The Idempotentizer is a Java library designed to simplify the process of implementing idempotent behavior in your consumer applications. Idempotence is a crucial concept in distributed systems and APIs, ensuring that repeated requests have the same effect as the initial request, even if the request is executed multiple times.

To get started with Idempotentizer in your Java project, follow these simple steps:

1. Add Idempotentizer to Your Project: Include Idempotentizer as a dependency in your project. You can either download the JAR file manually or use a dependency management tool like Maven or Gradle.

   <!-- Maven -->
   <dependency>
       <groupId>com.ersalgado</groupId>
       <artifactId>idempotentizer</artifactId>
       <version>1.0.0</version>
   </dependency>

   // Gradle
   implementation 'com.ersalgado:idempotentizer:1.0.0'

2. Create an instance: Create an instance of Idempotentizer, providing one of the available repository implementations.

   // Create an instance of one of the provided repositories.
   Repository repository = new SQLRepository(datasource, new JacksonObjectSerde());
   
   // Instances of Idempotentizer are thread safe so you can
   // use this instance as a singleton in your application.
   Idempotentizer idempotentizer = new DefaultIdempotentizer(repository);

3. Handle Idempotent Requests: Use Idempotentizer to check if incoming requests were already processed, ensuring that duplicate requests are detected and processed accordingly.

   private void doUpdateInventoryOnce(UpdateInventoryRequest request, UUID idempotencyKey) {
       var requestInfo = idempotentizer.checkProcessed(idempotencyKey, CONSUMER_ID);
       if (!requestInfo.getProcessed()) {
   
           // Process the request...
   
           // Mark the request as processed.
           idempotentizer.markAsProcessed(idempotencyKey, CONSUMER_ID);
       } else {
           log.debug("The request '{}' for consumer '{}' was already processed", idempotencyKey, CONSUMER_ID);
       }
   }

   You can store any result object generated after successfully processing a request to ensure consistency for all subsequent duplicate requests. This stored result can then be returned when duplicate calls are detected, maintaining the integrity of the system.

   private MyResult doUpdateInventoryOnce(UpdateInventoryRequest request, UUID idempotencyKey) {
       var requestInfo = idempotentizer.checkProcessed(idempotencyKey, CONSUMER_ID);
       if (!requestInfo.getProcessed()) {
           var result = // Process the request and get a result...
   
           // Mark the request as processed, providing a result.
           idempotentizer.markAsProcessed(idempotencyKey, CONSUMER_ID, result);
           
           return result;
       } else {
           log.debug("The request '{}' for consumer '{}' was already processed", idempotencyKey, CONSUMER_ID);
           return (MyResult) requestInfo.getReturnedValue();
       }
   }

Contributions to Idempotentizer are welcome! If you encounter any issues, have ideas for improvements, or would like to contribute code, please submit a pull request or open an issue.

The Idempotentizer library is open-source software licensed under the MIT License.