Java™ Application Development on Linux - Dator

334Chapter 15Accessing the Data: An Introduction to JDBCIf this all seems rather simplistic, well, it is. It may not be a very sophisticatedway of blending SQL with Java, but it is very effective. Notice that youdon’t get any syntax checking on the SQL query when you write your program,though it will throw an exception at runtime if you try to execute ungrammaticalSQL. For this reason it is not uncommon to try out all your SQL beforehand,cutting and pasting the queries out of the SQL program that you use fordirectly talking with your database. Some developers even like to keep theirqueries in files, to be read at runtime. This has the added flexibility (and risk)of being able to change the query without recompiling the code. Since the recompiledoesn’t provide any syntax checking on your query string anyway, itseems a reasonable way to go, provided that you properly write-protect the filescontaining the queries.15.5GETTING RESULTSReturning to our example, we see that we can execute the query on theStatement object and then get out the results:ResultSet rs = stmt.executeQuery();// read the resultswhile(rs.next()) {int id = rs.getInt("id");String pw = rs.getString("pw");}System.out.println("id="+id);The results of a query are returned in a ResultSet object. The easiest wayto think of it is to consider it an iterator over the rows that result from thequery. In its simple form it is, like an iterator, a one-pass, once-through traversalof the data. Since the result set is iterating over rows, we need to get at the individualcolumns of results with a further method call on the ResultSet. Youcan see that inside the while loop of the example.The query was built to retrieve the columns id and pw from our table.The getInt() and getString() methods use those column names to retrievethe data from the ResultSet.