How to return HashMap from Spring Repository

A Spring Data Repository typically returns entities or List of Object arrays List<Object[]> – for custom queries, not collections like HashMap<K, V> directly. You can structure a custom query or a method that returns a Map in your Service or in additional method, but it’s not automatic — you have to be explicit about it.

Example: Custom Repository Method Returning a Map

Let’s say you have an entity:

@Entity
public class Product {
    @Id
    private Long id;
    private String name;
    private Double price;
    // getters and setters
}

If you want to return a Map<String, Double> (e.g., product name to price), you can write a custom query like this:

Option 1: Use @Query and Stream it

public interface ProductRepository extends JpaRepository<Product, Long> {

    @Query("SELECT p.name, p.price FROM Product p")
    List<Object[]> findNameAndPricePairs();
    
    default Map<String, Double> getNamePriceMap() {
        return findNameAndPricePairs()
            .stream()
            .collect(Collectors.toMap(
                row -> (String) row[0],
                row -> (Double) row[1]
            ));
    }
}

Option 2: Use a custom DTO and convert manually

public interface ProductRepository extends JpaRepository<Product, Long> {

    @Query("SELECT new com.example.NamePriceDTO(p.name, p.price) FROM Product p")
    List<NamePriceDTO> findAllNamePrice();
}

Then convert that list into a map in service layer:

Map<String, Double> namePriceMap = repository.findAllNamePrice()
    .stream()
    .collect(Collectors.toMap(NamePriceDTO::getName, NamePriceDTO::getPrice));

TL;DR

No, Spring Data Repository doesn’t directly return HashMap<K, V>, but you can:

• Use @Query to extract pairs,
• Convert to Map<K, V> manually in the repo default method or in the service layer.