Springcloud+Mybatis使用多数据源的四种方式(小结)

当我们使用SpringCloud和Mybatis时，有时需要使用多数据源来访问不同的数据库。下面介绍四种实现方式。

方式一：使用Mybatis-Plus

Mybatis-Plus 是一个 MyBatis 的增强工具，提供了许多方便的功能，其中就包括多数据源的支持。

1. 引入 mybatis-plus-boot-starter 依赖

xml
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>${mybatis-plus.version}</version>
</dependency>

需要设置 mybatis-plus.mapper-locations 属性，指定 mapper 文件的位置:

properties
mybatis-plus.mapper-locations=classpath:/mapper/**/*Mapper.xml

1. 配置多数据源

application.yml

yaml
spring:
datasource:
dynamic:
primary: master
datasource:
master:
url: jdbc:mysql://localhost:3306/master?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver
slave:
url: jdbc:mysql://localhost:3306/slave?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver

1. 使用注解配置数据源和事务

```java
@Service
public class UserServiceImpl implements UserService {

   @Autowired
   private UserMapper userMapper;

   @Override
   @DataSource("master")
   @Transactional(rollbackFor = Exception.class)
   public void addUser(User user) {
       userMapper.insert(user);
   }

   @Override
   @DataSource("slave")
   public List<User> findAllUsers() {
       return userMapper.selectList(null);
   }

}
```

@DataSource 是自定义注解，用来指定数据源，实现如下:

java
@Target({ElementType.METHOD,ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface DataSource {
String value() default "master";
}

方式二：使用 aop 和 ThreadLocal 实现多数据源

1. 创建数据源配置类，动态获取数据源

```java
public class DynamicDataSource extends AbstractRoutingDataSource {

   @Override
   protected Object determineCurrentLookupKey() {
       return DynamicDataSourceContextHolder.getDataSourceKey();
   }

}
```

1. 创建数据源上下文类，存储当前线程的数据源 key

```java
public class DynamicDataSourceContextHolder {

   private static final ThreadLocal<String> contextHolder = new ThreadLocal<>();

   public static void setDataSourceKey(String dataSourceKey) {
       contextHolder.set(dataSourceKey);
   }

   public static String getDataSourceKey() {
       return contextHolder.get();
   }

   public static void clearDataSourceKey() {
       contextHolder.remove();
   }

}
```

1. 在切面中拦截指定方法，根据方法名称判断数据源

```java
@Slf4j
@Aspect
@Component
public class DataSourceAspect {

   @Pointcut("execution(* com.example.demo.service.*.*(..))")
   private void serviceAspect() {
   }

   @Before("serviceAspect()")
   public void before(JoinPoint joinPoint) {
       String methodName = joinPoint.getSignature().getName();
       if (methodName.startsWith("get")) {
            DynamicDataSourceContextHolder.setDataSourceKey("slave");
       } else {
            DynamicDataSourceContextHolder.setDataSourceKey("master");
       }
       log.info("data source switch to [{}]", DynamicDataSourceContextHolder.getDataSourceKey());
   }

   @After("serviceAspect()")
   public void after() {
       DynamicDataSourceContextHolder.clearDataSourceKey();
       log.info("data source cleared");
   }

}
```

方式三：使用 JdbcTemplate

1. 在配置文件中定义数据源

yaml
spring:
datasource:
master:
url: jdbc:mysql://localhost:3306/master?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver
slave:
url: jdbc:mysql://localhost:3306/slave?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver

1. 在代码中使用 JdbcTemplate 访问数据

```java
@Service
public class UserServiceImpl implements UserService {

   @Autowired
   @Qualifier("masterJdbcTemplate")
   private JdbcTemplate masterJdbcTemplate;

   @Autowired
   @Qualifier("slaveJdbcTemplate")
   private JdbcTemplate slaveJdbcTemplate;

   @Override
   public void addUser(User user) {
       masterJdbcTemplate.update("INSERT INTO user(id, name) VALUES (?,?)", user.getId(), user.getName());
   }

   @Override
   public List<User> findAllUsers() {
       return slaveJdbcTemplate.query("SELECT * FROM user", new BeanPropertyRowMapper<>(User.class));
   }

}
```

DataSource 的配置类:

```java
@Configuration
public class DataSourceConfig {

   @Bean(name = "masterDataSource")
   @ConfigurationProperties(prefix = "spring.datasource.master")
   public DataSource masterDataSource() {
       return DataSourceBuilder.create().build();
   }

   @Bean(name = "slaveDataSource")
   @ConfigurationProperties(prefix = "spring.datasource.slave")
   public DataSource slaveDataSource() {
       return DataSourceBuilder.create().build();
   }

   @Bean(name = "masterJdbcTemplate")
   public JdbcTemplate masterJdbcTemplate(@Qualifier("masterDataSource") DataSource dataSource) {
       return new JdbcTemplate(dataSource);
   }

   @Bean(name = "slaveJdbcTemplate")
   public JdbcTemplate slaveJdbcTemplate(@Qualifier("slaveDataSource") DataSource dataSource) {
       return new JdbcTemplate(dataSource);
   }

}
```

方式四：使用 SqlSessionFactory

1. 在配置文件中定义数据源

yaml
spring:
datasource:
master:
url: jdbc:mysql://localhost:3306/master?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver
slave:
url: jdbc:mysql://localhost:3306/slave?characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver

1. 创建数据源工厂

```java
@Configuration
public class DataSourceConfig {

   @Bean(name = "masterDataSource")
   @ConfigurationProperties(prefix = "spring.datasource.master")
   public DataSource masterDataSource() {
       return DataSourceBuilder.create().build();
   }

   @Bean(name = "slaveDataSource")
   @ConfigurationProperties(prefix = "spring.datasource.slave")
   public DataSource slaveDataSource() {
       return DataSourceBuilder.create().build();
   }

   @Bean(name = "dynamicDataSource")
   public DataSource dynamicDataSource(@Qualifier("masterDataSource") DataSource masterDataSource,
                                        @Qualifier("slaveDataSource") DataSource slaveDataSource) {
       Map<Object, Object> targetDataSources = new HashMap<>();
       targetDataSources.put("master", masterDataSource);
       targetDataSources.put("slave", slaveDataSource);
       DynamicDataSource dataSource = new DynamicDataSource();
       dataSource.setTargetDataSources(targetDataSources);
       dataSource.setDefaultTargetDataSource(masterDataSource);
       return dataSource;
   }

   @Bean(name = "masterSqlSessionFactory")
   @Primary
   public SqlSessionFactory masterSqlSessionFactory(@Qualifier("masterDataSource") DataSource dataSource)
           throws Exception {
       SqlSessionFactoryBean sessionFactoryBean = new SqlSessionFactoryBean();
       sessionFactoryBean.setDataSource(dataSource);
       sessionFactoryBean.setMapperLocations(
               new PathMatchingResourcePatternResolver().getResource("classpath*:mapper/*/*Mapper.xml"));
       return sessionFactoryBean.getObject();
   }

   @Bean(name = "slaveSqlSessionFactory")
   public SqlSessionFactory slaveSqlSessionFactory(@Qualifier("slaveDataSource") DataSource dataSource)
           throws Exception {
       SqlSessionFactoryBean sessionFactoryBean = new SqlSessionFactoryBean();
       sessionFactoryBean.setDataSource(dataSource);
       sessionFactoryBean.setMapperLocations(
               new PathMatchingResourcePatternResolver().getResource("classpath*:mapper/*/*Mapper.xml"));
       return sessionFactoryBean.getObject();
   }

   @Bean(name = "masterTransactionManager")
   @Primary
   public DataSourceTransactionManager masterTransactionManager(@Qualifier("masterDataSource") DataSource dataSource) {
       return new DataSourceTransactionManager(dataSource);
   }

   @Bean(name = "slaveTransactionManager")
   public DataSourceTransactionManager slaveTransactionManager(@Qualifier("slaveDataSource") DataSource dataSource) {
       return new DataSourceTransactionManager(dataSource);
   }

}
```

1. 在代码中指定数据源

```java
@Service
public class UserServiceImpl implements UserService {

   @Autowired
   @Qualifier("masterSqlSessionFactory")
   private SqlSessionFactory masterSqlSessionFactory;

   @Autowired
   @Qualifier("slaveSqlSessionFactory")
   private SqlSessionFactory slaveSqlSessionFactory;

   @Override
   public void addUser(User user) {
       SqlSession sqlSession = SqlSessionUtils.getSqlSession(masterSqlSessionFactory);
       UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
       userMapper.insert(user);
       sqlSession.commit();
       SqlSessionUtils.closeSqlSession(sqlSession, masterSqlSessionFactory);
   }

   @Override
   public List<User> findAllUsers() {
       SqlSession sqlSession = SqlSessionUtils.getSqlSession(slaveSqlSessionFactory);
       UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
       List<User> users = userMapper.selectAll();
       SqlSessionUtils.closeSqlSession(sqlSession, slaveSqlSessionFactory);
       return users;
   }

}
```

以上就是四种使用 SpringCloud 和 Mybatis 实现多数据源的方法，按照自己的场景选择适合的方法即可。

下面是示例代码：

1. SpringCloud-Mybatis-Plus
2. SpringCloud-MultipleDataSource