DZone
Thanks for visiting DZone today,
Edit Profile
  • Manage Email Subscriptions
  • How to Post to DZone
  • Article Submission Guidelines
Sign Out View Profile
  • Post an Article
  • Manage My Drafts
Over 2 million developers have joined DZone.
Log In / Join
Refcards Trend Reports Events Over 2 million developers have joined DZone. Join Today! Thanks for visiting DZone today,
Edit Profile Manage Email Subscriptions Moderation Admin Console How to Post to DZone Article Submission Guidelines
View Profile
Sign Out
Refcards
Trend Reports
Events
Zones
Culture and Methodologies Agile Career Development Methodologies Team Management
Data Engineering AI/ML Big Data Data Databases IoT
Software Design and Architecture Cloud Architecture Containers Integration Microservices Performance Security
Coding Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
Partner Zones AWS Cloud
by AWS Developer Relations
Culture and Methodologies
Agile Career Development Methodologies Team Management
Data Engineering
AI/ML Big Data Data Databases IoT
Software Design and Architecture
Cloud Architecture Containers Integration Microservices Performance Security
Coding
Frameworks Java JavaScript Languages Tools
Testing, Deployment, and Maintenance
Deployment DevOps and CI/CD Maintenance Monitoring and Observability Testing, Tools, and Frameworks
Partner Zones
AWS Cloud
by AWS Developer Relations
Building Scalable Real-Time Apps with AstraDB and Vaadin
Register Now

Trending

  • Unlocking the Power of AIOps: Enhancing DevOps With Intelligent Automation for Optimized IT Operations
  • Mastering Time Series Analysis: Techniques, Models, and Strategies
  • Microservices With Apache Camel and Quarkus
  • Exploratory Testing Tutorial: A Comprehensive Guide With Examples and Best Practices

Trending

  • Unlocking the Power of AIOps: Enhancing DevOps With Intelligent Automation for Optimized IT Operations
  • Mastering Time Series Analysis: Techniques, Models, and Strategies
  • Microservices With Apache Camel and Quarkus
  • Exploratory Testing Tutorial: A Comprehensive Guide With Examples and Best Practices

Disambiguating Between Instances With Google Guice

Biju Kunjummen user avatar by
Biju Kunjummen
·
Feb. 11, 15 · Interview
Like (4)
Save
Tweet
Share
5.65K Views

Join the DZone community and get the full member experience.

Join For Free

Google guice provides a neat way to select a target implementation if there are multiple implementations of an interface. My samples are based on anexcellent article by Josh Long(@starbuxman) on a similar mechanism that Spring provides.

So, consider an interface called MarketPlace having two implementations, an AndroidMarketPlace and AppleMarketPlace:

interface MarketPlace {
}

class AppleMarketPlace implements MarketPlace {

    @Override
    public String toString() {
        return "apple";
    }
}

class GoogleMarketPlace implements MarketPlace {

    @Override
    public String toString() {
        return "android";
    }
}

and consider a user of these implementations:

class MarketPlaceUser {
    private final MarketPlace marketPlace;
    
    public MarketPlaceUser(MarketPlace marketPlace) {
        System.out.println("MarketPlaceUser constructor called..");
        this.marketPlace = marketPlace;
    }

    public String showMarketPlace() {
        return this.marketPlace.toString();
    }

}

A good way for MarketPlaceUser to disambiguate between these implementations is to use a guice feature called Binding Annotations. To make use of this feature, start by defining annotations for each of these implementations this way:

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

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

and inform the Guice binder about these annotations and the appropriate implementation corresponding to the annotation:

class MultipleInstancesModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(MarketPlace.class).annotatedWith(Ios.class).to(AppleMarketPlace.class).in(Scopes.SINGLETON);
        bind(MarketPlace.class).annotatedWith(Android.class).to(GoogleMarketPlace.class).in(Scopes.SINGLETON);
        bind(MarketPlaceUser.class).in(Scopes.SINGLETON);
    }
}

Now, if MarketPlaceUser needs to use one or the other implementation, this is how the dependency can be injected in:

import com.google.inject.*;

class MarketPlaceUser {
    private final MarketPlace marketPlace;

    @Inject
    public MarketPlaceUser(@Ios MarketPlace marketPlace) {
        this.marketPlace = marketPlace;
    }

}

This is very intuitive. If you have concerns about defining so many annotations, another approach could be to use @Named built-in Google Guice annotation, this way:

class MultipleInstancesModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(MarketPlace.class).annotatedWith(Names.named("ios")).to(AppleMarketPlace.class).in(Scopes.SINGLETON);
        bind(MarketPlace.class).annotatedWith(Names.named("android")).to(GoogleMarketPlace.class).in(Scopes.SINGLETON);
        bind(MarketPlaceUser.class).in(Scopes.SINGLETON);
    }
}

and use it this way, where the dependency is required:

import com.google.inject.*;

class MarketPlaceUser {
    private final MarketPlace marketPlace;

    @Inject
    public MarketPlaceUser(@Named("ios") MarketPlace marketPlace) {
        this.marketPlace = marketPlace;
    }

}
If you are interested in exploring this further, here is the Google guice sample and an equivalent sample using Spring framework
Google Guice Google (verb)

Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

Trending

  • Unlocking the Power of AIOps: Enhancing DevOps With Intelligent Automation for Optimized IT Operations
  • Mastering Time Series Analysis: Techniques, Models, and Strategies
  • Microservices With Apache Camel and Quarkus
  • Exploratory Testing Tutorial: A Comprehensive Guide With Examples and Best Practices

Comments

Partner Resources

X

ABOUT US

  • About DZone
  • Send feedback
  • Careers
  • Sitemap

ADVERTISE

  • Advertise with DZone

CONTRIBUTE ON DZONE

  • Article Submission Guidelines
  • Become a Contributor
  • Visit the Writers' Zone

LEGAL

  • Terms of Service
  • Privacy Policy

CONTACT US

  • 600 Park Offices Drive
  • Suite 300
  • Durham, NC 27709
  • support@dzone.com

Let's be friends: