Understand Google Guice in 5 mins with picture`

Google Guice is light way DI framework, I recently worked on Spark, so can’t use spring framework, so I use Google Guice to replicate the spring DI, I will show both Spring config and Google Guice to compare both.

Following is the picture to display what I need:

Guice Class Diagram

So we design ETL tool, and ETL tool need Extractor to extrate data from either CSV file or database, and when we assemble our job, we need binding one of the extractor to the SampleJobRunner and then give to SparkETLApplication the main class to run.

Here is how Spring frame work will do:

@Configuration
@PropertySource("classpath:samplejob.yml")
@ConfigurationProperties
@Getter
@Setter
public class SampelJobConfig{

    @Bean(name="MySQLExtractor")
    public Extractor<SampleJobEvent> MySQLExtractor(){
        Extractor<SampleJobEvent> dbDataExtractor = new DBDataExtractor();
        return dbDataExtractor;
    }


    @Bean(name="SampleJobRunner")
    public JobRunner SampleJobRunner(JobConfig jobConfig, Loader<SampleJobEvent> sampleLoader, Extractor<SampleJobEvent> MySQLExtractor){
        JobRunner jobRunner = new JobRunner(jobConfig);
        Transformer<SampleJobEvent> transformer = new SampleTranformer();
        jobRunner.setLoader(sampleLoader);
        jobRunner.setExtractor(MySQLExtractor);
        jobRunner.setTransformer(transformer);

        return jobRunner;
    }
}

Basic of Basic - extends from `AbstractModule`

Here is how to do in Guice:

SampleJobConfig

public class SampelJobConfig extends AbstractModule{
      @Override
      protected void configure() {
            bind(Extractor.class).to(DBDataExtractor.class);
      }
}

JobRunner

@Getter
public class JobRunner<T> {

    private JobConfig jobConfig;
    private Extractor<T> extractor;
    private Loader<T> loader;
    private Transformer<T> transformer;

    @Inject
    public void setExtractor(Extractor extractor){
        this.extractor = extractor;
    }
    public JobRunner(JobConfig jobConfig){
        this.jobConfig = jobConfig;
    }

    public void run(T target){
        JobContext<T> jobContext = new JobContext<>();
        jobContext.setTarget(target);
        this.extractor.extract(jobContext);
        this.transformer.tranform(jobContext);
        this.loader.load(jobContext);
    }


}

SimpleSparkEtlJobApplication:

@Slf4j
public final class SimpleSparkEtlJobApplication {
    private SimpleSparkEtlJobApplication() {
        //disable construct
    }

    public static void main(String[] args) {
        //call jobRunner.run to start the process
        Injector injector = Guice.createInjector(new SampleJobConfig());
        JobRunner jobRunner = injector.getInstance(JobRunner.class);
        jobRunner.run();
    }

Implement Module Interface

extends from AbstractModule with bind command is not flexible, I want to have binding happen in SimpleSparkEtlApplication component:

Initial all the SampleJobConfig in the SimpleSparkEtlApplication
bind SampleJobConfig to the JobRunner.
Take care of the generic Type.

Provides vs Bind

If your instance can NOT be instantiate with bind, then you can use Provides annotation

    @Override
    protected void configure() {
        this.bind(Extractor.class).to(DBDataExtractor.class);
    }

Basic of Basic - extends from AbstractModule

Implement Module Interface

Provides vs Bind

Basic of Basic - extends from `AbstractModule`