CDI factory design pattern with properties file

Question

I have a interface like this :

@Singleton
public interface StorageEngine {
    String upload(InputStream inputStream);

    InputStream download(String fileName);

    int size(String fileName);

    boolean delete(String fileName);
}

and multiple implementation :

public class LocalFileSystemEngine implements StorageEngine {
   // Implement methods ...
}

public class DropboxEngine implements StorageEngine {
   // Implement methods ...
}

public class GoogleDriveEngine implements StorageEngine {
   // Implement methods ...
}

and this Producer class :

import jakarta.enterprise.context.ApplicationScoped;
import jakarta.enterprise.inject.Any;
import jakarta.enterprise.inject.Instance;
import jakarta.enterprise.inject.Produces;
import jakarta.inject.Inject;
import org.eclipse.microprofile.config.inject.ConfigProperty;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

@ApplicationScoped
public class StorageProducer {
    private static final Logger logger = LoggerFactory.getLogger(StorageProducer.class);

    @Inject
    @ConfigProperty(name = "storage.engine-type",defaultValue = "local-filesystem")
    private String engineType;

    @Inject
    @Any
    private Instance<StorageEngine> storageEngineInstance;

    @Produces
    public StorageEngine getStorageEngine() {
        // How to implement ???
    }
}

my goal is :
read engine type from microprofile properties file and produce storage engine .
Is there any way to inject StorageEngine without qualifier annotation ?

I need to have only this on injection point class:

@MultipartConfig
@WebServlet(urlPatterns = "/file")
public class FileServlet extends HttpServlet {
     @Inject
    private StorageEngine storageEngine;    
    

    // Implement service method 
}

anyone can help me ?

Laird Nelson · Accepted Answer · 2023-09-28 21:38:27Z

2

All of the solutions are too complicated. Qualifiers are not needed.

Restrict the bean types of the concrete implementations and then have your producer method pick the right one:

@Typed(LocalFileSystemEngine.class) // <-- NOTE
public class LocalFileSystemEngine implements StorageEngine {
   // Implement methods ...
}

@Typed(DropboxEngine.class) // <-- NOTE
public class DropboxEngine implements StorageEngine {
   // Implement methods ...
}

@Typed(GoogleDriveEngine.class) // <-- NOTE
public class GoogleDriveEngine implements StorageEngine {
   // Implement methods ...
}

@Produces
public StorageEngine getStorageEngine(@ConfigProperty(name = "storage.engine-type",
                                                      defaultValue = "local-filesystem")
                                      String type,
                                      LocalFilesystemEngine lfe,
                                      DropboxEngine de,
                                      GoogleDriveEngine gde) {
  return switch (type) {
    case "local-filesystem" -> lfe;
    case "google-drive" -> gde;
    case "dropbox" -> de;
    default -> throw new CreationException();
  };
}

answered Sep 28, 2023 at 21:38

Laird Nelson

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1 Comment

mah454 Over a year ago

Wowww , Great answer , Thank you .

Benjamin Confino · Accepted Answer · 2023-09-28 14:18:17Z

0

The idiomatic way to do it would be to use qualifiers, but to use them inside getStorageEngine().

@Produces
public StorageEngine getStorageEngine() {

    if (engineType.equals("type one")) {
        //TypeOne.class is a qualifier
        storageEngineInstance.select(TypeOne.class);
    } else if //repeat for all engine types
}

If you really do not want to use qualifiers, Instance is also iterable

@Produces
public StorageEngine getStorageEngine() {

    if (StorageEngine storageEngine : storageEngineInstance) {
       if (storageEngine.someValue().equals(engineType.someValue())) {
           return storageEngine;
       }
    } 
}

answered Sep 28, 2023 at 14:18

Benjamin Confino

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1 Comment

mah454 Over a year ago

I do this , but does not work on liberty application server : WELD-001409: Ambiguous dependencies for type StorageEngine with qualifiers @Default

mah454 · Accepted Answer · 2023-09-28 14:32:22Z

I finally found a good solution .
Actually we still need @Qualifier annotation .

first create a annotation like this :

@Qualifier
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface StorageType {
    String value();
}

now create annotation literal for that :

public class StorageTypeLiteral extends AnnotationLiteral<StorageType> implements StorageType {

    private final String value;

    public StorageTypeLiteral(String value) {
        this.value = value;
    }

    @Override
    public String value() {
        return value;
    }
}

Change implementations :

@StorageType("local-filesystem")
public class LocalFileSystemEngine implements StorageEngine {
   // Implement methods ...
}

@StorageType("Dropbox")
public class DropboxEngine implements StorageEngine {
   // Implement methods ...
}

@StorageType("GoogleDrive")
public class GoogleDriveEngine implements StorageEngine {
   // Implement methods ...
}

now update producer class like this :

@ApplicationScoped
public class StorageProducer {
    private static final Logger logger = LoggerFactory.getLogger(StorageProducer.class);

    @Inject
    @ConfigProperty(name = "storage.engine-type",defaultValue = "local-filesystem")
    private String engineType;

    @Inject
    @Any
    private Instance<StorageEngine> storageEngineInstance;

    @Produces
    public StorageEngine getStorageEngine() {
        Instance<StorageEngine> instance = storageEngineInstance.select(new StorageTypeLiteral(engineType));
        if (!instance.isResolvable())
            throw new IllegalArgumentException("Storage %s not implemented yet".formatted(engineType));
        return instance.get();
    }
}

It's work .
Thank you .

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