Griffon JPA Plugin

1. Introduction

The JPA plugin enables lightweight access multiple SQL databases. This plugin does NOT provide domain classes nor dynamic finders like GORM does.

Griffon version: 2.12.0

2. Usage

The following sections describe how you may use this plugin in a project.

2.1. Configuration

You must create a configuration file named Jpa that holds the settings for creating instances of EntityManager. This file follows the same standard configuration mechanism as the application’s Config file, which means you can define the configuration using

a properties file
a Java file
a Groovy script

The following example shows the default settings needed to connect the default database taking into account that each environment may connect to a different database.

src/main/resources/Jpa.groovy

persistenceUnit {
    factory {

    }
    entitiyManager {

    }
}

environments {
    development {
    }
    test {
    }
    production {
    }
}

You may configure multiple named persistence units (the default unit is aptly named default) as the following snippet shows

src/main/resources/Jpa.groovy

persistenceUnits {
    internal {
    }
    people {
    }
}

Don’t forget to add META-INF/persistence.xml to your project.

The following properties are optional

Property Type Default Description

Property	Type	Default	Description
connect_on_startup	boolean	false	Establishes a connection to the database at the beginning of the `Startup` phase.

connect_on_startup

boolean

false

Establishes a connection to the database at the beginning of the Startup phase.

The plugin’s module registers a EntityManagerHandler helper class that defines the base contract for accessing a database and issue SQL queries to it. This class has the following methods

griffon.plugins.jpa.EntityManagerHandler.java

@Nullable
<R> R withEntityManager(@Nonnull EntityManagerCallback<R> callback);

@Nullable
<R> R withEntityManager(@Nonnull String persistenceUnitName, @Nonnull EntityManagerCallback<R> callback);

void closeEntityManager();

void closeEntityManager(@Nonnull String persistenceUnitName);

These method are aware of multiple persistence units. If no persistenceUnitName is specified when calling them then the default persistence unit will be selected. You can inject an instance of this class anywhere it’s needed using @Inject. There is one callback you may use with this method: EntityManagerCallback.

This callback is defined using a functional interface approach, which means you can apply lambda expressions if running with JDK8+ or closures if running Groovy.

griffon.plugins.jpa.EntityManagerCallback.java

public interface EntityManagerCallback<R> {
    R handle(@Nonnull String persistenceUnitName, @Nonnull EntityManager entityManager);
}

2.1.1. Bootstrap

You may execute arbitrary database calls during connection and disconnection from a EntityManager. Simply create a class that implements the JpaBootstrap interface and register it within a module, for example

src/main/java/com/acme/SampleJpaBootstrap.java

package com.acme;

import javax.persistence.EntityManager;

import javax.annotation.Nonnull;
import javax.inject.Named;

@Named("sample")
public class SampleJpaBootstrap implements JpaBootstrap {
    @Override
    public void init(@Nonnull String persistenceUnitName, @Nonnull EntityManager entityManager) {
        // operations after first connection to database
    }

    @Override
    public void destroy(@Nonnull String persistenceUnitName, @Nonnull EntityManager entityManager) {
        // operations before disconnecting from the database
    }
}

src/main/java/com/acme/ApplicationModule.java

package com.acme;

import griffon.plugins.jpa.JpaBootstrap;
import griffon.core.injection.Module;
import org.codehaus.griffon.runtime.core.injection.AbstractModule;
import org.kordamp.jipsy.ServiceProviderFor;

@ServiceProviderFor(Module.class)
public class ApplicationModule extends AbstractModule {
    @Override
    protected void doConfigure() {
        bind(JpaBootstrap.class)
            .to(SampleJpaBootstrap.class)
            .asSingleton();
    }
}

2.2. Example

The following is a trivial usage of the EntityManagerHandler inside a Java service

com.acme.SampleService.java

package com.acme;

import griffon.core.artifact.GriffonService;
import griffon.metadata.ArtifactProviderFor;
import org.codehaus.griffon.runtime.core.artifact.AbstractGriffonService;

import griffon.plugins.jpa.EntityManagerHandler;
import griffon.plugins.jpa.EntityManagerCallback;
import javax.persistence.EntityManager;

import javax.annotation.Nonnull;
import javax.inject.Inject;

@ArtifactProviderFor(GriffonService.class)
public class SampleService extends AbstractGriffonService {
    @Inject
    private EntityManagerHandler entityManagerHandler;

    public String getPersonName(final int id) {
         return entityManagerHandler.withEntityManager(new EntityManagerCallback<String>() {
             public String handle(@Nonnull String persistenceUnitName, @Nonnull EntityManager entityManager) {
                 Person p = (Person) entityManager.createQuery('select p from Person p').getSingleResult();
                 return p != null ? p.gteName() : null;
         });
    }
}

Here’s the Groovy version of it

com.acme.SampleService.groovy

package com.acme

import griffon.core.artifact.GriffonService
import griffon.metadata.ArtifactProviderFor

import griffon.plugins.jpa.EntityManagerHandler
import javax.persistence.EntityManager

import javax.inject.Inject

@ArtifactProviderFor(GriffonService)
class SampleService {
    @Inject
    private EntityManagerHandler entityManagerHandler

    String getPersonName(int id) {
         entityManagerHandler.withEntityManager { String persistenceUnitName, EntityManager entityManager ->
             entityManager.createQuery('select p from Person p').singleResult?.name ?: null
         }
    }
}

2.3. Events

The following events will be triggered by EntityManagerHandler

JpaConnectStart(String persistenceUnitName, Map<String, Object> config): Triggered before connecting to the database.
JpaConnectEnd(String persistenceUnitName, Map<String, Object> config, EntityManager entityManager): Triggered after connecting to the database.
JpaDisconnectStart(String persistenceUnitName, Map<String, Object> config, EntityManager entityManager): Triggered before disconnecting from the database.
JpaDisconnectEnd(String persistenceUnitName, Map<String, Object> config): Triggered after disconnecting from the database.

DataSource events may be triggered during connection and disconnection from a EntityManager.

2.4. AST Transformation

You can apply the @EntityManagerAware AST transformation on any class. This injects the behavior of EntityManagerHandler into said class. The previous Groovy service example can be rewritten as follows

com.acme.SampleService.groovy

package com.acme

import griffon.core.artifact.GriffonService
import griffon.metadata.ArtifactProviderFor
import griffon.transform.EntityManagerAware

import com.j256.jpa.support.EntityManager

@EntityManagerAware
@ArtifactProviderFor(GriffonService)
class SampleService {
    String getPersonName(int id) {
         withEntityManager { String persistenceUnitName, EntityManager entityManager ->
             entityManager.createQuery('select p from Person p').singleResult?.name ?: null
         }
    }
}

2.5. DSL Descriptors

This plugin provides DSL descriptors for Intellij IDEA and Eclipse (provided you have the Groovy Eclipse plugin installed). These descriptors are found inside the griffon-jpa-groovy-compile-2.1.0.jar, with locations

dsdl/griffon_jpa.dsld
gdsl/griffon_jpa.gdsl

3. Build Configuration

3.1. Gradle

You have two options for configuring this plugin: automatic and manual.

3.1.1. Automatic

As long as the project has the org.codehaus.griffon.griffon plugin applied to it you may include the following snippet in build.gradle

dependencies {
    griffon 'org.codehaus.griffon.plugins:griffon-jpa-plugin:2.1.0'
}

The griffon plugin will take care of the rest given its configuration.

3.1.2. Manual

You will need to configure any of the following blocks depending on your setup

dependencies {
    compile 'org.codehaus.griffon.plugins:griffon-jpa-core:2.1.0'
}

Compile Only

dependencies {
    compileOnly 'org.codehaus.griffon.plugins:griffon-jpa-groovy-compile:2.1.0'
}

3.2. Maven

First configure the griffon-jpa-plugin BOM in your POM file, by placing the following snippet before the <build> element

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.codehaus.griffon.plugins</groupId>
            <artifactId>griffon-jpa-plugin</artifactId>
            <version>2.1.0</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

Next configure dependencies as required by your particular setup

<dependency>
    <groupId>org.codehaus.griffon.plugins</groupId>
    <artifactId>griffon-jpa-core</artifactId>
</dependency>

Provided scope

<dependency>
    <groupId>org.codehaus.griffon.plugins</groupId>
    <artifactId>griffon-jpa-groovy-compile</artifactId>
</dependency>

Don’t forget to configure all -compile dependencies with the maven-surefire-plugin, like so

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <classpathDependencyExcludes>
            <classpathDependencyExclude>
                org.codehaus.griffon:griffon-jpa-groovy-compile
            </classpathDependencyExclude>
        </classpathDependencyExcludes>
    </configuration>
</plugin>

4. Modules

The following sections display all bindings per module. Use this information to successfully override a binding on your own modules or to troubleshoot a module binding if the wrong type has been applied by the Griffon runtime.

4.1. Jpa

Module name: jpa

bind(ResourceBundle.class)
    .withClassifier(named("jpa"))
    .toProvider(new ResourceBundleProvider("Jpa"))
    .asSingleton();

bind(Configuration.class)
    .withClassifier(named("jpa"))
    .to(DefaultJpaConfiguration.class)
    .asSingleton();

bind(JpaSettingsStorage.class)
    .to(DefaultJpaSettingsStorage.class)
    .asSingleton();

bind(JpaSettingsFactory.class)
    .to(DefaultJpaSettingsFactory.class)
    .asSingleton();

bind(EntityManagerHandler.class)
    .to(DefaultEntityManagerHandler.class)
    .asSingleton();

bind(GriffonAddon.class)
    .to(JpaAddon.class)
    .asSingleton();

5. Links

Javadoc

API Sources