Java™ Application Development on Linux - Dator

336Chapter 15Accessing the Data: An Introduction to JDBCposition it afterLast(), then getRow() to get the size, then position it backto beforeFirst() to be ready to read.15.6UPDATES, INSERTS, DELETESNot every action on a database returns a ResultSet. Operations that createthe tables in a database, or those that modify, insert, or delete rows of data don’treturn rows of values. For those sorts of SQL statements, we don’t callexecuteQuery()—we call executeUpdate() instead. It returns an int givingthe number of rows affected by the execution. In the case of a CREATE TABLEoperation, it simply returns 0.15.7REVIEWConnecting a Java application to a database is a key step in real applications.The mechanisms for doing that are varied and can be complicated. We’vepicked a single approach for connecting, to keep it simple and to highlight thesimilarities and differences between two different database implementations.The rest of the conversation with a database depends as much on yourSQL skills as on Java skills. Java will take strings of SQL, which can be parameterized,and, via JDBC calls, send them to be executed by the database. Theresults are like iterators; they can be retrieved, row after row, for further processing.Updates, inserts, and deletes are also easily done, with a few simple calls toprocess the SQL.15.8WHAT YOU STILL DON’T KNOWWe’ve skipped over lots of topics to keep this simple. There are a variety ofways to connect to a database that we haven’t covered; the most important onemay be the use of a DataSource instead of a DriverManager. As of Java 1.4.1,the DataSource is the preferred means of making connections to yourdatabase. While it makes the code more portable (e.g., if you’re planning onmoving around, changing databases and/or database servers), it is more complicatedto set up—there are more “moving parts” to get right. If you already havea Java Naming and Directory Interface (JNDI) service running, thought, it’svery straightforward (see page 254 and the following pages of Gallardo).