Java Reference
In-Depth Information
}
}
Once the program has run, the database is populated and ready for use by the
UserDBJDBC
data accessor shown in
Using JDBC Prepared Statements
.
Finding JDBC Metadata
Problem
You want to learn about a database or table.
Solution
Read the documentation provided by your vendor or database administrator. Or ask the soft-
ware for a
MetaData
object.
Discussion
There are two classes relating to
metadata
(data about data) that you can ask for in the JDBC
API:
DatabaseMetaData
and
ResultSetMetaData
. Each of these has methods that let you
interrogate particular aspects. The former class is obtained from a get method in a
Connec-
tion
object; the latter from a get method in the given
ResultSet
.
ResultSetMetaData
First, let's look at the class
ResultsDecoratorHTML
, a “generic query” formatter shown in
ner
, simply defines a
Constructor
that saves the given
PrintWriter
as a field, as well as
providing two abstract methods that
ResultsDecoratorHTML
implements). When a program
using
ResultsDecoratorHTML
calls the
write()
method, the
ResultSet
is interrogated and
formatted into a neat little HTML table, using the column names from the
Res-
ultSetMetaData
as the headings for the HTML table. The nice part about this program is
that it responds to whatever columns are in the
ResultSet
, which need not be in the same
order as they are in the database. Consider the two queries:
