Java Database Connectivity (JDBC) - An Introduction to Network Programming with Java - page 195

7.8 Meta Data

Meta data is 'data about data'. There are two categories of meta data available
through the JDBC API:

￿ data about the rows and columns returned by a query (i.e., data about ResultSet
objects);

￿ data about the database as a whole.

The fi rst of these is provided by interface ResultSetMetaData , an object of which
is returned by the ResultSet method getMetaData . Information available from a
ResultSetMetaData object includes the following:

￿ the number of fi elds/columns in a ResultSet object;

￿ the name of a specifi ed fi eld;

￿ the data type of a fi eld;

￿ the maximum width of a fi eld;

￿ the table to which a fi eld belongs.

Data about the database as a whole is provided by interface DatabaseMetaData ,
an object of which is returned by the Connection method getMetaData . However,
most Java developers will rarely fi nd a need for DatabaseMetaData and no further
mention will be made of it.
Before proceeding further, it is worth pointing out that the full range of SQL
types is represented in class java.sql.Types as a series of 28 named static integer
( int ) constants. The 8 that are likely to be of most use are listed below.

￿ DATE

￿ DECIMAL

￿ DOUBLE

￿ FLOAT

￿ INTEGER

￿ NUMERIC

￿ REAL

￿ VARCHAR

INTEGER and VARCHAR are particularly commonplace, the latter of these
corresponding to string values.
The example coming up makes use of the following ResultSetMetaData
methods, which return properties of the database fi elds held in a ResultSetMetaData
object.

￿ int getColumnCount()

￿ String getColumnName(<colNumber>)

￿ int getColumnType(<colNumber>)

￿ String getColumnTypeName(<colNumber>)