Java Enterprise in a Nutshell, Second Edition

Metadata

Most JDBC programs are designed to work with a specific database and particular tables in that database; the program knows exactly what kind of data it is dealing with. Some applications, however, need to dynamically discover information about result set structures or underlying database configurations. This information is called metadata, and JDBC provides two classes for dealing with it: DatabaseMetaData and ResultSetMetaData. If you are developing a JDBC application that will be deployed outside a known environment, you need to be familiar with these interfaces.

DatabaseMetaData

You can retrieve general information about the structure of a database with the java.sql.DatabaseMetaData interface. By making thorough use of this class, a program can tailor its SQL and use of JDBC on the fly, to accommodate different levels of database and JDBC driver support.

Database metadata is associated with a particular connection, so DatabaseMetaData objects are created with the getMetaData( ) method of Connection:

DatabaseMetaData dbmeta = con.getMetaData(  );

DatabaseMetaData provides an overwhelming number of methods you can call to get actual configuration information about the database. Some of these return String objects (getURL( )), some return boolean values (nullsAreSortedHigh( )), and still others return integers (getMaxConnections( )).

A number of other methods return ResultSet objects. These methods, such as getColumns( ), getTableTypes( ), and getPrivileges( ) ...