6.3.3.4 Use ResultSet Object
The ResultSet class contains 25 methods, and the most popular methods used are:
- getXXX()
- getMetaData()
- next()
- findColumn()
- close()
The ResultSet object can be created by either executing the executeQuery() or getRe-sultSet() method, which means that the ResultSet instance cannot be created or used without executing a query operation first. Similarly to a Statement object, a Connection object must be first created, and then the Statement component can be created and implemented based on the Connection object to perform a query.
The queried result or data is stored in the ResultSet with a certain format, generally in a 2D tabular form with columns and rows. Each column can be mapped onto an array, and each row can be considered a Vector. Therefore, the easiest way to map a ResultSet is to create an array of Vectors.
When a query operation is performed and a ResultSet instance is created, next we need to retrieve the queried result from the ResultSet object by using a suiTable getXXX() method. Depending on the returned data type of the queried result, different methods should be used, such as getInt(), getString(), getByte(), getDouble(), getShort() and getObject().
Two different methods can be used to get returned data from a ResultSet instance: fetching by row and fetching by column.
6.3.3.4.1 Fetching by Row:
Since the returned data can be stored in a ResultSet in tabular form, the data can be picked up row by row. The next() method in the ResultSet class is specially used for this purpose. Each row can be selected by using a cursor that can be considered a pointer to point to each row. The next() method can move the row pointer from the current position to the next row. When a login query is executed, a ResultSet instance, rs, can be created and returned. Initially the cursor points to a row that is just above the first row, and you have to run the next() method once to make it point to the first data row; then you can repeat running this method by using a while() loop to scan the whole Table until the last row. A true is returned by the next() method if a valid row has been found and pointed to, and a false is returned if the cursor points to a null row, which means that no more valid rows can be found and the bottom of the ResultSet has been reached.