你可以用 AbstractRoutingDataSource 为了达到这个目的。 AbstractRoutingDataSource 需要信息来知道 DataSource 路由到（称为上下文），由 determineCurrentLookupKey() 方法。用这里的例子。
定义上下文如下：

public enum ClientDatabase {
    CLIENT_A, CLIENT_B
}

然后您需要定义将在中使用的上下文持有者 determineCurrentLookupKey() ```
public class ClientDatabaseContextHolder {

private static ThreadLocal<ClientDatabase> CONTEXT = new ThreadLocal<>();

public static void set(ClientDatabase clientDatabase) {
    Assert.notNull(clientDatabase, "clientDatabase cannot be null");
    CONTEXT.set(clientDatabase);
}

public static ClientDatabase getClientDatabase() {
    return CONTEXT.get();
}

public static void clear() {
    CONTEXT.remove();
}

}

然后你可以延伸 `AbstractRoutingDataSource` 如下所示：

public class ClientDataSourceRouter extends AbstractRoutingDataSource {

@Override
protected Object determineCurrentLookupKey() {
    return ClientDatabaseContextHolder.getClientDatabase();
}

}

最后， `DataSource` bean配置：

@Bean
public DataSource clientDatasource() {
Map<Object, Object> targetDataSources = new HashMap<>();
DataSource clientADatasource = clientADatasource();
DataSource clientBDatasource = clientBDatasource();
targetDataSources.put(ClientDatabase.CLIENT_A,
clientADatasource);
targetDataSources.put(ClientDatabase.CLIENT_B,
clientBDatasource);

ClientDataSourceRouter clientRoutingDatasource 
  = new ClientDataSourceRouter();
clientRoutingDatasource.setTargetDataSources(targetDataSources);
clientRoutingDatasource.setDefaultTargetDataSource(clientADatasource);
return clientRoutingDatasource;

}

https://github.com/wmeints/spring-multi-tenant-demo
按照这个逻辑，我现在可以解决了。有些版本需要升级，代码也需要升级。
Spring 启动版本已更改。
org.springframework.boot spring boot starter父版本2.1.0.release
mysql版本已被删除。
还有一些小的变化 MultitenantConfiguration.java ```
@Configuration
public class MultitenantConfiguration {

@Autowired
private DataSourceProperties properties;

/**

• Defines the data source for the application

• @return
  */
  @Bean
  @ConfigurationProperties(
  prefix = "spring.datasource"
  )
  public DataSource dataSource() {
  File[] files = Paths.get("tenants").toFile().listFiles();
  Map<Object,Object> resolvedDataSources = new HashMap<>();

  if(files != null) {
  for (File propertyFile : files) {
  Properties tenantProperties = new Properties();
  DataSourceBuilder dataSourceBuilder = DataSourceBuilder.create(this.getClass().getClassLoader());

       try {
           tenantProperties.load(new FileInputStream(propertyFile));
  
           String tenantId = tenantProperties.getProperty("name");
  
           dataSourceBuilder.driverClassName(properties.getDriverClassName())
                   .url(tenantProperties.getProperty("datasource.url"))
                   .username(tenantProperties.getProperty("datasource.username"))
                   .password(tenantProperties.getProperty("datasource.password"));
  
           if (properties.getType() != null) {
               dataSourceBuilder.type(properties.getType());
           }
  
           resolvedDataSources.put(tenantId, dataSourceBuilder.build());
       } catch (IOException e) {
           e.printStackTrace();
  
           return null;
       }
   }

  }

  // Create the final multi-tenant source.
  // It needs a default database to connect to.
  // Make sure that the default database is actually an empty tenant database.
  // Don't use that for a regular tenant if you want things to be safe!
  MultitenantDataSource dataSource = new MultitenantDataSource();
  dataSource.setDefaultTargetDataSource(defaultDataSource());
  dataSource.setTargetDataSources(resolvedDataSources);

  // Call this to finalize the initialization of the data source.
  dataSource.afterPropertiesSet();

  return dataSource;
  }

/**

• Creates the default data source for the application

• @return
  */
  private DataSource defaultDataSource() {
  DataSourceBuilder dataSourceBuilder = DataSourceBuilder.create(this.getClass().getClassLoader())
  .driverClassName(properties.getDriverClassName())
  .url(properties.getUrl())
  .username(properties.getUsername())
  .password(properties.getPassword());

  if(properties.getType() != null) {
  dataSourceBuilder.type(properties.getType());
  }

  return dataSourceBuilder.build();
  }

}
这种变化是由于 `DataSourceBuilder` 已移动到另一个路径，并且其构造函数已更改。
还更改了中的mysql驱动程序类名 `application.properties` 这样地
spring.datasource.driver类名=com.mysql.jdbc.driver