How to support multiple databases engines on Spring? - spring

Question

I’m building a Spring Boot application that should support various databases engines (MySQL, PostgreSQL, Oracle, SQL Server).
The user will be prompted to select which database it would like to use when installing the application and all tables will be created after this. I think that I should save the user option somewhere and then use it to select the right engine that my application will use to instantiate the repositories.
I googled for some references or best practices that I should follow to implement this but wasn’t able to find (maybe I’m searching the wrong terms - sorry).
Do you have any resource that points me to the right direction?
Thanks a lot!!!

Answer 1

You can refer sample. In sample I use hibernate + spring boot for multiple databases.
You can work by this way:
Step 1: you declare in application.properties info connect of database (mysql, oracle, postgresql)
# MySQL-Database
mysql.db.driver: com.mysql.jdbc.Driver
mysql.db.url: jdbc:mysql://localhost:3306/test
mysql.db.username: root
mysql.db.password: root
mysql.hibernate.dialect: org.hibernate.dialect.MySQL5Dialect
mysql.entitymanager.packagesToScan: com.test.mysql
# postgresql-Database
postgresql.db.driver: org.postgresql.Driver
postgresql.db.url: jdbc:postgresql://localhost:5432/postgres_demo
postgresql.db.username: root
postgresql.db.password:
postgresql.hibernate.dialect: org.hibernate.dialect.PostgreSQLDialect
postgresql.entitymanager.packagesToScan: com.test.postgresql
# Oracle-Database
oracle.db.driver: oracle.jdbc.driver.OracleDriver
oracle.db.url: jdbc:oracle:thin:#localhost:1521:xe
oracle.db.username: root
oracle.db.password:
oracle.hibernate.dialect: org.hibernate.dialect.Oracle10gDialect
oracle.entitymanager.packagesToScan: com.test.oracle
Step 2: In project spring boot you can refer structure project such as:
Step 3 : Implement data source for mysql, oracle, postgresql. you can refer MysqlDatabaseConfig.java, OracleDatabaseConfig.java, PostgresDatabaseConfig.java
package com.test.mysql;
import java.util.Properties;
import javax.sql.DataSource;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.hibernate4.HibernateTransactionManager;
import org.springframework.orm.hibernate4.LocalSessionFactoryBean;
import org.springframework.transaction.annotation.EnableTransactionManagement;
#Configuration
#EnableTransactionManagement
public class MysqlDatabaseConfig {
#Value("${mysql.db.driver}")
private String DB_DRIVER;
#Value("${mysql.db.password}")
private String DB_PASSWORD;
#Value("${mysql.db.url}")
private String DB_URL;
#Value("${mysql.db.username}")
private String DB_USERNAME;
#Value("${mysql.hibernate.dialect}")
private String HIBERNATE_DIALECT;
#Value("${mysql.entitymanager.packagesToScan}")
private String ENTITYMANAGER_PACKAGES_TO_SCAN;
#Bean(name="mysqlDataSource")
#Primary
public DataSource cmrDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(DB_DRIVER);
dataSource.setUrl(DB_URL);
dataSource.setUsername(DB_USERNAME);
dataSource.setPassword(DB_PASSWORD);
return dataSource;
}
#Bean(name="mysqlSessionFactory")
public LocalSessionFactoryBean crmSessionFactory() {
LocalSessionFactoryBean sessionFactoryBean = new LocalSessionFactoryBean();
sessionFactoryBean.setDataSource(cmrDataSource());
sessionFactoryBean.setPackagesToScan(ENTITYMANAGER_PACKAGES_TO_SCAN);
Properties hibernateProperties = new Properties();
hibernateProperties.put("hibernate.dialect", HIBERNATE_DIALECT);
sessionFactoryBean.setHibernateProperties(hibernateProperties);
return sessionFactoryBean;
}
#Bean(name="mysqlTransactionManager")
public HibernateTransactionManager transactionManager() {
HibernateTransactionManager transactionManager = new HibernateTransactionManager();
transactionManager.setSessionFactory(crmSessionFactory().getObject());
return transactionManager;
}
}
OracleDatabaseConfig.java
package com.test.oracle;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.hibernate4.HibernateTransactionManager;
import org.springframework.orm.hibernate4.LocalSessionFactoryBean;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import javax.sql.DataSource;
import java.util.Properties;
#Configuration
#EnableTransactionManagement
public class OracleDatabaseConfig {
#Value("${oracle.db.driver}")
private String DB_DRIVER;
#Value("${oracle.db.password}")
private String DB_PASSWORD;
#Value("${oracle.db.url}")
private String DB_URL;
#Value("${oracle.db.username}")
private String DB_USERNAME;
#Value("${oracle.hibernate.dialect}")
private String HIBERNATE_DIALECT;
#Value("${oracle.entitymanager.packagesToScan}")
private String ENTITYMANAGER_PACKAGES_TO_SCAN;
#Bean(name="oracleDataSource")
#Primary
public DataSource cmrDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(DB_DRIVER);
dataSource.setUrl(DB_URL);
dataSource.setUsername(DB_USERNAME);
dataSource.setPassword(DB_PASSWORD);
return dataSource;
}
#Bean(name="oracleSessionFactory")
public LocalSessionFactoryBean crmSessionFactory() {
LocalSessionFactoryBean sessionFactoryBean = new LocalSessionFactoryBean();
sessionFactoryBean.setDataSource(cmrDataSource());
sessionFactoryBean.setPackagesToScan(ENTITYMANAGER_PACKAGES_TO_SCAN);
Properties hibernateProperties = new Properties();
hibernateProperties.put("hibernate.dialect", HIBERNATE_DIALECT);
sessionFactoryBean.setHibernateProperties(hibernateProperties);
return sessionFactoryBean;
}
#Bean(name="oracleTransactionManager")
public HibernateTransactionManager transactionManager() {
HibernateTransactionManager transactionManager = new HibernateTransactionManager();
transactionManager.setSessionFactory(crmSessionFactory().getObject());
return transactionManager;
}
}
PostgresDatabaseConfig.java
package com.test.postgresql;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.hibernate4.HibernateTransactionManager;
import org.springframework.orm.hibernate4.LocalSessionFactoryBean;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import javax.sql.DataSource;
import java.util.Properties;
#Configuration
#EnableTransactionManagement
public class PostgresDatabaseConfig {
#Value("${postgresql.db.driver}")
private String DB_DRIVER;
#Value("${postgresql.db.password}")
private String DB_PASSWORD;
#Value("${postgresql.db.url}")
private String DB_URL;
#Value("${postgresql.db.username}")
private String DB_USERNAME;
#Value("${postgresql.hibernate.dialect}")
private String HIBERNATE_DIALECT;
#Value("${postgresql.entitymanager.packagesToScan}")
private String ENTITYMANAGER_PACKAGES_TO_SCAN;
#Bean(name="postgresqlDataSource")
#Primary
public DataSource cmrDataSource() {
DriverManagerDataSource dataSource = new DriverManagerDataSource();
dataSource.setDriverClassName(DB_DRIVER);
dataSource.setUrl(DB_URL);
dataSource.setUsername(DB_USERNAME);
dataSource.setPassword(DB_PASSWORD);
return dataSource;
}
#Bean(name="postgresqlSessionFactory")
public LocalSessionFactoryBean crmSessionFactory() {
LocalSessionFactoryBean sessionFactoryBean = new LocalSessionFactoryBean();
sessionFactoryBean.setDataSource(cmrDataSource());
sessionFactoryBean.setPackagesToScan(ENTITYMANAGER_PACKAGES_TO_SCAN);
Properties hibernateProperties = new Properties();
hibernateProperties.put("hibernate.dialect", HIBERNATE_DIALECT);
sessionFactoryBean.setHibernateProperties(hibernateProperties);
return sessionFactoryBean;
}
#Bean(name="postgresqlTransactionManager")
public HibernateTransactionManager transactionManager() {
HibernateTransactionManager transactionManager = new HibernateTransactionManager();
transactionManager.setSessionFactory(crmSessionFactory().getObject());
return transactionManager;
}
}
Step 4: call to use:
in case mysql
package com.test.mysql.dao;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
#Repository
#Transactional("mysqlTransactionManager")
public class TestMysqlDao {
#Autowired
#Qualifier("mysqlSessionFactory")
private SessionFactory sessionFactory;
}
In case oracle
package com.test.oracle.dao;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
#Repository
#Transactional("oracleTransactionManager")
public class TestOracleDao {
#Autowired
#Qualifier("oracleSessionFactory")
private SessionFactory sessionFactory;
}
In case postgresql
package com.test.postgresql.dao;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
#Repository
#Transactional("postgresqlTransactionManager")
public class TestPostgresDao {
#Autowired
#Qualifier("postgresqlSessionFactory")
private SessionFactory sessionFactory;
}

Answer 2

It's unclear what you mean by installing but if you want your application to start with different databases you can use different Spring profiles with your application.yml Spring boot profiles
---
spring:
profiles: postgres
datasource:
url:
username:
password:
driver-class-name: org.postgresql.Driver
---
spring:
profiles: mysql
datasource:
url:
username:
password:
driver-class-name: com.mysql.jdbc.Driver
You can then start the application with the respective profile
java -jar -Dspring.profiles.active=mysql yourapp.jar

Answer 3

You can define different connections and get them with specific methods
private DataSource mySqlDataSource;
private DataSource postgresDataSource;
public Connection getMySqlConnection() throws SQLException {
mySqlDataSource.getConnection();
}
public Connection getPostgresConnection() throws SQLException {
postgresDataSource.getConnection();
}