Spring Boot Iterator Pattern Example: Hashing Service

This project demonstrates the Iterator Design Pattern in a Spring Boot application.
The application receives a text input via REST API and returns the hash values generated by multiple algorithms (MD5, SHA-1, SHA-224, SHA-256, SHA-384, SHA-512).

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🚀 API Example

Request:

curl --location 'http://localhost:8080/hash' \
--header 'Content-Type: application/json' \
--data '{
  "text": "hello"
}'

Response:

[
  {
    "algorithm": "MD5",
    "hash": "5d41402abc4b2a76b9719d911017c592"
  },
  {
    "algorithm": "SHA-1",
    "hash": "aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d"
  },
  {
    "algorithm": "SHA-224",
    "hash": "ea09ae9cc6768c50fcee903ed054556e5bfc8347907f12598aa24193"
  },
  {
    "algorithm": "SHA-256",
    "hash": "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
  },
  {
    "algorithm": "SHA-384",
    "hash": "59e1748777448c69de6b800d7a33bbfb9ff1b463e44354c3553bcdb9c666fa90125a3c79f90397bdf5f6a13de828684f"
  },
  {
    "algorithm": "SHA-512",
    "hash": "9b71d224bd62f3785d96d46ad3ea3d73319bfbc2890caadae2dff72519673ca72323c3d99ba5c11d7c7acc6e14b8c5da0c4663475c2e5c3adef46f73bcdec043"
  }
]

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🛠️ Project Structure

• HashIteration – Interface for all hash algorithm implementations.
• MD5HashIteration, SHA256HashIteration, etc. – Concrete classes implementing different algorithms.
• HashIterator – Central iterator class that loops through all HashIteration implementations.
• HashService – Calls HashIterator and prepares the response.
• HashController – REST API endpoint.

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🔑 Key Class: HashIterator

@Component
@RequiredArgsConstructor
public class HashIterator {

  private final List<HashIteration> hashIterations;

  public Map<HashType, String> hash(String text) {
    Map<HashType, String> result = new EnumMap<>(HashType.class);

    for (HashIteration hashIteration : hashIterations) {
      result.put(hashIteration.getHashType(), hashIteration.hash(text));
    }

    return result;
  }

}

Why is it important?

The HashIterator class embodies the Iterator Pattern by:

• Hiding the internal structure of the collection (List).
• Providing sequential access to all elements (hash algorithms).
• Returning results in a unified and extensible way.

Adding a new algorithm only requires:

1. Implementing HashIteration interface.
2. Registering the new class as a Spring component.

The HashIterator automatically includes it.

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⚙️ Run the Project

1. Clone this repository:

git clone https://github.com/ercansormaz/iterator-pattern.git

2. Navigate to the project folder and build:

mvn clean install

3. Run the application:

mvn spring-boot:run

4. Access the APIs at:

http://localhost:8080/hash

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📖 Design Pattern Insight

This project demonstrates how the Iterator Pattern can be applied in real-world scenarios where multiple strategies or processors need to be executed sequentially. Instead of exposing the internal list of algorithms, HashIterator provides a clean abstraction.

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📚 Further Reading

You can read a detailed explanation of this project and the Iterator Pattern in the blog post here:
👉 Read the Blog Post

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🤝 Contributing

Contributions are welcome! Feel free to fork the repo, submit pull requests or open issues.

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📜 License

This project is licensed under the MIT License.