Toilet paper #106

Before I get stuck, I’d rather use MapStruct


An unpopular and error-prone task, which is recurring especially in multi-layered architectures, is the writing of mapper classes for similar objects, e.g. between database entities and request / response DTOs. Writing unit tests for such mappers is also cumbersome.


The Java library MapStruct ( takes on this task by generating mapping code automatically, based on annotations.


  • Generation at compile time: no influence on performance
  • Generated code uses getter / setter methods, so it's type safe, easy to debug and to understand / extend
  • Reasonable default conventions, behavior can easily be overwritten


Two complementary classes (getter / setter methods not shown):

public class CupOfCoffee {
    private Enums.Brand brand;
    private double temperature;
    private int volume;
    private double milk;
    private double sugar;
    private boolean isCorretto;
public class CupOfCoffeeDTO {
    private String brand;
    private String temperature;
    private int volumeOfCup;
    private double milk;
    private double sugar;
    private boolean isCorretto;

MapStruct base class:

@Mapper(componentModel = "spring")
public abstract class CoffeeMapper {
    @Mapping(source = "volume", target = "volumeOfCup")
    @Mapping(source = "temperature", target="temperature", numberFormat = "$#.0")
    public abstract CupOfCoffeeDTO toCupOfCoffeeDTO(CupOfCoffee entity);

    public abstract CupOfCoffee toCupOfCoffee(CupOfCoffeeDTO dto);

While compiling, MapStruct generates the mapping code according to the annotations. The explicit @Mapping annotations are only needed for non-trivial mappings (such as different variable names, number formats, etc.). The abstract class can still be extended by explicit mapping functions.


  • You have to recompile after each change of the abstract mapper class
  • Sometimes does not work very well with Lombok (another annotation-based code generator)
Toilet paper #106: MapStruct

Cookie Settings

This website uses cookies to personalize content and ads, provide social media features, and analyze website traffic. In addition, information about your use of the website is shared with social media, advertising, and analytics partners. These partners may merge the information with other data that you have provided to them or that they have collected from you using the services.

For more information, please refer to our privacy policy. There you can also change your cookie settings later on.

contact icon

Contact us now