Spring多数据源实现的方式大概有2中,一种是新建多个MapperScan扫描不同包,另外一种则是通过继承AbstractRoutingDataSource实现动态路由。今天作者主要基于后者做的实现,且方式1的实现比较简单这里不做过多探讨。
方式1的实现(核心代码):
@Configuration @MapperScan(basePackages = "com.goofly.test1", sqlSessionTemplateRef = "test1SqlSessionTemplate") public class DataSource1Config1 { @Bean(name = "dataSource1") @ConfigurationProperties(prefix = "spring.datasource.test1") @Primary public DataSource testDataSource() { return DataSourceBuilder.create().build(); } // .....略 } @Configuration @MapperScan(basePackages = "com.goofly.test2", sqlSessionTemplateRef = "test1SqlSessionTemplate") public class DataSourceConfig2 { @Bean(name = "dataSource2") @ConfigurationProperties(prefix = "spring.datasource.test2") @Primary public DataSource testDataSource() { return DataSourceBuilder.create().build(); } // .....略 }
方式2的实现(核心代码):
public class DynamicRoutingDataSource extends AbstractRoutingDataSource { private static final Logger log = Logger.getLogger(DynamicRoutingDataSource.class); @Override protected Object determineCurrentLookupKey() { //从ThreadLocal中取值 return DynamicDataSourceContextHolder.get(); } }
第1种方式虽然实现比较加单,劣势就是不同数据源的mapper文件不能在同一包名,就显得不太灵活了。所以为了更加灵活的作为一个组件的存在,作者采用的第二种方式实现。
- 当请求经过被注解修饰的类后,此时会进入到切面逻辑中。
- 切面逻辑会获取注解中设置的key值,然后将该值存入到
ThreadLocal中 - 执行完切面逻辑后,会执行
AbstractRoutingDataSource.determineCurrentLookupKey()方法,然后从ThreadLocal中获取之前设置的key值,然后将该值返回。 - 由于
AbstractRoutingDataSource的targetDataSources是一个map,保存了数据源key和数据源的对应关系,所以能够顺利的找到该对应的数据源。
org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource,如下:
public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean { private Map<Object, Object> targetDataSources; private Object defaultTargetDataSource; private boolean lenientFallback = true; private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup(); private Map<Object, DataSource> resolvedDataSources; private DataSource resolvedDefaultDataSource; protected DataSource determineTargetDataSource() { Assert.notNull(this.resolvedDataSources, "DataSource router not initialized"); Object lookupKey = determineCurrentLookupKey(); DataSource dataSource = this.resolvedDataSources.get(lookupKey); if (dataSource == null && (this.lenientFallback || lookupKey == null)) { dataSource = this.resolvedDefaultDataSource; } if (dataSource == null) { throw new IllegalStateException("Cannot determine target DataSource for lookup key [" + lookupKey + "]"); } return dataSource; } /** * Determine the current lookup key. This will typically be * implemented to check a thread-bound transaction context. * <p>Allows for arbitrary keys. The returned key needs * to match the stored lookup key type, as resolved by the * {@link #resolveSpecifiedLookupKey} method. */ protected abstract Object determineCurrentLookupKey(); //........略
targetDataSources是一个map结构,保存了key与数据源的对应关系;
dataSourceLookup是一个DataSourceLookup类型,默认实现是JndiDataSourceLookup。点开该类源码会发现,它实现了通过key获取DataSource的逻辑。当然,这里可以通过setDataSourceLookup()来改变其属性,因为关于此处有一个坑,后面会讲到。
public class JndiDataSourceLookup extends JndiLocatorSupport implements DataSourceLookup { public JndiDataSourceLookup() { setResourceRef(true); } @Override public DataSource getDataSource(String dataSourceName) throws DataSourceLookupFailureException { try { return lookup(dataSourceName, DataSource.class); } catch (NamingException ex) { throw new DataSourceLookupFailureException( "Failed to look up JNDI DataSource with name '" + dataSourceName + "'", ex); } } }
多数据源
### 多数据源 ``` # db1 spring.datasource.master.url = jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false spring.datasource.master.username = root spring.datasource.master.password = 123456 spring.datasource.master.driverClassName = com.mysql.jdbc.Driver spring.datasource.master.validationQuery = true spring.datasource.master.testOnBorrow = true ## db2 spring.datasource.slave.url = jdbc:mysql://127.0.0.1:3306/test1?useUnicode=true&characterEncoding=utf8&useSSL=false spring.datasource.slave.username = root spring.datasource.slave.password = 123456 spring.datasource.slave.driverClassName = com.mysql.jdbc.Driver spring.datasource.slave.validationQuery = true spring.datasource.slave.testOnBorrow = true #主数据源名称 spring.maindb=master #mapperper包路径 mapper.basePackages =com.btps.xli.multidb.demo.mapper ```
单数据源
为了让使用者能够用最小的改动实现最好的效果,作者对单数据源的多种配置做了兼容。
配置1:
spring.datasource.master.url = jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false spring.datasource.master.username = root spring.datasource.master.password = 123456 spring.datasource.master.driverClassName = com.mysql.jdbc.Driver spring.datasource.master.validationQuery = true spring.datasource.master.testOnBorrow = true # mapper包路径 mapper.basePackages = com.goofly.xli.multidb.demo.mapper # 主数据源名称 spring.maindb=master
配置2
spring.datasource.url = jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false spring.datasource.username = root spring.datasource.password = 123456 spring.datasource.driverClassName = com.mysql.jdbc.Driver spring.datasource.validationQuery = true spring.datasource.testOnBorrow = true # mapper包路径 mapper.basePackages = com.goofly.xli.multidb.demo.mapper
Description: The dependencies of some of the beans in the application context form a cycle: happinessController (field private com.db.service.HappinessService com.db.controller.HappinessController.happinessService) ↓ happinessServiceImpl (field private com.db.mapper.MasterDao com.db.service.HappinessServiceImpl.masterDao) ↓ masterDao defined in file [E:\GitRepository\framework-gray\test-db\target\classes\com\db\mapper\MasterDao.class] ↓ sqlSessionFactory defined in class path resource [com/goofly/xli/datasource/core/DynamicDataSourceConfiguration.class] ┌─────┐ | dynamicDataSource defined in class path resource [com/goofly/xli/datasource/core/DynamicDataSourceConfiguration.class] ↑ ↓ | firstDataSource defined in class path resource [com/goofly/xli/datasource/core/DynamicDataSourceConfiguration.class] ↑ ↓ | dataSourceInitializer
解决方案:
在Spring boot启动的时候排除DataSourceAutoConfiguration即可。如下:
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class}) public class DBMain { public static void main(String[] args) { SpringApplication.run(DBMain.class, args); } }
但是作者在创建多数据源的时候由于并未创建多个
DataSource的Bean,而是只创建了一个即需要做动态数据源的那个Bean。 其他的DataSource则直接创建实例然后存放在Map里面,然后再设置到DynamicRoutingDataSource#setTargetDataSources即可。因此这种方式也不会出现循环依赖的问题!
笔者在设计之初是想构建一个动态刷新数据源的方案,所以利用了
SpringCloud的@RefreshScope去标注数据源,然后利用RefreshScope#refresh实现刷新。但是在实验的时候发现由Druid创建的数据源会因此而关闭,由Spring的DataSourceBuilder创建的数据源则不会发生任何变化。 最后关于此也没能找到解决方案。同时思考,如果只能的可以实现动态刷新的话,那么数据源的原有连接会因为刷新而中断吗还是会有其他处理?
有这么一种特殊情况,一个事务中调用了两个不同数据源,这个时候动态切换数据源会因此而失效。
翻阅了很多文章,大概找了2中解决方案,一种是Atomikos进行事务管理,但是貌似性能并不是很理想。
另外一种则是通过优先级控制,切面的的优先级必须要大于数据源的优先级,用注解
@Order控制。此处留一个坑!