1.概述
项目中经常会遇到一个应用需要访问多个数据源的情况，本文介绍在SpringBoot项目中利用SpringDataJpa技术如何支持多个数据库的数据源。
具体的代码参照该 示例项目
2.建立实体类（Entity）
首先，我们创建两个简单的实体类，分别属于两个不同的数据源，用于演示多数据源数据的保存和查询。
Test实体类：
package com.example.demo.test.data; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name = "test") public class Test { @Id private Integer id; public Test(){ } public Integer getId() { return this.id; } public void setId(Integer id){ this.id = id; } }
Other实体类：
package com.example.demo.other.data; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name = "other") public class Other { @Id private Integer id; public Integer getId() { return this.id; } public void setId(Integer id){ this.id = id; } }
需要注意的是，这两个实体类分属于不同的package，这一点极为重要，spring会根据实体类所属的package来决定用那一个数据源进行操作。
3.建立Repository
分别建立两个实体类对应的Repository，用于进行数据操作。
TestRepository:
package com.example.demo.test.data; import org.springframework.data.jpa.repository.JpaRepository; public interface TestRepository extends JpaRepository<Test, Integer> { }
OtherRepository:
package com.example.demo.other.data; import org.springframework.data.jpa.repository.JpaRepository; public interface OtherRepository extends JpaRepository<Other, Integer> { }
得益于spring-data-jpa优秀的封装，我们只需创建一个接口，就拥有了对实体类的操作能力。
3.对多数据源进行配置
分别对Test和Other两个实体类配置对应的数据源。配置的内容主要包含三个要素：
- dataSource，数据源的连接信息
- entityManagerFactory，数据处理
- transactionManager，事务管理
Test实体类的数据源配置 TestDataConfig：
package com.example.demo.config; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder; import org.springframework.boot.autoconfigure.orm.jpa.JpaProperties; import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Primary; import org.springframework.data.jpa.repository.config.EnableJpaRepositories; import org.springframework.orm.jpa.JpaTransactionManager; import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean; import org.springframework.transaction.PlatformTransactionManager; import org.springframework.transaction.annotation.EnableTransactionManagement; import javax.persistence.EntityManagerFactory; import javax.sql.DataSource; @Configuration @EnableTransactionManagement @EnableJpaRepositories( entityManagerFactoryRef = "entityManagerFactory", basePackages = {"com.example.demo.test.data"} ) public class TestDataConfig { @Autowired private JpaProperties jpaProperties; @Primary @Bean(name = "dataSource") @ConfigurationProperties(prefix = "spring.datasource") public DataSource dataSource() { return DataSourceBuilder.create().build(); } @Primary @Bean(name = "entityManagerFactory") public LocalContainerEntityManagerFactoryBean entityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier("dataSource") DataSource dataSource) { return builder .dataSource(dataSource) .packages("com.example.demo.test.data") .properties(jpaProperties.getHibernateProperties(dataSource)) .persistenceUnit("test") .build(); } @Primary @Bean(name = "transactionManager") public PlatformTransactionManager transactionManager( @Qualifier("entityManagerFactory") EntityManagerFactory entityManagerFactory) { return new JpaTransactionManager(entityManagerFactory); } }
代码中的Primary注解表示这是默认数据源。
Other实体类的数据源配置 OtherDataConfig：
package com.example.demo.config; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder; import org.springframework.boot.autoconfigure.orm.jpa.JpaProperties; import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.data.jpa.repository.config.EnableJpaRepositories; import org.springframework.orm.jpa.JpaTransactionManager; import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean; import org.springframework.transaction.PlatformTransactionManager; import org.springframework.transaction.annotation.EnableTransactionManagement; import javax.persistence.EntityManagerFactory; import javax.sql.DataSource; @Configuration @EnableTransactionManagement @EnableJpaRepositories( entityManagerFactoryRef = "otherEntityManagerFactory", transactionManagerRef = "otherTransactionManager", basePackages = {"com.example.demo.other.data"} ) public class OtherDataConfig { @Autowired private JpaProperties jpaProperties; @Bean(name = "otherDataSource") @ConfigurationProperties(prefix = "other.datasource") public DataSource otherDataSource() { return DataSourceBuilder.create().build(); } @Bean(name = "otherEntityManagerFactory") public LocalContainerEntityManagerFactoryBean otherEntityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier("otherDataSource") DataSource otherDataSource) { return builder .dataSource(otherDataSource) .packages("com.example.demo.other.data") .properties(jpaProperties.getHibernateProperties(otherDataSource)) .persistenceUnit("other") .build(); } @Bean(name = "otherTransactionManager") public PlatformTransactionManager otherTransactionManager( @Qualifier("otherEntityManagerFactory") EntityManagerFactory otherEntityManagerFactory) { return new JpaTransactionManager(otherEntityManagerFactory); } }
3.数据操作
我们创建一个Service类TestService来分别对两个数据源进行数据的操作。
package com.example.demo.service; import com.example.demo.other.data.Other; import com.example.demo.other.data.OtherRepository; import com.example.demo.test.data.Test; import com.example.demo.test.data.TestRepository; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component; @Component public class TestService { @Autowired private TestRepository testRepository; @Autowired private OtherRepository otherRepository; @Value("${name:World}") private String name; public String getHelloMessage() { Test test = new Test(); test.setId(1); test = testRepository.save(test); Other other = new Other(); other.setId(2); other = otherRepository.save(other); return "Hello " + this.name + " : test's value = " + test.getId() + " , other's value = " + other.getId(); } }
对Test和Other分别进行数据插入和读取操作，程序运行后会打印出两个数据源各自的数据。 数据库采用的mysql，连接信息在application.yml进行配置。
spring: datasource: url: jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&useSSL=false testWhileIdle: true validationQuery: SELECT 1 from dual username: test password: 11111111 driverClassName: com.mysql.jdbc.Driver jpa: database: MYSQL show-sql: true hibernate: show-sql: true ddl-auto: create naming-strategy: org.hibernate.cfg.ImprovedNamingStrategy properties: hibernate.dialect: org.hibernate.dialect.MySQL5Dialect other: datasource: url: jdbc:mysql://localhost:3306/other?characterEncoding=utf-8&useSSL=false testWhileIdle: true validationQuery: SELECT 1 username: other password: 11111111 driverClassName: com.mysql.jdbc.Driver jpa: database: MYSQL show-sql: true hibernate: show-sql: true ddl-auto: create naming-strategy: org.hibernate.cfg.ImprovedNamingStrategy properties: hibernate.dialect: org.hibernate.dialect.MySQL5Dialect
Test实体对应的是主数据源，采用了spring-boot的默认数据源配置项，Other实体单独配置数据源连接。具体应该读取哪一段配置内容，是在配置类OtherDataConfig中这行代码指定的。
@ConfigurationProperties(prefix = "other.datasource")
本示例需要建立的数据库用户和库可以通过以下命令处理：
CREATE USER 'test'@'localhost' IDENTIFIED BY '11111111'; GRANT ALL PRIVILEGES ON *.* TO 'test'@'localhost'; CREATE USER 'other'@'localhost' IDENTIFIED BY '11111111'; GRANT ALL PRIVILEGES ON *.* TO 'other'@'localhost'; create database test; create database other;
4.总结
spring-data-jpa极大的简化了数据库操作，对于多数据源的支持，也只是需要增加一下配置文件和配置类而已。其中的关键内容有3点：
-
配置文件中数据源的配置
-
配置类的编写
-
实体类所在的package必须与配置类中指定的package一致，如OtherDataConfig中指定的basePackages = {"com.example.demo.other.data"}
