How to Get Singletons from @ Provides Method in Guice скачать в хорошем качестве

How to Get Singletons from @ Provides Method in Guice

Learn how to make use of `Singletons` in @ Provides method with Google Guice to maintain consistent instances across different executions. --- This video is based on the question https://stackoverflow.com/q/67482331/ asked by the user 'cheparsky' ( https://stackoverflow.com/u/11089623/ ) and on the answer https://stackoverflow.com/a/67583880/ provided by the user 'SQA' ( https://stackoverflow.com/u/11374458/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions. Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How can I get Singletons from @ Provides method? Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l... The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license. If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com. --- How to Get Singletons from @ Provides Method in Guice In the world of dependency injection and Java frameworks like Google Guice, managing instance lifecycles can be a challenge. One common issue arises when users try to employ the @ Provides annotation to manage instances of classes, particularly when they want to receive the same instance of a dependency across multiple operations. In this post, we will explore a practical example of this issue and guide you on how to effectively utilize Singletons with the @ Provides method. The Problem Consider a scenario where you have an environment module that utilizes a static @ Provides method to return different instances of a ProcessBuilder based on a product type. Here's a simplified version of the code structure: [[See Video to Reveal this Text or Code Snippet]] The challenge arises when the requirement is to get the same instance of ProcessBuilder when a certain product is selected multiple times. For instance, the goal is to achieve a consistent instance for Product1ProcessBuilder across multiple calls. Provided Structure You inject the ProcessBuilder using the Provider interface as seen in the Operation class: [[See Video to Reveal this Text or Code Snippet]] When executing tests as follows: Set CURRENT_PRODUCT = 'Product1' and call operate(), getting an instance of Product1ProcessBuilder. Change CURRENT_PRODUCT = 'Product2' and call operate(), getting an instance of Product2ProcessBuilder. Repeat the above steps, and the challenge persists: how to ensure that you receive the same instance for the same product after the initial call? The Solution To achieve the desired behavior of retrieving the same ProcessBuilder instance across multiple calls while still leveraging the @ Provides annotation, we need to make some adjustments to both the EnvironmentModule and the product builder classes. Step 1: Modify the @ Provides Method Instead of creating new instances of Product1ProcessBuilder and Product2ProcessBuilder directly, modify the @ Provides method to take these instances as parameters. When you register these instances in your Guice module, it will ensure that the same instance is returned for the same product: [[See Video to Reveal this Text or Code Snippet]] Step 2: Annotate Product Classes with @ Singleton It is also essential to annotate your product classes with @ Singleton. This ensures that each class is instantiated only once, which is crucial for maintaining state consistently across calls: [[See Video to Reveal this Text or Code Snippet]] Conclusion By restructuring the @ Provides method and appropriately using the @ Singleton annotation, you can ensure that you receive the same instance of ProcessBuilder each time you operate with the same product. This approach improves efficiency, reduces overhead, and maintains a consistent state across operations. Now you should be equipped with the necessary tools to handle Singletons in your Guice modules effectively. Happy coding!