Microservice: Creating JPA Application Using Jakarta Persistence API in Payara Micro

In this blog, we will discuss how your Java microservice application can connect to and interact with a relational database through the Jakarta Persistence API (the latest version at the time of writing is version 3.0). You can configure a data source and a JDBC driver so an application that is running on your Payara Microserver can connect with a relational database.

Before We Begin:

In this tutorial, we will configure this application with the following components in mind:

  • The microservice application will be a Mavenized Java application.
  • We will use MySQL DB Server as a relational database.
  • The JDBC data source will be a transactional data source (XADataSource).

JDBC Driver Library Configuration With Maven

You need a JDBC driver to connect your Java application with a relational database. The driver is usually provided by the database vendor. Fortunately, most database vendors have released their JDBC drivers to a Maven repository.

If you use Maven to build your application, you can add your JDBC driver by adding code that is similar to the following example to your pom.xml file.

    <dependencyManagement>
    	<dependencies>
    		<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    		<dependency>
    			<groupId>mysql</groupId>
    			<artifactId>mysql-connector-java</artifactId>
    			<version>8.0.19</version>
    		</dependency>
    	</dependencies>
    </dependencyManagement>
    
    <dependencies>
    	<dependency>
    		<groupId>mysql</groupId>
    		<artifactId>mysql-connector-java</artifactId>
    	</dependency>
    </dependencies>

With Maven, the JDBC driver file will be copied to the WEB-INF/lib folder of your application WAR file during the package build phase.

Configuring a Database Datasource

In the Payara Bloga data source is configured inside the web.xml file. In this example, there is another alternative for creating a data source configuration. The example below demonstrates a basic data source configuration pattern for the payara-resource.xml file inside the src/main/java/webapp/WEB-INF folder:

    <!DOCTYPE resources  PUBLIC  "-//Payara.fish//DTD Payara Server 4 Resource Definitions//EN"  "https://raw.githubusercontent.com/payara/Payara-Community-Documentation/master/docs/modules/ROOT/pages/schemas/payara-resources_1_6.dtd">
    <resources>
        <jdbc-resource pool-name="MyAppDS"
                       jndi-name="java:app/jdbc/MyApp"
                       enable="true"/>
        <jdbc-connection-pool name="MySQLPool"
                              res-type="javax.sql.XADataSource"
                              datasource-classname="com.mysql.cj.jdbc.MysqlXADataSource">
            <property name="url" value="jdbc:h2:mem:hibernateExample"/>
<property name="User" value="testUser"></property>
            <property name="Password" value="testPassword"></property>
            <property name="DatabaseName" value="myapp_db"></property>
            <property name="ServerName" value="localhost"></property>
            <property name="PortNumber" value="3306"></property>
        </jdbc-connection-pool>
    </resources>

Application Configuration for Relational Database Connections

To use a data source that is configured in your payara-resource.xml file, you can either inject the data source or specify a lookup in your application code. The following examples assume that a jndi-name value of java:app/jdbc/MyApp is specified as the jdbc-resource element attribute in the payara-resource.xml file.

@Resource(name= "java:app/jdbc/MyApp") 
DataSource myDB;

Injecting JPA EntityManager Into Your Application

Once your data source is configured in your payara-resource.xml file, we need to register your data source inside the persistence.xml in your src/main/resources/META-INF/persistence.xml file. The jta-data-source is and matches the jndi-name of the data source as specified in the payara-resource.xml.

    <?xml version="1.0" encoding="UTF-8"?>
    <persistence version="2.1"
    	xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    	xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd ">
    	<persistence-unit name="MyAppPU" transaction-type="JTA">
    		<jta-data-source>java:app/jdbc/MyApp</jta-data-source>
    		<shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>
    		<properties>
    			<!-- JBoss Wildfly's Hibernate 4 specific JPA properties -->
    			<property name="hibernate.cache.use_second_level_cache" value="true" />
    			<property name="hibernate.hbm2ddl.auto" value="validate" /><!-- NEVER: update -->
            	<property name="hibernate.show_sql" value="false" />
            	<property name="hibernate.format_sql" value="false"/>
    			<property name="hibernate.use_sql_comments" value="false" />
    			<property name="hibernate.enable_lazy_load_no_trans" value="true"/>
    			<!--  For Performance monitoring on Hibernate -->
    			<property name="hibernate.generate_statistics" value="false"/>
    			<property name="hibernate.cache.use_structured_entries" value="false"/>
    			
    			<!-- TomEE PluME 1.7.2 and higher with EclipseLink  -->
    			<property name="eclipselink.logging.logger" value="JavaLogger" />
    		</properties>
    	</persistence-unit>
    </persistence>

You can inject your jakarta.persistence.EntityManager in your Java application code by specifying your persistence unit MyAppPU in your PersistenceContext annotation:

@PersistenceContext(unitName="MyAppPU")
private EntityManager entityManager;

With that, you can get your Java microservice application to connect and interact with a relational database through the Jakarta Persistence API!

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