how to create multiple instance of same type using google Guice

Question

We have used Google Guice framework for dependency injection. I need to create multiple insatnce of an interface in java.

The execution starts from here: KfhRecordValidator.java class in the below code:

public class KfhRecordValidator implements RequestHandler<Request, Response> {
       public Response handleRequest(Request request, Context context) 
        {
     // Resolve the necessary dependencies, and process the request.
       Injector injector = Guice.createInjector(new 
                      DependencyModule());
            Processor processor = 
                 injector.getInstance(Processor.class);
              return processor.process(request, context);
}}

The process class is having reference of RecordValidationHelper class and the injection is through constructor. IRecordValidationService.java is an interface that is having validate method.

public interface IRecordValidationService {
              void validate(Record record) throws ValidationException;}

class processor is having one method called process that is being called in RecordValidationHelper class.

class Processor {
   private final RecordValidationHelper recordValidationHelper;
@Inject
@SuppressWarnings({"WeakerAccess"})
public Processor(IRecordValidationService recordValidationService, 
IRecordService<ErrorRecord> recordService,
                 S3UtilsInterface s3Utils, IEnvironmentVariableReader 
                 environmentVariableReader) {
                 this.recordValidationHelper = new 
                 RecordValidationHelper(recordValidationService);
                 this.errorRecordHelper = new 
                 ErrorRecordHelper(recordService, environmentVariableReader);
}

public Response process(Request request, @SuppressWarnings("unused") Context context) {

    // Validate records
    List<LambdaRecord> records = recordValidationHelper.processRecords(request.getRecords());}

Class DependencyModule.java extneds AbstractModule class of Guice injection that is having configure method.

class DependencyModule extends AbstractModule {
@Override
protected void configure() {
    String validationType = System.getenv("ValidationType");

    validationType= validationType.toLowerCase(Locale.ENGLISH);

    String valType[]= validationType.split(",");
    int length= valType.length;

    for(int i=0;i<length;i++){

        switch(valType[i]){
         case "json":
             bind(IRecordValidationService.class).to(JsonValidationService.class);
             break;
         case "avro":
             bind(IRecordValidationService.class).to(AvroSchemaValidationService.class);
             break;
         case "clientlogging":
             bind(IRecordValidationService.class).to(ClientLoggingValidationService.class);
             break;
         case "servicelogs":
             bind(IRecordValidationService.class).to(ServiceLoggingValidationService.class);
             break;
         default:
             throw new UnsupportedOperationException(String.format("Encountered an unsupported ValidationType of '%s'.", valType[i]));
        }

    } } }

SO the issue is if I am getting validation type as AVRO, JSON then it will bind IRecordValidationService to respective JsonValidationService/AvroSchemaValidationService class. I need to create multiple instance for that but it supports only once instance at a time. Below is the RecordValidationHelper.java class

public class RecordValidationHelper extends AbstractModule { private final IRecordValidationService recordValidationService;

@Inject
public RecordValidationHelper(IRecordValidationService recordValidationService) {
    this.recordValidationService = recordValidationService;
}

public List processRecords(List requestRecords) { List records = new ArrayList<>();

    for (RequestRecord record : requestRecords) {
        try {

            Record domainRecord = new Record();
            domainRecord.setKey(record.getRecordId());
            domainRecord.setValue(new String(Base64.getDecoder().decode(record.getData())));

            // Use the injected logic to validate the record.
            ((IRecordValidationService) 
           recordValidationService).validate(domainRecord);}
           catch (ValidationException ex) {}}}
           return records;}

Anyone having any idea about how it should be implemented to get multiple instance suitable for this.

Answer 1

Use @Named bindings

In your DependencyModule , bind using names:

bind(IRecordValidationService.class)
  .annotatedWith(Names.named("json"))
  .to(JsonValidationService.class);
bind(IRecordValidationService.class)
  .annotatedWith(Names.named("avro"))
  .to(AvroSchemaValidationService.class);
bind(IRecordValidationService.class)
  .annotatedWith(Names.named("clientlogging"))
  .to(ClientLoggingValidationService.class);
bind(IRecordValidationService.class)
  .annotatedWith(Names.named("servicelogs"))
  .to(ServiceLoggingValidationService.class);

Then in your injectee:

@Inject
public RecordValidationHelper(
    @Named("json") IRecordValidationService jsonValidation,
    @Named("avro") IRecordValidationService avroValidation,
    @Named("clientlogging") IRecordValidationService clientLoggingValidation,
    @Named("servicelogs") IRecordValidationService serviceLogsValidation,
  ) {
    this.jsonValidation = jsonValidation;
    this.avroValidation = avroValidation;
    this.clientLoggingValidation = clientLoggingValidation;
    this.serviceLogsValidation = serviceLogsValidation;
}

See Guice's BindingAnnotation wiki page for more info.