6.3.3.4.2 Fetching by Column:
When a valid data row has been retrieved, we need to get each column from that row. To do that, a different getXXX() method should be used based on the different data type of the returned data. One can use either the name of the column or the index of that column to get the data value. For example, in our LogIn Table, both the user _ name and the pass _ word are Strings; therefore, a getString() method should be used with the index of each column. A point to be noted is that the first column has an index of 1, not 0. If the name of each column, not an index, is used for the getString() method, the code can be written as
while (rs.next()){
username = rs.getString(“user _ name”); password = rs.getString(“pass _ word”); }
One of the most important methods in the ResultSet class is getObject(). The advantage of using this method is that a returned datum, which is stored in a ResultSet object with its data type unknown (a datum is dynamically created), can be automatically converted from its Oracle data type to the ideal Java data type. This method outperforms any other getXXX() method, since the data type of returned data must be known before a suiTable getXXX() method can be used to fetch the returned data.
The findColumn() method is used to find the index of a column if the name of that column is given, and the close() method is used to close a ResultSet instance.
The getMetaData() method is a very good and convenient method, and it allows users to have a detailed and clear picture of the structure and properties of data returned to a ResultSet. A ResultSetMetaData object, which contains all pieces of necessary information about the returned data stored in a ResultSet instance, is returned when this method is executed. By using dif-ferent methods of the ResultSetMetaData class, we can obtain a clear view of the returned data. For example, by using the getColumnCount() method, we can find how many columns in all have been retrieved and stored in the ResultSet. By using getTableName(), getColumnName() and getColumnType(), we can find the name of the data Table we queried, the name of column we just fetched and the data type of that column. A more detailed discussion of the ResultSetMetaData component will be given in later sections.
Now that we have some basic and necessary understanding of the Java JDBC driver, statement class, execution methods and ResultSet components, we are ready to develop our project to perform some data queries from our sample database.
Let’s start from the LogIn Table.