The following JDBC interfaces are subinterfaces of the Wrapper interface:

• java.sql.Connection
• java.sql.DatabaseMetaData
• java.sql.ParameterMetaData
• java.sql.ResultSet
• java.sql.ResultSetMetaData
• java.sql.Statement
• javax.sql.Datasource

The Wrapper interface consists of two methods:

• isWrapperFor - Returns true if this either implements the interface argument or is directly or indirectly a wrapper for an object that does.
• unwrap - Returns an object that implements the given interface to allow access to non-standard methods, or standard methods not exposed by the proxy.

  Statement stmt = conn.createStatement();
  Class clzz = Class.forName("oracle.jdbc.OracleStatement");
  OracleStatement os;
  if(stmt.isWrapperFor(clzz)) {
     os = stmt.unwrap(clzz);
     os.defineColumnType(1, Types.NUMBER);
  }