Use of multiple DataSources in Spring Batch

You must provide your own BatchConfigurer. Spring does not want to make that decision for you

@Configuration
@EnableBatchProcessing
public class BatchConfig {

     @Bean
      BatchConfigurer configurer(@Qualifier("batchDataSource") DataSource dataSource){
        return new DefaultBatchConfigurer(dataSource);
      }

...

I would like to provide a solution here, which is very similar to the one answered by @vanarchi, but I managed to put all the necessary configurations into one class.

For the sake of completeness, the solution here assumes that primary datasource is hsql.

@Configuration
@EnableBatchProcessing
public class BatchConfiguration extends DefaultBatchConfigurer {

@Bean
@Primary
public DataSource batchDataSource() {

    // no need shutdown, EmbeddedDatabaseFactoryBean will take care of this
    EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder();
    EmbeddedDatabase embeddedDatabase = builder
            .addScript("classpath:org/springframework/batch/core/schema-drop-hsqldb.sql")
            .addScript("classpath:org/springframework/batch/core/schema-hsqldb.sql")
            .setType(EmbeddedDatabaseType.HSQL) //.H2 or .DERBY
            .build();
    return embeddedDatabase;
}

@Override
protected JobRepository createJobRepository() throws Exception {
    JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
    factory.setDataSource(batchDataSource());
    factory.setTransactionManager(transactionManager());
    factory.afterPropertiesSet();

    return (JobRepository) factory.getObject();
}

private ResourcelessTransactionManager transactionManager() {
    return new ResourcelessTransactionManager();
}

//NOTE: the code below is just to provide developer an easy way to access the in-momery hsql datasource, as we configured it to the primary datasource to store batch job related data. Default username : sa, password : ''
@PostConstruct
public void getDbManager(){
    DatabaseManagerSwing.main(
            new String[] { "--url", "jdbc:hsqldb:mem:testdb", "--user", "sa", "--password", ""});
}

}

THREE key points in this solution:

1. This class is annotated with @EnableBatchProcessing and @Configuration, as well as extended from DefaultBatchConfigurer. By doing this, we instruct spring-batch to use our customized batch configurer when AbstractBatchConfiguration tries to lookup BatchConfigurer;
2. Annotate batchDataSource bean as @Primary, which instruct spring-batch to use this datasource as its datasource of storing the 9 job related tables.
3. Override protected JobRepository createJobRepository() throws Exception method, which makes the jobRepository bean to use the primary datasource, as well as use a different transactionManager instance from the other datasource(s).

AbstractBatchConfiguration tries to lookup BatchConfigurer in container first, if it is not found then tries to create it itself - this is where IllegalStateException is thrown where there is more than one DataSource bean in container.

The approach to solving the problem is to prevent from creation the DefaultBatchConfigurer bean in AbstractBatchConfiguration. To do it we hint to create DefaultBatchConfigurer by Spring container using @Component annotation:

The configuration class where @EnableBatchProcessing is placed we can annotate with @ComponentScan that scan the package that contains the empty class that is derived from DefaultBatchConfigurer:

package batch_config;
...
@EnableBatchProcessing
@ComponentScan(basePackageClasses = MyBatchConfigurer.class)
public class MyBatchConfig {
    ...
}

the full code of that empty derived class is here:

package batch_config.components;
import org.springframework.batch.core.configuration.annotation.DefaultBatchConfigurer;
import org.springframework.stereotype.Component;
@Component
public class MyBatchConfigurer extends DefaultBatchConfigurer {
}

In this configuration the @Primary annotation works for DataSource bean as in the example below:

@Configuration
public class BatchTestDatabaseConfig {
    @Bean
    @Primary
    public DataSource dataSource()
    {
        return .........;
    }
}

This works for the Spring Batch version 3.0.3.RELEASE

The simplest solution to make @Primary annotation on DataSource work might be just adding @ComponentScan(basePackageClasses = DefaultBatchConfigurer.class) along with @EnableBatchProcessing annotation:

@Configuration
@EnableBatchProcessing
@ComponentScan(basePackageClasses = DefaultBatchConfigurer.class)
public class MyBatchConfig {