DDevelopment & Design

MapStruct mapper injection in OSGi Blueprint

What is MapStruct?According to MapStruct website: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 metho…

What is MapStruct?

According to MapStruct website:

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.

Inject MapStruct mapper in Blueprint OSGi

Such mappings are sometimes necessary in our integration projects. We also use OSGi to create our applications and Blueprint for dependency injection. Blueprin Maven Plugin makes it very easy to use, providing annotation support.

MapStruct supports component models like cdi, spring and jsr330, so generated classes could be used as beans. Fortunately, Blueprint Maven Plugin uses annotations from JSR 330, such as Singleton or Named.

The only thing we have to do is to add property componentModel with value jsr330 to a mapping interface:

@Mapper(componentModel = "jsr330")
public interface PersonMapper {
    Person toDomain(PersonDto personDto);
}

and now we can inject PersonMapper to our beans:

@Singleton
@AllArgsConstructor
public class CreatePersonHandler {
    private final PersonRepository personRepository;
    private final PersonMapper personMapper;

    // ...
}

Blueprint Maven Plugin will generate an XML file with bean PersonMapperImpl and inject it to CreatePersonHandler:

<?xml version="1.0" encoding="UTF-8"?><blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
    <bean id="createPersonHandler" class="com.github.alien11689.osgi.mapstructblueprint.CreatePersonHandler">
        <argument ref="personRepository"/>
        <argument ref="personMapperImpl"/>
    </bean>
    <bean id="personMapperImpl" class="com.github.alien11689.osgi.mapstructblueprint.PersonMapperImpl"/>
    <bean id="personRepository" class="com.github.alien11689.osgi.mapstructblueprint.PersonRepository"/>
</blueprint>

Generate all mappers with JSR 330 annotations

If you have multiple mappers and all of them should be beans, then you can simply add one compiler argument in configuration and all the mappers will have @Singleton and @Named annotations by default.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    ...
    <build>
        <plugins>
            ...
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <compilerArgs>
                        <compilerArg>
                             -Amapstruct.defaultComponentModel=jsr330
                        </compilerArg>
                    </compilerArgs>
                </configuration>
            </plugin>
            ...
        </plugins>
    </build>
</project>

Try it on your own

The code is available at Github.

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DDevelopment & Design

Simple trick to DRY your Grails controller

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

  1. wrap everything with a simple withStoppingOnRender method,
  2. whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}