Introdution

There is a common view, that the DTO (Data Transfer Object) is an anti-pattern, but CSMapper targets to dispel this prejudice.

If we imagine a standard JavaEE application, then, as a rule, it has a "Layered architecture" with an API on top (which is Presensation Layer), and JPA domain model at the bottom (which is Persistence Layer). Also we can say that API parameters depends on JPA Entity Model at most, and is a kind of its projection. So here is the dummy copy paste come from, which is the reason that makes DTO called ~~antipattern~~. But this copy paste problem can be very simply solved, which is what the CSMapper makes, and turn the DTO back into a very cool pattern.

We can divide the solution into three parts:

generate plane POJOs, based on JPA Entity model;
construct API parameters with those plane POJOs;
merge values from Entity to POJO and vice versa;

That's it!

There are usage examples below, which will help to make some details clearer.

Usage

All features, that CSMapper provides, can be used out of the box with well known Java technology stack, such as Spring and Hibernate. The configuration is very simple and takes about 15 minutes:

1. Generate JPA Entity based POJOs

The code generation process occurs during the project build. This is done using the Maven plugin:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-javadoc-plugin</artifactId>
            <executions>
                <execution>
                    <id>domaindto</id>
                    <phase>generate-sources</phase>
                    <goals>
                        <goal>javadoc</goal>
                    </goals>
                    <configuration>
                        <doclet>org.carlspring.beans.utils.doclet.DomainDtoDoclet</doclet>
                        <subpackages>org.carlspring.beans.mapper.examples.domain</subpackages>
                        <docletArtifacts>
                            <docletArtifact>
                                <groupId>org.carlspring.beans</groupId>
                                <artifactId>cs-mapper-utils</artifactId>
                                <version>1.0</version>
                            </docletArtifact>
                        </docletArtifacts>
                        <additionalparam>
                            -basepackage
                            org.carlspring.beans.mapper.examples.domain
                            -outputfolder
                            ${project.build.directory}/generated-sources
                            -prefexedproperties
                            id,name
                        </additionalparam>
                        <useStandardDocletOptions>false</useStandardDocletOptions>
                        <maxmemory>512</maxmemory>
                    </configuration>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>build-helper-maven-plugin</artifactId>
            <executions>
                <execution>
                    <id>add-source</id>
                    <phase>generate-sources</phase>
                    <goals>
                        <goal>add-source</goal>
                    </goals>
                    <configuration>
                        <sources>
                            <source>${project.build.directory}/generated-sources</source>
                        </sources>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Note that this configuration must be placed in module, that contains JPA Entities

We using the DomainDtoDoclet to get JPA Entities metadata from .java sources. Also there will be a dedicated cs-mapper-plugin instead of maven-javadoc-plugin and build-helper-maven-plugin in future versions.

2. BeanMapper instace configuration

BeanMapper can be easily configured inside Spring Application Context using BeanMapperFactoryBean like this:

@Configuration
public class AppConfiguration {

   ...

    @Bean
    public BeanMapperFactoryBean beanMapper(EntityManagerFactory emf)
    {
        BeanMapperFactoryBean result = new BeanMapperFactoryBean(emf);
        result.setMappedClasses(Arrays.asList(DomainDtoClasses.domainDtoClasses));
        result.setPackagesToScan("your.application.package.name.api.dto");
        return result;
    }
}

3. Merge POJOs with JPA Entities with BeanMapper

@Component
public class SampleApiService {

    @PersistenceContext
    private EntityManager entityManager;

    @Autowired
    private BeanMapper beanMapper;

    public PetStoreReadDto getPetStore(Long petStoreId) {
        PetStoreEntity petStoreEntity = entityManager.find(PetStoreEntity.class, petStoreId);  
        return (PetStoreReadDto) beanMapper.convertObject(petStoreEntity, PetStoreReadDto.class);
    }

}

Common Use Cases

Usage examples can be found here

sbespalov / cs-mapper