自定义注解有几点需要注意：

1）@Target 是作用的目标，接口、方法、类、字段、包等等，具体看：ElementType

2）@Retention 是注解存在的范围，RUNTIME代表的是注解会在class字节码文件中存在，在运行时可以通过反射获取到，具体看：RetentionPolicy

3）允许的变量，通常都要给定默认值，比如我们使用一个service时，可以@Service，也可以

@Service("xxxx")
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD
})
public @interface RoutingDataSource {String value() default DataSources.MASTER_DB;
}

## datasource master #
spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/master?characterEncoding=UTF-8
spring.datasource.username=root
spring.datasource.password=466420182## datasource slave #
spring.datasourceSlave.type=com.alibaba.druid.pool.DruidDataSource
spring.datasourceSlave.driver-class-name=com.mysql.jdbc.Driver
spring.datasourceSlave.url=jdbc:mysql://localhost:3306/slave?characterEncoding=UTF-8
spring.datasourceSlave.username=root
spring.datasourceSlave.password=466420182

public interface DataSources {String MASTER_DB = "masterDB";String SLAVE_DB = "slaveDB";
}

@Configuration
public class DatasourceConfig {//destroy-method="close"的作用是当数据库连接不使用的时候,就把该连接重新放到数据池中,方便下次使用调用.@Bean(destroyMethod =  "close", name = DataSources.MASTER_DB)@ConfigurationProperties(prefix = "spring.datasource")public DataSource dataSource() {return DataSourceBuilder.create().type(DruidDataSource.class).build();}@Bean(destroyMethod =  "close", name = DataSources.SLAVE_DB)@ConfigurationProperties(prefix = "spring.datasourceSlave")public DataSource dataSourceSlave() {return DataSourceBuilder.create().type(DruidDataSource.class).build();}
}

@Configuration
@MapperScan(basePackages = {"com.xxx.dao"})  // 这里需要替换为实际的路径
public class MybatisConfig {@Autowired@Qualifier(Datasources.MASTER_DB)private DataSource masterDB;@Autowired@Qualifier(DataSources.SLAVE_DB)private DataSource slaveDB;/*** 动态数据源*/@Bean(name = "dynamicDataSource")public DataSource dynamicDataSource() {DynamicDataSource dynamicDataSource = new DynamicDataSource();// 默认数据源
        dynamicDataSource.setDefaultTargetDataSource(masterDB);// 配置多数据源Map<Object, Object> dsMap = Maps.newHashMap();dsMap.put(DataSources.MASTER_DB, masterDB);dsMap.put(DataSources.SLAVE_DB, slaveDB);dynamicDataSource.setTargetDataSources(dsMap);return dynamicDataSource;}@Bean@ConfigurationProperties(prefix = "mybatis")public SqlSessionFactoryBean sqlSessionFactoryBean() {SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();// 配置数据源，此处配置为关键配置，如果没有将 dynamicDataSource 作为数据源则不能实现切换
        sqlSessionFactoryBean.setDataSource(dynamicDataSource());return sqlSessionFactoryBean;}
}

@Slf4j
public class DataSourceContextHolder {/*** 默认数据源*/public static final String DEFAULT_DATASOURCE = DataSources.MASTER_DB;private static final ThreadLocal<String> contextHolder = new ThreadLocal<>();// 设置数据源名public static void setDB(String dbType) {log.debug("切换到{}数据源", dbType);contextHolder.set(dbType);}// 获取数据源名public static String getDB() {return (contextHolder.get());}// 清除数据源名public static void clearDB() {contextHolder.remove();}
}

@Aspect
@Component
@Slf4j
public class DynamicDataSourceAspect {@Before("@annotation(RoutingDataSource)")public void beforeSwitchDS(JoinPoint point){//获得当前访问的classClass<?> className = point.getTarget().getClass();//获得访问的方法名String methodName = point.getSignature().getName();//得到方法的参数的类型Class[] argClass = ((MethodSignature)point.getSignature()).getParameterTypes();String dataSource = DataSourceContextHolder.DEFAULT_DATASOURCE;try {// 得到访问的方法对象Method method = className.getMethod(methodName, argClass);// 判断是否存在@DS注解if (method.isAnnotationPresent(RoutingDataSource.class)) {RoutingDataSource annotation = method.getAnnotation(RoutingDataSource.class);// 取出注解中的数据源名dataSource = annotation.value();}} catch (Exception e) {log.error("routing datasource exception, " + methodName, e);}// 切换数据源
        DataSourceContextHolder.setDB(dataSource);}@After("@annotation(RoutingDataSource)")public void afterSwitchDS(JoinPoint point){DataSourceContextHolder.clearDB();}
}

五、动态的取出我们在切面里设置的数据源的字符串即可

@Slf4j
public class DynamicDataSource extends AbstractRoutingDataSource {@Overrideprotected Object determineCurrentLookupKey() {log.debug("数据源为{}", DataSourceContextHolder.getDB());return DataSourceContextHolder.getDB();}
}

@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class
})

@Service
public class DataSourceRoutingService {@Resourceprivate SysUserMapper sysUserMapper;@RoutingDataSource(DataSources.MASTER_DB) // 这个注解这时是可以省略，因为默认就是访问主库public SysUser test1(int id) {return sysUserMapper.selectByPrimaryKey(id);}@RoutingDataSource(DataSources.SLAVE_DB)public SysUser test2(int id) {return sysUserMapper.selectByPrimaryKey(id);}
}