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What does this PR do?

This PR implements the Rate Limiting Design Pattern in Java using three different strategies:

Token Bucket
Fixed Window
Adaptive Rate Limiter

It simulates concurrent client requests to multiple services (S3, DynamoDB, Lambda) and applies appropriate rate-limiting logic to manage request throughput, prevent system overload, and simulate elastic behavior under pressure.

Jun 01 '25 17:06 skamble2

PR Summary

This PR implements the Rate Limiting Design Pattern in Java using three different strategies: Token Bucket, Fixed Window, and Adaptive Rate Limiter. It simulates concurrent client requests to multiple services (S3, DynamoDB, Lambda) and applies appropriate rate-limiting logic to manage request throughput, prevent system overload, and simulate elastic behavior under pressure. The implementation includes comprehensive unit tests and diagrams.

Changes

File	Summary
`pom.xml`	Updated the parent pom.xml to include the `rate-limiting-pattern` module and fixed spacing.
`rate-limiting-pattern/README.md`	Added a comprehensive README file explaining the rate limiting pattern, including diagrams, code examples, and real-world applications.
`rate-limiting-pattern/etc/AdaptiveRateLimiter.png`	New file: Added a flowchart diagram for the Adaptive Rate Limiter strategy.
`rate-limiting-pattern/etc/FixedWindowRateLimiter.png`	New file: Added a flowchart diagram for the Fixed Window Rate Limiter strategy.
`rate-limiting-pattern/etc/TokenBucketRateLimiter.png`	New file: Added a flowchart diagram for the Token Bucket Rate Limiter strategy.
`rate-limiting-pattern/etc/UMLClassDiagram.png`	New file: Added a UML class diagram illustrating the relationships between classes in the rate limiting pattern.
`rate-limiting-pattern/pom.xml`	Added a pom.xml file for the `rate-limiting-pattern` module, defining dependencies and build configurations.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/AdaptiveRateLimiter.java`	Implemented the AdaptiveRateLimiter class, which dynamically adjusts the rate limit based on system health. It uses a TokenBucketRateLimiter internally and periodically adjusts the limit based on success or failure of requests.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/App.java`	Created a main application class to demonstrate the usage of the different rate limiter strategies with simulated concurrent client requests to multiple services.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/FindCustomerRequest.java`	Created a `FindCustomerRequest` class that implements `RateLimitOperation` to represent a rate-limited customer lookup operation.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/FixedWindowRateLimiter.java`	Implemented the FixedWindowRateLimiter class, which uses a simple counter within a fixed time window to limit the number of requests.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/RateLimitException.java`	New file: Created a base exception class for rate limiting errors.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/RateLimitOperation.java`	New file: Created an interface `RateLimitOperation` to represent a business operation that needs rate limiting.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/RateLimiter.java`	New file: Created an interface `RateLimiter` for different rate limiting strategies.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/ServiceUnavailableException.java`	New file: Created an exception class for when a service is temporarily unavailable.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/ThrottlingException.java`	New file: Created an exception class for when AWS-style throttling occurs.
`rate-limiting-pattern/src/main/java/com/iluwatar/rate/limiting/pattern/TokenBucketRateLimiter.java`	Implemented the TokenBucketRateLimiter class, which uses a token bucket algorithm to control the rate of requests.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/AdaptiveRateLimiterTest.java`	New file: Added unit tests for the AdaptiveRateLimiter class, verifying its behavior under different scenarios.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/AppTest.java`	New file: Added unit tests for the App class, covering different scenarios like successful requests, throttling, and service unavailability.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/AppTestUtils.java`	New file: Added utility methods for testing the App class.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/ConcurrencyTests.java`	New file: Added concurrency tests to verify the behavior of the rate limiters under concurrent requests.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/ExceptionTests.java`	New file: Added unit tests for the custom exception classes, verifying their functionality.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/FindCustomerRequestTest.java`	New file: Added unit tests for the FindCustomerRequest class, verifying its execution under different conditions.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/FixedWindowRateLimiterTest.java`	New file: Added unit tests for the FixedWindowRateLimiter class, verifying its behavior under different scenarios.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/RateLimitOperationTest.java`	New file: Added an interface for testing RateLimitOperation implementations.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/RateLimiterTest.java`	New file: Added an abstract class for testing RateLimiter implementations.
`rate-limiting-pattern/src/test/java/com/iluwatar/rate/limiting/pattern/TokenBucketRateLimiterTest.java`	New file: Added unit tests for the TokenBucketRateLimiter class, verifying its behavior under different scenarios.