Functions of JDBCServer

JDBCServer is a JDBC interface. Users can use JDBC to connect to JDBCServer to access SparkSQL data. When JDBCServer is started, a SparkSQL application is started, and the clients connected through JDBC can share the resources of the SparkSQL application, that is, different users can share data. When the JDBCServer is started, a listener is also enabled to wait for the JDBC client to submit the connection and query requests.