Java bean mappings, the easy way!

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What is it?

MapStruct is a code generator that greatly simplifies the implementation of mappings between Java bean types based on a convention over configuration approach.

The generated mapping code uses plain method invocations and thus is fast, type-safe and easy to understand.

Why?

Multi-layered applications often require to map between different object models (e.g. entities and DTOs). Writing such mapping code is a tedious and error-prone task. MapStruct aims at simplifying this work by automating it as much as possible.

In contrast to other mapping frameworks MapStruct generates bean mappings at compile-time which ensures a high performance, allows for fast developer feedback and thorough error checking.

How?

MapStruct is an annotation processor which is plugged into the Java compiler and can be used in command-line builds (Maven, Gradle etc.) as well as from within your preferred IDE.

MapStruct uses sensible defaults but steps out of your way when it comes to configuring or implementing special behavior.


Latest News

MapStruct Spring Extensions 1.1.1 released

It is my pleasure to announce the next official release of MapStruct Spring Extensions. What started out as a StackOverflow question turned into its own (sub-)project within the MapStruct organization.

Changes in this release:

  • This release is functionally identical to 1.1.0. The only modification worthwhile mentioning is a fix to the dependencies for the newly introduced test-extensions module which now won’t rely on outdated Spring versions anymore. Thanks to George Noble for pointing out this oversight which led to some organizations rejecting the library due to a security vulnerability in the respective Spring versions.

Including the annotations and extensions defined in this project will generate a class acting as bridge between MapStruct’s conventions and Spring' s ConversionService API that in turn can be added to any Mapper’s uses attribute. See the examples for details.

Read more...

Support for accessing property names, passing annotations to generated code, sponsoring MapStruct and much more: MapStruct 1.6.0.Beta1 is out

It’s my pleasure to announce the first Beta release of MapStruct 1.6.

The new release comes with a lot of new functionality, e.g.:

  • Access to target / source property names in conditional and mapping methods
  • Passing annotations to generated code
  • Add javadoc to generated code
  • New built-in conversions

With this release we are also happy to announce that MapStruct has started accepting donations through Open Collective or GitHub. We’d like to thank to everyone that has already started in supporting us:

Read more...

MapStruct Spring Extensions 1.1.0 released

It is my pleasure to announce the next official release of MapStruct Spring Extensions. What started out as a StackOverflow question turned into its own (sub-)project within the MapStruct organization.

Changes in this release:

  • New module test-extensions which contains a @ConverterScan annotation that greatly simplifies the writing of integration tests. Thanks to Joose Haverinen for the suggestion.
  • New annotation @AdapterMethodName which allows a developer to override the default name for generated adapter methods. Thanks to pw-lehre for the inspiration.
  • New annotation @DelegatingConverter that will generate a converter calling the one whose method is annotated with this. The intended use is in conjunction with MapStruct Core’s @InheritInverseConfiguration. Thanks again to pw-lehre for the idea.

Including the annotations and extensions defined in this project will generate a class acting as bridge between MapStruct’s conventions and Spring' s ConversionService API that in turn can be added to any Mapper’s uses attribute. See the examples for details.

Read more...

MapStruct in 2 Minutes

The following shows how to map two objects using MapStruct.

Let's assume we have a class representing cars (e.g. a JPA entity) and an accompanying data transfer object (DTO).

Both types are rather similar, only the seat count attributes have different names and the type attribute is of a special enum type in the Car class but is a plain string in the DTO.

  • public class Car {
    
        private String make;
        private int numberOfSeats;
        private CarType type;
    
        //constructor, getters, setters etc.
    }
  • public class CarDto {
    
        private String make;
        private int seatCount;
        private String type;
    
        //constructor, getters, setters etc.
    }

The mapper interface

To generate a mapper for creating a CarDto object out of a Car object, a mapper interface needs to be defined:

    1. @Mapper 1
    2. public interface CarMapper {
    3.  
    4. CarMapper INSTANCE = Mappers.getMapper( CarMapper.class ); 3
    5.  
    6. @Mapping(source = "numberOfSeats", target = "seatCount")
    7. CarDto carToCarDto(Car car); 2
    8. }

The @Mapper annotation 1 marks the interface as mapping interface and lets the MapStruct processor kick in during compilation.

The actual mapping method 2 expects the source object as parameter and returns the target object. Its name can be freely chosen.

For attributes with different names in source and target object, the @Mapping annotation can be used to configure the names.

Where required and possible a type conversion will be executed for attributes with different types in source and target, e.g. the type attribute will be converted from the enumeration type into a string.

Of course there can be multiple mapping methods in one interface, for all of which an implementation will be generated by MapStruct.

An instance of the interface implementation can be retrieved from the Mappers class. By convention, the interface declares a member INSTANCE 3, providing clients access to the mapper implementation.

Using the mapper

Based on the mapper interface, clients can perform object mappings in a very easy and type-safe manner:

  • @Test
    public void shouldMapCarToDto() {
        //given
        Car car = new Car( "Morris", 5, CarType.SEDAN );
    
        //when
        CarDto carDto = CarMapper.INSTANCE.carToCarDto( car );
    
        //then
        assertThat( carDto ).isNotNull();
        assertThat( carDto.getMake() ).isEqualTo( "Morris" );
        assertThat( carDto.getSeatCount() ).isEqualTo( 5 );
        assertThat( carDto.getType() ).isEqualTo( "SEDAN" );
    }

Tell me more!

You like what you see? Then check out the reference documentation to learn how to get started with MapStruct and which advanced features there are. In case you need help or want to propose a new feature just drop by on the GitHub Discussions.

You want to contribute to the development of MapStruct? That's great, this page has all the information you need.