[FIXED] Spring : how to map Page<Entity> to Page<Object>

Issue

I have a Repositoy (StockRepository ) class which extends from JpaRepository. When calling the method findAll(Pageable pageable); the return result is Page<Stock>.

Now I want to convert the Page<Stock> to Page<StockDto>. But the compiler give the error below. How can I correct this Compile error ?

import org.springframework.core.convert.converter.Converter;
...
    public Page<StockDto> getAllStocksPageable(int pageNumber, int pageSize) {
    
        Pageable pageable = PageRequest.of(pageNumber, pageSize);
        Page<Stock> stocks = stockRepository.findAll(pageable);
    
        Page<StockDto> dtoPage = stocks.map(new Converter<Stock, StockDto>() {
            @Override
            public StockDto convert(Stock entity) {
                StockDto stockDto = new StockDto();
                ...
                return stockDto;
            }
    
        });
    
        return null;
    
    }

@Entity
@Table(name = "stock")
public class Stock {
        ....
}


// Pojo
public class StockDto {
    ....
 }


@Repository
public interface StockRepository extends JpaRepository<Stock, Integer> {
    ....
}

Solution

The error is pretty clear: Page.map() accepts a Function, but you've given it a Converter. Replace new Converter( with new Function( and convert( with apply( and it'll compile:

Page<StockDto> dtoPage = stocks.map(new Function<Stock, StockDto>() {
    @Override
    public StockDto apply(Stock entity) {
        StockDto stockDto = new StockDto();
        ...
        return stockDto;
    }
});

Better yet, use a lambda:

Page<StockDto> dtoPage = stocks.map(entity -> {
        StockDto stockDto = new StockDto();
        ...
        return stockDto;
    });

Answered By - Jelaby
Answer Checked By - Timothy Miller (JavaFixing Admin)