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下面这个小项目展示了如何连接2个数据库，一个是Oracle，一个是MySQL。

关键的Maven依赖：

    
    
     org.springframework.boot
     
    
     spring-boot-starter-data-jpa
    
    
   
    
    
     com.oracle
     
    
     ojdbc6
     
    
     11.2.0
    
    
   
    
    
     mysql
     
    
     mysql-connector-java
    
   

这个Oracle的jar包是不再maven仓库里面的，需要自己手动导入到maven仓库。

application.properties的代码如下：

#Oracle DB Configdb.dialect=org.hibernate.dialect.Oracle10gDialectdb.driver=oracle.jdbc.driver.OracleDriverdb.url=jdbc:oracle:thin:@localhost:1521:xedb.user=pavansdb.password=******#MySQL DB Configmysql.db.dialect=org.hibernate.dialect.MySQLDialectmysql.db.driver=com.mysql.jdbc.Drivermysql.db.url=jdbc:mysql://localhost:3306/localdb?useSSL=falsemysql.db.user=lessrootmysql.db.password=******

所以，要定义2个dataSource的Bean，Spring需要知道那个dataSource是主要的，哪个是次要的。如果不去定义主次，那么Spring程序将会启动失败。如果不定义主次，那么相同的bean，Spring是不能将其注册的。

使用@Primary注解定义主要的dataSource的Bean。

首要的DtaSource配置：

@Configuration@EnableTransactionManagement@EnableJpaRepositories(		entityManagerFactoryRef = "entityManagerFactory", 		transactionManagerRef = "transactionManager", 		basePackages = "com.opencodez.dao.oracle.repo")public class PrimaryDbConfig {	public static final String PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE = "hibernate.jdbc.batch_size";	public static final String PROPERTY_NAME_HIBERNATE_SHOW_SQL = "hibernate.show_sql";	public static final String PROPERTY_NAME_HIBERNATE_FMT_SQL = "hibernate.format_sql";	public static final String[] ENTITYMANAGER_PACKAGES_TO_SCAN = { "com.opencodez.dao.oracle.domain" };	public static final String DB_URL = "db.url";	public static final String DB_USER = "db.user";	public static final String DB_PASSWORD = "db.password";	public static final String DB_DRIVER = "db.driver";	public static final String DB_DIALECT = "db.dialect";		@Autowired	private Environment env;		@Bean	public AnnotationMBeanExporter annotationMBeanExporter() {	    AnnotationMBeanExporter annotationMBeanExporter = new AnnotationMBeanExporter();	    annotationMBeanExporter.addExcludedBean("dataSource");	    annotationMBeanExporter.setRegistrationPolicy(RegistrationPolicy.IGNORE_EXISTING);	    return annotationMBeanExporter;	}		@Bean(destroyMethod = "close")	@Primary	public DataSource dataSource() {		ComboPooledDataSource dataSource = new ComboPooledDataSource();		try {			dataSource.setDriverClass(env.getProperty(DB_DRIVER));		} catch (PropertyVetoException e) {			e.printStackTrace();		}		dataSource.setJdbcUrl(env.getProperty(DB_URL));		dataSource.setUser(env.getProperty(DB_USER));		dataSource.setPassword(env.getProperty(DB_PASSWORD));		dataSource.setAcquireIncrement(5);		dataSource.setMaxStatementsPerConnection(20);		dataSource.setMaxStatements(100);		dataSource.setMaxPoolSize(500);		dataSource.setMinPoolSize(5);		return dataSource;	}	@Bean(name = "transactionManager")	@Primary	public JpaTransactionManager jpaTransactionManager() {		JpaTransactionManager transactionManager = new JpaTransactionManager();		transactionManager.setEntityManagerFactory(entityManagerFactoryBean().getObject());		return transactionManager;	}	@Bean(name = "entityManagerFactory")	@Primary	public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean() {		LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();		entityManagerFactoryBean.setJpaVendorAdapter(vendorAdaptor());		entityManagerFactoryBean.setDataSource(dataSource());		entityManagerFactoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);		entityManagerFactoryBean.setPersistenceUnitManager(persistenceUnitManager());		entityManagerFactoryBean.setPersistenceUnitName("orcl");		entityManagerFactoryBean.setPackagesToScan(ENTITYMANAGER_PACKAGES_TO_SCAN);		entityManagerFactoryBean.setJpaProperties(jpaHibernateProperties());		return entityManagerFactoryBean;	}	@Bean	@Primary	public DefaultPersistenceUnitManager persistenceUnitManager() {		DefaultPersistenceUnitManager persistenceUnitManager = new DefaultPersistenceUnitManager();		persistenceUnitManager.setDefaultDataSource(dataSource());		return persistenceUnitManager;	}	private HibernateJpaVendorAdapter vendorAdaptor() {		HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();		vendorAdapter.setDatabasePlatform(env.getProperty(DB_DIALECT));		vendorAdapter.setShowSql(false);		return vendorAdapter;	}	private Properties jpaHibernateProperties() {		Properties properties = new Properties();		properties.put(PROPERTY_NAME_HIBERNATE_FMT_SQL, env.getProperty(PROPERTY_NAME_HIBERNATE_FMT_SQL));		properties.put(PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE, env.getProperty(PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE));		properties.put(PROPERTY_NAME_HIBERNATE_SHOW_SQL, env.getProperty(PROPERTY_NAME_HIBERNATE_SHOW_SQL));		return properties;	}}

这里有几个关键地方：

1. dataSource要加上@Primary注解；

2. entityMananger也要加上@Primary注解；

3. persistenceUnitManager同样也要加上@Primary

次要DataSource源配置：

@Configuration@EnableTransactionManagement@EnableJpaRepositories(		entityManagerFactoryRef = "mysqlEntityManager", 		transactionManagerRef = "mysqlTransactionManager", 		basePackages = "com.opencodez.dao.mysql.repo")public class SecondaryDbConfig {	public static final String PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE = "hibernate.jdbc.batch_size";	public static final String PROPERTY_NAME_HIBERNATE_SHOW_SQL = "hibernate.show_sql";	public static final String PROPERTY_NAME_HIBERNATE_FMT_SQL = "hibernate.format_sql";	public static final String[] ENTITYMANAGER_PACKAGES_TO_SCAN = { "com.opencodez.dao.mysql.domain" };	public static final String DB_URL = "mysql.db.url";	public static final String DB_USER = "mysql.db.user";	public static final String DB_PASSWORD = "mysql.db.password";	public static final String DB_DRIVER = "mysql.db.driver";	public static final String DB_DIALECT = "mysql.db.dialect";	@Autowired	private Environment env;	@Bean	public AnnotationMBeanExporter annotationMBeanExporter() {		AnnotationMBeanExporter annotationMBeanExporter = new AnnotationMBeanExporter();		annotationMBeanExporter.addExcludedBean("dataSource");		annotationMBeanExporter.setRegistrationPolicy(RegistrationPolicy.IGNORE_EXISTING);		return annotationMBeanExporter;	}	@Bean(name = "mysqlDataSource", destroyMethod = "close")	public DataSource dataSource() {		ComboPooledDataSource dataSource = new ComboPooledDataSource();		try {			dataSource.setDriverClass(env.getProperty(DB_DRIVER));		} catch (PropertyVetoException e) {			e.printStackTrace();		}		dataSource.setJdbcUrl(env.getProperty(DB_URL));		dataSource.setUser(env.getProperty(DB_USER));		dataSource.setPassword(env.getProperty(DB_PASSWORD));		dataSource.setAcquireIncrement(5);		dataSource.setMaxStatementsPerConnection(20);		dataSource.setMaxStatements(100);		dataSource.setMaxPoolSize(500);		dataSource.setMinPoolSize(5);		return dataSource;	}	@Bean(name = "mysqlTransactionManager")	public JpaTransactionManager jpaTransactionManager() {		JpaTransactionManager transactionManager = new JpaTransactionManager();		transactionManager.setEntityManagerFactory(entityManagerFactoryBean().getObject());		return transactionManager;	}	@Bean(name = "mysqlEntityManager")	public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean() {		LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();		entityManagerFactoryBean.setJpaVendorAdapter(vendorAdaptor());		entityManagerFactoryBean.setDataSource(dataSource());		entityManagerFactoryBean.setPersistenceProviderClass(HibernatePersistenceProvider.class);		entityManagerFactoryBean.setPersistenceUnitManager(persistenceUnitManager());		entityManagerFactoryBean.setPersistenceUnitName("mysql");		entityManagerFactoryBean.setPackagesToScan(ENTITYMANAGER_PACKAGES_TO_SCAN);				entityManagerFactoryBean.setJpaProperties(jpaHibernateProperties());		return entityManagerFactoryBean;	}	@Bean(name = "mysqlpersistenceUnitManager")	public DefaultPersistenceUnitManager persistenceUnitManager() {		DefaultPersistenceUnitManager persistenceUnitManager = new DefaultPersistenceUnitManager();		persistenceUnitManager.setDefaultDataSource(dataSource());		return persistenceUnitManager;	}	private HibernateJpaVendorAdapter vendorAdaptor() {		HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();		vendorAdapter.setDatabasePlatform(env.getProperty(DB_DIALECT));		vendorAdapter.setShowSql(false);		return vendorAdapter;	}	private Properties jpaHibernateProperties() {		Properties properties = new Properties();		properties.put(PROPERTY_NAME_HIBERNATE_FMT_SQL, env.getProperty(PROPERTY_NAME_HIBERNATE_FMT_SQL));		properties.put(PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE,				env.getProperty(PROPERTY_NAME_HIBERNATE_JDBC_BATCH_SIZE));		properties.put(PROPERTY_NAME_HIBERNATE_SHOW_SQL, env.getProperty(PROPERTY_NAME_HIBERNATE_SHOW_SQL));		return properties;	}}

这里配置类，无需@Primary注解，但是@Bean中的name需要唯一。

这样就完成了数据库的配置，下面定义2个Java类，用于映射数据库表，一个是TblOracle，一个是TblMysql。

TblOracle

@Entity@Table(name = "TBL_ORCL")public class TblOracle {	@Id	@GeneratedValue	@Column(name = "MESSAGE_ID")	private Long id;	@Column(name = "MESSAGE")	private String message;	@Column(name = "CREATED_DATE")	private Date created;	//Getters and Setters}

TblMysql

@Entity@Table(name = "tbl_mysql")public class TblMysql {	@Id	@GeneratedValue	@Column(name = "MESSAGE_ID")	private Long id;	@Column(name = "MESSAGE")	private String message;	@Column(name = "CREATED_DATE")	private Date created;	//Getters and Setters}

对应的persistence.xml如下：

   
   	
    		
     
      com.opencodez.dao.oracle.domain.TblOracle
     		
     
      true
     	
    	
    		
     
      com.opencodez.dao.mysql.domain.TblMysql
     		
     
      true
     	
    
   

在此事例中，定义了相同的controller，这些controller调用了Spring Data JPA中的Repositories。

仓库声明如下：

@Autowiredprivate OracleMessageRepo oracleMessageRepo;@Autowiredprivate MysqlMessageRepo mysqlMessageRepo;

调用如下：

List
   
     messages = oracleMessageRepo.findAll();List
    
      messages = mysqlMessageRepo.findAll();
    
   

上面是使用JPA的方式存储，如果要使用传统的实体管理，需要这样：

@Autowired@Qualifier("entityManagerFactory")private EntityManager oracleEM;	@Autowired@Qualifier("mysqlEntityManager")private EntityManager mysqlEM;

这里需要自己提供检索条件，如下事例：

try {	String sql = "select t from TblOracle t";	Query query = oracleEM.createQuery(sql);	List
   
     list =(List
    
     )query.getResultList( );		} catch (Exception e) {	e.printStackTrace();}try {	String sql = "select t from TblMysql t";	Query query = mysqlEM.createQuery(sql);	List
     
       list=(List
      
       )query.getResultList( );	} catch (Exception e) {	e.printStackTrace();}
      
     
    
   

下面是调用了，运行截图如下：

总结：本次实例展示了如何使用Spring Data JPA轻松配置多源数据库。

创库代码如下：

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