Configure JPA during run time, dynamic JPA Configuration using Spring context

You can set the database information during run time. Then remove all the database specific stuff
from persistance.xml and use Hash properties in your java class.

1. Removed all your database properties from persistance.xml
<persistence>
<persistence-unit name="jpablogPUnit" transaction-type="RESOURCE_LOCAL">
<class>com.suman.Company</class>
</persistence-unit>
</persistence>

2. Changed your java file where you are configuring entityManager, in our case TestApplication.java


package com.suman;

import java.util.HashMap;
import java.util.Map;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import org.apache.log4j.Logger;

/**
* @author Binod Suman
*/
public class TestApplication {

Logger log = Logger.getLogger(TestApplication.class);
public static void main(String[] args) {
TestApplication test = new TestApplication();
test.saveCompany();
}

public void saveCompany(){
log.info("Company data is going to save");
EntityManagerFactory emf;
Map properties = new HashMap();
properties.put("hibernate.connection.driver_class", "com.mysql.jdbc.Driver");
properties.put("hibernate.connection.url", "jdbc:mysql://localhost:3306/sumandb");
properties.put("hibernate.connection.username", "root");
properties.put("hibernate.connection.password", "mysql");
properties.put("hibernate.dialect", "org.hibernate.dialect.MySQLDialect");
properties.put("hibernate.show-sql", "true");
//emf = Persistence.createEntityManagerFactory("jpablogPUnit");
emf = Persistence.createEntityManagerFactory("jpablogPUnit",properties);
EntityManager entityManager = (EntityManager) emf.createEntityManager();
entityManager.getTransaction().begin();
Company company = new Company(120,"TecnoTree","Espoo, Finland");
entityManager.persist(company);
entityManager.getTransaction().commit();
log.info("Company data has been saved");
}

}

Now run the application.
One more record has been inserted.

How to fetch data using JPA

Change the code of TestApplcation.java

package com.suman;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

import org.apache.log4j.Logger;

/**
* @author Binod Suman
*/
public class TestApplication {

Logger log = Logger.getLogger(TestApplication.class);
EntityManagerFactory emf;
EntityManager em;

public static void main(String[] args) {
TestApplication test = new TestApplication();
test.configureEntityManager();
// test.saveCompany();
test.fetchCompanyData();
}

public void configureEntityManager(){
Map properties = new HashMap();
properties.put("hibernate.connection.driver_class", "com.mysql.jdbc.Driver");
properties.put("hibernate.connection.url", "jdbc:mysql://localhost:3306/sumandb");
properties.put("hibernate.connection.username", "root");
properties.put("hibernate.connection.password", "mysql");
properties.put("hibernate.dialect", "org.hibernate.dialect.MySQLDialect");
properties.put("hibernate.show-sql", "true");
//emf = Persistence.createEntityManagerFactory("jpablogPUnit");
emf = Persistence.createEntityManagerFactory("jpablogPUnit",properties);
em = emf.createEntityManager();
}

public void saveCompany(){
log.info("Company data is going to save");
EntityManager entityManager = (EntityManager) emf.createEntityManager();
entityManager.getTransaction().begin();
Company company = new Company(120,"TecnoTree","Espoo, Finland");
entityManager.persist(company);
entityManager.getTransaction().commit();
log.info("Company data has been saved");
}

public void fetchCompanyData(){
Query query = em.createQuery("SELECT c FROM Company c");
List<Company> list = (List<Company>) query.getResultList();
log.info(list);

for (Company company : list) {
log.info("Company Name :: "+company.getName());
log.info("Company City :: "+company.getCity());
log.info("***************************");
}
}
}


You can configure the EntityManagerFactory from spring configuration file also.

<bean id="entityManagerFactory"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"
lazy-init="false">
<property name="persistenceUnitName" value="VMSPersistenceUnit" />
<property name="dataSource" ref="sourceDataSource" />
<property name="loadTimeWeaver">
<bean class="org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver" />
</property>
</bean>

If you want to configure entityManagerFactory during runt time then use these code. As if you dont have database name and information then you can not use the spring context for entityManagerFactory.


private EntityManagerFactory entityManagerFactory;
private JpaTemplate jpaTemplate;


LocalContainerEntityManagerFactoryBean bean = new LocalContainerEntityManagerFactoryBean();
bean.setDataSource(sourceDataSource);
bean.afterPropertiesSet();
entityManagerFactory = bean.getObject();
log.info("entityManagerFactory :: " + entityManagerFactory);
this.jpaTemplate = new JpaTemplate(this.entityManagerFactory);

Even you can fetch record in batch wise manner also.
Use this below code:
public Collection fetchQueryListFromSourceDatabaseForSubscriber(final String sql,final int firstPosition, final int numberOfRecords) throws DataAccessException {
return (Collection) this.jpaTemplate.execute(new JpaCallback() {
public Object doInJpa(EntityManager em) throws PersistenceException {
Query query = em.createQuery(sql);
query.setFirstResult(firstPosition);
query.setMaxResults(numberOfRecords);
List result = query.getResultList();
return result;
}
});
}

If will fetch record from firstPosition and number of record will be numberOfRecords.
A persistence provider may or may not optimize access to database using database specific limit clause, like select * from table limit 10,

Then in TestApplication.java

public Collection fetchQueryListFromSourceDatabase(final String sql) throws DataAccessException {
return (Collection) this.jpaTemplate.execute(new JpaCallback() {
public Object doInJpa(EntityManager em) throws PersistenceException {
Query query = em.createQuery(sql);
List result = query.getResultList();
log.info("FINALLY JPA WORKING :: "+result.size());
return result;
}
});
}

Please feedback to improve this tutorial ....... :)

Thanks :)