Distributed transactions with multiple databases, Spring Boot, Spring Data JPA and Atomikos

A couple of weeks ago I was evaluating the possibility to use Spring Boot, Spring Data JPA and Atomikos for distributed transactions involving multiple databases. After looking at the

Spring blog article (which involves one database and ActiveMQ) and having done some attempts, I could not get it to work with two databases. The configuration seemed fine, but the Entity Manager did not get notified when persisting my entities. So I wrote

this question on StackOverflow, which has been answered directly by
Dave Syer and
Oliver Gierke. This post is to share and discuss the solution.

Description of the case and entities model

We want to be able to save two entities at the same time into two different databases; the operation must be transactional. So, in this example, we have a Customer entity, which is persisted in the first database, and an Order entity which is persisted in
the second database. The two entities are very simple, as they serve only as a demonstration.



The resulting implementation is the following. It's worth noting that they belong to two different packages, for two main reasons:

it's a logical separation that gives order to the project
each repository will scan packages containing only entities that it will be going to manage

package com.at.mul.domain.customer;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.Data;
import lombok.EqualsAndHashCode;

@Entity
@Table(name = "customer")
@Data
@EqualsAndHashCode(exclude = { "id" })
public class Customer {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;

@Column(name = "name", nullable = false)
private String name;

@Column(name = "age", nullable = false)
private Integer age;

}

package com.at.mul.domain.order;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import lombok.Data;
import lombok.EqualsAndHashCode;

@Entity
@Table(name = "orders")
@Data
@EqualsAndHashCode(exclude = { "id" })
public class Order {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;

@Column(name = "code", nullable = false)
private Integer code;

@Column(name = "quantity", nullable = false)
private Integer quantity;

}

See
Lombok for annotations like

@Data

and

@EqualsAndHashCode

Write repositories interfaces

Also in this case it's standard, the only thing to notice is that I put the two interfaces in two different packages. The reason is explained in the next step.

package com.at.mul.repository.customer;

import org.springframework.data.jpa.repository.JpaRepository;

import com.at.mul.domain.customer.Customer;

public interface CustomerRepository extends JpaRepository<Customer, Integer> {

}

package com.at.mul.repository.order;

import org.springframework.data.jpa.repository.JpaRepository;

import com.at.mul.domain.order.Order;

public interface OrderRepository extends JpaRepository<Order, Integer> {

}

Write configuration classes

This is where it becomes interesting. The

@DependsOn("transactionManager")

annotation is not mandatory, but I needed this to get rid of several warnings at tests (or application) startup, like

WARNING: transaction manager not running?

in the logs. The next annotation

@EnableJpaRepositories

is more important:

it specifies which are the packages to scan for annotated components (repository interfaces), and in my case I wanted only repositories related to the
customer (and conversely to the order).
it specifies which is the entity manager to be used to manage entities, in my case the

customerEntityManager

for customer related operations and

orderEntityManager

for order related operations
it specifies the transaction manager to be used, in my case the

transactionManager

defined in the

MainConfig

class. This needs to be the same for every

@EnableJpaRepositories

to get distributed transactions working

package com.at.mul;

import java.util.HashMap;

import javax.sql.DataSource;

import org.h2.jdbcx.JdbcDataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaVendorAdapter;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

import com.at.mul.repository.customer.CustomerDatasourceProperties;
import com.atomikos.jdbc.AtomikosDataSourceBean;

@Configuration
@DependsOn("transactionManager")
@EnableJpaRepositories(basePackages = "com.at.mul.repository.customer", entityManagerFactoryRef = "customerEntityManager", transactionManagerRef = "transactionManager")
@EnableConfigurationProperties(CustomerDatasourceProperties.class)
public class CustomerConfig {

@Autowired
private JpaVendorAdapter jpaVendorAdapter;

@Autowired
private CustomerDatasourceProperties customerDatasourceProperties;

@Bean(name = "customerDataSource", initMethod = "init", destroyMethod = "close")
public DataSource customerDataSource() {
JdbcDataSource h2XaDataSource = new JdbcDataSource();
h2XaDataSource.setURL(customerDatasourceProperties.getUrl());

AtomikosDataSourceBean xaDataSource = new AtomikosDataSourceBean();
xaDataSource.setXaDataSource(h2XaDataSource);
xaDataSource.setUniqueResourceName("xads1");
return xaDataSource;
}

@Bean(name = "customerEntityManager")
@DependsOn("transactionManager")
public LocalContainerEntityManagerFactoryBean customerEntityManager() throws Throwable {

HashMap<String, Object> properties = new HashMap<String, Object>();
properties.put("hibernate.transaction.jta.platform", AtomikosJtaPlatform.class.getName());
properties.put("javax.persistence.transactionType", "JTA");

LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean();
entityManager.setJtaDataSource(customerDataSource());
entityManager.setJpaVendorAdapter(jpaVendorAdapter);
entityManager.setPackagesToScan("com.at.mul.domain.customer");
entityManager.setPersistenceUnitName("customerPersistenceUnit");
entityManager.setJpaPropertyMap(properties);
return entityManager;
}

}

package com.at.mul;

import java.util.HashMap;

import javax.sql.DataSource;

import org.h2.jdbcx.JdbcDataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaVendorAdapter;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;

import com.at.mul.repository.order.OrderDatasourceProperties;
import com.atomikos.jdbc.AtomikosDataSourceBean;

@Configuration
@DependsOn("transactionManager")
@EnableJpaRepositories(basePackages = "com.at.mul.repository.order", entityManagerFactoryRef = "orderEntityManager", transactionManagerRef = "transactionManager")
@EnableConfigurationProperties(OrderDatasourceProperties.class)
public class OrderConfig {

@Autowired
private JpaVendorAdapter jpaVendorAdapter;

@Autowired
private OrderDatasourceProperties orderDatasourceProperties;

@Bean(name = "orderDataSource", initMethod = "init", destroyMethod = "close")
public DataSource orderDataSource() {
JdbcDataSource h2XaDataSource = new JdbcDataSource();
h2XaDataSource.setURL(orderDatasourceProperties.getUrl());

AtomikosDataSourceBean xaDataSource = new AtomikosDataSourceBean();
xaDataSource.setXaDataSource(h2XaDataSource);
xaDataSource.setUniqueResourceName("xads2");
return xaDataSource;
}

@Bean(name = "orderEntityManager")
public LocalContainerEntityManagerFactoryBean orderEntityManager() throws Throwable {

HashMap<String, Object> properties = new HashMap<String, Object>();
properties.put("hibernate.transaction.jta.platform", AtomikosJtaPlatform.class.getName());
properties.put("javax.persistence.transactionType", "JTA");

LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean();
entityManager.setJtaDataSource(orderDataSource());
entityManager.setJpaVendorAdapter(jpaVendorAdapter);
entityManager.setPackagesToScan("com.at.mul.domain.order");
entityManager.setPersistenceUnitName("orderPersistenceUnit");
entityManager.setJpaPropertyMap(properties);
return entityManager;
}

}

Another important thing here is the definition of the

LocalContainerEntityManagerFactoryBean

.

the

@Bean

annotation has a given

name

, that is the one specified in the

@EnableJpaRepositories

annotation.
you need to set some properties to the

JpaPropertyMap

, in particular you need to say that the transaction type is JTA and that the jta platform is

AtomikosJtaPlatform.class.getName()

Not setting the second property was the reason why I could not get it work. As Dave Syer wrote "It seems Hibernate4 doesn't work with Atomikos out of the box", so you need to implement the class to be set as

hibernate.transaction.jta.platform

property by yourself. In my opinion this is not very well documented, but fortunately Oliver Gierke found another

StackOverflow discussion about this topic. If you are using another JTA provider, you may find

this useful.

Write the AbstractJtaPlatform implementation

As said, this is the most important step, as we need to write the implementation of that class by ourselves since Hibernate does not provide it. Here is the resulting code:

package com.at.mul;

import javax.transaction.TransactionManager;
import javax.transaction.UserTransaction;

import org.hibernate.engine.transaction.jta.platform.internal.AbstractJtaPlatform;

public class AtomikosJtaPlatform extends AbstractJtaPlatform {

private static final long serialVersionUID = 1L;

static TransactionManager transactionManager;
static UserTransaction transaction;

@Override
protected TransactionManager locateTransactionManager() {
return transactionManager;
}

@Override
protected UserTransaction locateUserTransaction() {
return transaction;
}

}

Write the main configuration class

Also in this case it's a pretty standard class, with

@EnableTransactionManagement

annotation and Atomikos bean definitions. The only
very important thing to notice is that we need to set

AtomikosJtaPlatform.transactionManager

and

AtomikosJtaPlatform.transaction

attributes.

package com.at.mul;

import javax.transaction.TransactionManager;
import javax.transaction.UserTransaction;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.DependsOn;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.orm.jpa.JpaVendorAdapter;
import org.springframework.orm.jpa.vendor.Database;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import org.springframework.transaction.jta.JtaTransactionManager;

import com.atomikos.icatch.jta.UserTransactionImp;
import com.atomikos.icatch.jta.UserTransactionManager;

@Configuration
@ComponentScan
@EnableTransactionManagement
public class MainConfig {

@Bean
public PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
return new PropertySourcesPlaceholderConfigurer();
}

@Bean
public JpaVendorAdapter jpaVendorAdapter() {
HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter();
hibernateJpaVendorAdapter.setShowSql(true);
hibernateJpaVendorAdapter.setGenerateDdl(true);
hibernateJpaVendorAdapter.setDatabase(Database.H2);
return hibernateJpaVendorAdapter;
}

@Bean(name = "userTransaction")
public UserTransaction userTransaction() throws Throwable {
UserTransactionImp userTransactionImp = new UserTransactionImp();
userTransactionImp.setTransactionTimeout(10000);
return userTransactionImp;
}

@Bean(name = "atomikosTransactionManager", initMethod = "init", destroyMethod = "close")
public TransactionManager atomikosTransactionManager() throws Throwable {
UserTransactionManager userTransactionManager = new UserTransactionManager();
userTransactionManager.setForceShutdown(false);

AtomikosJtaPlatform.transactionManager = userTransactionManager;

return userTransactionManager;
}

@Bean(name = "transactionManager")
@DependsOn({ "userTransaction", "atomikosTransactionManager" })
public PlatformTransactionManager transactionManager() throws Throwable {
UserTransaction userTransaction = userTransaction();

AtomikosJtaPlatform.transaction = userTransaction;

TransactionManager atomikosTransactionManager = atomikosTransactionManager();
return new JtaTransactionManager(userTransaction, atomikosTransactionManager);
}

}

Resources

Here is the resulting structure of the project:



You can see the full source code here: https://github.com/fabiomaffioletti/mul-at, The

master

branch uses in memory database. Checkout branch named

mysql-db

to use real databases (see

application.properties

to tweak your database connection data).