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How to configure multiple configurations of the same object graph using Guice?

How would you plot the object diagram shown in the diagram below?

The user object must combine information from two database databases.

Multiple configurations of the same object graph

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3 answers

I found a solution using private modules.

static class Service {
    @Inject Dao daoA;

    public void doSomething() {
        daoA.doA();
    }
}

static class Dao {
    @Inject DataSource dataSource;

    public void doA() {
        dataSource.execute();
    }
}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Connection {}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface X {}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Y {}

static class DataSource {
    @Connection @Inject String connection;

    public void execute() {
        System.out.println("execute on: " + connection);
    }
}

static class XServiceModule extends PrivateModule {
    @Override
    protected void configure() {
        bind(Service.class).annotatedWith(X.class).to(Service.class);
        expose(Service.class).annotatedWith(X.class);

        bindConstant().annotatedWith(Connection.class).to("http://server1");
    }
}

static class YServiceModule extends PrivateModule {
    @Override
    protected void configure() {
        bind(Service.class).annotatedWith(Y.class).to(Service.class);
        expose(Service.class).annotatedWith(Y.class);

        bindConstant().annotatedWith(Connection.class).to("http://server2");
    }
}

public static void main(String[] args) {
    Injector injector = Guice.createInjector(new XServiceModule(), new YServiceModule()); 

    Service serviceX = injector.getInstance(Key.get(Service.class, X.class));  
    serviceX.doSomething(); 

    Service serviceY = injector.getInstance(Key.get(Service.class, Y.class));
    serviceY.doSomething(); 
}
  • Different instances of the Service class can be identified using the annotations X and Y.
  • Hiding all other dependencies in the private module, there is no collision between Dao and DataSource
  • In two private modules, you can bind a constant in two different ways.
  • Services are displayed through disclosure.
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, assisted injection Guice factory, Service DataSource, , factory Service s.

0

You can use BindingAnnotations or just the generic @Named Annotation for this. I find that they are easiest to use with @ Provides-Methods:

@Provides
@Named("User1")
public SomeUser getUser(Service1 service) {
   return service.getUser();
}
@Provides
@Named("User2")
public SomeUser getUser(Service2 service) {
   return service.getUser();
}

and then:

@Inject
@Named("User1")
private SomeUser someuser;
...
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