Database Programming with JDBC & Java, Second Edition

Meta-Data

Much of what you have done with JDBC so far requires you to know a lot about the database you are using, including the capabilities of the database engine and the data model against which you are operating. Requiring this level of knowledge may not bother you much, but JDBC does provide the tools to free you from these limitations. These tools come in the form of meta-data.

The term “meta” here means information about your data that does not interest the end users at all, but which you need to know in order to handle the data. JDBC provides two meta-data classes: java.sql.ResultSetMetaData and java.sql.DatabaseMetaData. The meta-data described by these classes was included in the original JDBC ResultSet and Connection classes. The team that developed the JDBC specification decided instead that it was better to keep the ResultSet and Connection classes small and simple to serve the most common database requirements. The extra functionality could be served by creating meta-data classes to provide the often esoteric information required by a minority of developers.

Result Set Meta-Data

As its name implies, the ResultSetMetaData class provides extra information about ResultSet objects returned from a database query. In the embedded queries you made earlier in the book, you hardcoded into your queries much of the information a ResultSetMetaData object gives you. This class provides you with answers to the following questions:

• How many columns are in the result set?

• Are column ...