JobInstance> jobInstances = jobExplorer.getJobInstances("myJob", 0, 10);
    for (JobInstance instance : jobInstances) {
        List<JobExecution> executions = jobExplorer.getJobExecutions(instance);
        executions.forEach(execution -> System.out.println("Job Execution ID: " + execution.getId()));
    }
}

Differences Between JobRepository and JobExplorer

Feature	JobRepository	JobExplorer
Read-Write	Yes	No
Tracks Job Execution	Yes	Yes
Manages Restarts	Yes	No
Query Job History	No	Yes

Conclusion

• Use JobRepository when you need to persist and manage job executions.
• Use JobExplorer when you need to query job history and execution status without modifying the data.
• Both are crucial for building scalable and maintainable Spring Batch applications.