DataSourceAutoConfiguration解析

@Configuration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
//2.1 从配置文件中映射 DataSource 的值
@EnableConfigurationProperties(DataSourceProperties.class)
//2.4/2.5
@Import({ DataSourcePoolMetadataProvidersConfiguration.class,
      DataSourceInitializationConfiguration.class })
public class DataSourceAutoConfiguration {

   //2.2 
   @Configuration
   //判断是否引入 内置数据库：H2，DERBY，HSQL
   @Conditional(EmbeddedDatabaseCondition.class)
   //如果这是没有DataSource/XADataSource 对应的 BeanDefinition，就通过导入 EmbeddedDataSourceConfiguration.class 来，配置内置数据库对应的数据源！！
   @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
   @Import(EmbeddedDataSourceConfiguration.class)
   protected static class EmbeddedDatabaseConfiguration {}

   //2.3 
   @Configuration
   //判断是否引入依赖的数据源：HikariDataSource、tomcat.jdbc.pool.DataSource、BasicDataSource
   @Conditional(PooledDataSourceCondition.class)
   //如果这是没有DataSource/XADataSource 对应的 BeanDefinition，就通过以下属性的配置文件，配置数据源！！
   //配置数据源的时候，如果没有指定一些数据库的参数，就会报错哦
   @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
   @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
         DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class,
         DataSourceJmxConfiguration.class })
   protected static class PooledDataSourceConfiguration {}

   //详细说明见 2.3
   static class PooledDataSourceCondition extends AnyNestedCondition {}
   //详细说明见 2.2
   static class EmbeddedDatabaseCondition extends SpringBootCondition {}