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在实际开发中，有时需要连接多个数据库，例如，一个系统可能需要从不同的数据库中读取和写入数据。Spring 提供了多种方式来配置和管理多数据源，以下将介绍常见的配置和管理方法。
一、多数据源配置
在 Spring 中，可以通过配置多个数据源 Bean，并使用 @Qualifier 注解来区分它们。以下是一个基于 Spring Boot 的多数据源配置示例：
1. 添加依赖
在 Spring Boot 项目的 pom.xml 文件中添加 Spring Data JPA 和数据库驱动的依赖：
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId>
</dependency>
2. 配置文件
在 application.properties 文件中配置多个数据库连接信息：
# 数据源 1 配置
spring.datasource.primary.url=jdbc:mysql://localhost:3306/primarydb?useSSL=false&serverTimezone=UTC
spring.datasource.primary.username=root
spring.datasource.primary.password=password
spring.datasource.primary.driver-class-name=com.mysql.cj.jdbc.Driver# 数据源 2 配置
spring.datasource.secondary.url=jdbc:mysql://localhost:3306/secondarydb?useSSL=false&serverTimezone=UTC
spring.datasource.secondary.username=root
spring.datasource.secondary.password=password
spring.datasource.secondary.driver-class-name=com.mysql.cj.jdbc.Driver
3. 配置类
创建一个配置类，定义多个数据源 Bean：
import org.apache.commons.dbcp2.BasicDataSource;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import javax.sql.DataSource;
import java.util.HashMap;
import java.util.Map;@Configuration
public class DataSourceConfig {@Bean@ConfigurationProperties(prefix = "spring.datasource.primary")public DataSource primaryDataSource() {return new BasicDataSource();}@Bean@ConfigurationProperties(prefix = "spring.datasource.secondary")public DataSource secondaryDataSource() {return new BasicDataSource();}@Bean@Primarypublic LocalContainerEntityManagerFactoryBean primaryEntityManagerFactory(@Qualifier("primaryDataSource") DataSource dataSource) {LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();em.setDataSource(dataSource);em.setPackagesToScan("com.example.primary");em.setJpaVendorAdapter(new HibernateJpaVendorAdapter());em.setJpaProperties(jpaProperties());return em;}@Beanpublic LocalContainerEntityManagerFactoryBean secondaryEntityManagerFactory(@Qualifier("secondaryDataSource") DataSource dataSource) {LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();em.setDataSource(dataSource);em.setPackagesToScan("com.example.secondary");em.setJpaVendorAdapter(new HibernateJpaVendorAdapter());em.setJpaProperties(jpaProperties());return em;}@Beanpublic JpaTransactionManager transactionManager1(@Qualifier("primaryEntityManagerFactory") LocalContainerEntityManagerFactoryBean entityManagerFactory) {JpaTransactionManager transactionManager = new JpaTransactionManager();transactionManager.setEntityManagerFactory(entityManagerFactory.getObject());return transactionManager;}@Beanpublic JpaTransactionManager transactionManager2(@Qualifier("secondaryEntityManagerFactory") LocalContainerEntityManagerFactoryBean entityManagerFactory) {JpaTransactionManager transactionManager = new JpaTransactionManager();transactionManager.setEntityManagerFactory(entityManagerFactory.getObject());return transactionManager;}private Map<String, String> jpaProperties() {Map<String, String> props = new HashMap<>();props.put("hibernate.hbm2ddl.auto", "update");props.put("hibernate.dialect", "org.hibernate.dialect.MySQLDialect");props.put("hibernate.show_sql", "true");return props;}
}
二、多数据源的切换与使用
在实际的业务逻辑中，可以通过注入多个 EntityManager 或 DataSource，并使用 @Qualifier 注解来指定具体使用的数据源。
以下是一个简单的示例，演示如何在业务逻辑层切换使用不同的数据源：
import com.example.primary.domain.User;
import com.example.primary.repository.UserRepository;
import com.example.secondary.domain.Customer;
import com.example.secondary.repository.CustomerRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;@Service
public class UserService {@Autowiredprivate UserRepository userRepository;@Autowiredprivate CustomerRepository customerRepository;@Transactional(transactionManager = "transactionManager1")public void saveUser(User user) {userRepository.save(user);}@Transactional(transactionManager = "transactionManager2")public void saveCustomer(Customer customer) {customerRepository.save(customer);}
}
三、动态数据源切换
在一些复杂的场景下，可能需要动态切换数据源。可以通过实现一个自定义的 AbstractRoutingDataSource 来动态切换数据源。
以下是一个简单的示例：
1. 创建动态数据源上下文
public class DataSourceContextHolder {private static final ThreadLocal<String> contextHolder = new ThreadLocal<>();public static void setDataSource(String dataSource) {contextHolder.set(dataSource);}public static String getDataSource() {return contextHolder.get();}public static void clearDataSource() {contextHolder.remove();}
}
2. 创建动态数据源
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;import javax.sql.DataSource;
import java.util.Map;public class DynamicDataSource extends AbstractRoutingDataSource {@Overrideprotected Object determineCurrentLookupKey() {return DataSourceContextHolder.getDataSource();}
}
3. 配置动态数据源
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternUtils;
import org.springframework.jdbc.datasource.init.DataSourceInitializer;
import org.springframework.jdbc.datasource.init.DatabasePopulator;
import org.springframework.jdbc.datasource.init.ResourceDatabasePopulator;
import javax.sql.DataSource;
import java.io.IOException;@Configuration
public class DataSourceConfig {@Bean@ConfigurationProperties(prefix = "spring.datasource.primary")public DataSource primaryDataSource() throws IOException {return dataSource("primary");}@Bean@ConfigurationProperties(prefix = "spring.datasource.secondary")public DataSource secondaryDataSource() throws IOException {return dataSource("secondary");}private DataSource dataSource(String schema) throws IOException {HikariDataSource dataSource = new HikariDataSource();dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/" + schema + "?useSSL=false&serverTimezone=UTC");dataSource.setUsername("root");dataSource.setPassword("password");dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");dataSource.setMaximumPoolSize(5);dataSource.setMinimumIdle(1);dataSource.setIdleTimeout(30000);dataSource.setConnectionTimeout(30000);dataSource.setMaxLifetime(600000);ResourcePatternResolver resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(resourceLoader);ResourceDatabasePopulator resourceDatabasePopulator = new ResourceDatabasePopulator();resourceDatabasePopulator.addScript(resourcePatternResolver.getResource("classpath:schema.sql"));resourceDatabasePopulator.addScript(resourcePatternResolver.getResource("classpath:test-data.sql"));DataSourceInitializer dataSourceInitializer = new DataSourceInitializer();dataSourceInitializer.setDataSource(dataSource);dataSourceInitializer.setDatabasePopulator(resourceDatabasePopulator);dataSourceInitializer.setEnabled(true);dataSourceInitializer.afterPropertiesSet();return dataSource;}@Beanpublic DynamicDataSource dataSource(@Qualifier("primaryDataSource") DataSource primaryDataSource,@Qualifier("secondaryDataSource") DataSource secondaryDataSource) {DynamicDataSource dynamicDataSource = new DynamicDataSource();Map<Object, Object> dataSourceMap = new HashMap<>();dataSourceMap.put("primary", primaryDataSource);dataSourceMap.put("secondary", secondaryDataSource);dynamicDataSource.setTargetDataSources(dataSourceMap);dynamicDataSource.setDefaultTargetDataSource(primaryDataSource);return dynamicDataSource;}
}
总结
Spring 提供了多种配置和管理多数据源的方式，可以根据项目的实际需求灵活选择。在需要切换数据源的场景下，可以通过配置多个数据源 Bean 并使用 @Qualifier 注解来指定具体使用的数据源。对于更复杂的动态数据源切换场景，可以自定义 AbstractRoutingDataSource 来实现动态切换。掌握多数据源的配置与管理，有助于构建更加灵活、高效的后端应用。