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The Codex »
Stop Using Class Dot Forname
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<h1 id="jdbc-drivers-and-classforname">JDBC Drivers and <code>Class.forName()</code></h1>
<p>The short version: stop using <code>Class.forName(driverClass)</code> to load JDBC
drivers. You don't need this, and haven't since Java 6. You arguably never
needed this.</p>
<p>This pattern appears all over the internet, and it's wrong.</p>
<h2 id="backstory">Backstory</h2>
<p>JDBC has more or less always provided two ways to set up <code>Connection</code> objects:</p>
<ol>
<li>
<p>Obtain them from a driver-provided <code>DataSource</code> class, which applications or
containers are expected to create for themselves.</p>
</li>
<li>
<p>Obtain them by passing a URL to <code>DriverManager</code>.</p>
</li>
</ol>
<p>Most people start with the latter, since it's very straightforward to use.
However, <code>DriverManager</code> needs to be able to locate <code>Driver</code> subclasses, and
the JVM doesn't permit class enumeration at runtime.</p>
<p>In the original JDBC release, <code>Driver</code> subclasses were expected to register
themselves on load, similar to</p>
<pre><code>public class ExampleDriver extends Driver {
static {
DriverManager.registerDriver(ExampleDriver.class);
}
}
</code></pre>
<p>Obviously, applications <em>can</em> force drivers to load using
<code>Class.forName(driverName)</code>, but this hasn't ever been the only way to do it.
<code>DriverManager</code> also provides <a href="https://docs.oracle.com/javase/8/docs/api/java/sql/DriverManager.html">a mechanism to load a set of named classes at
startup</a>,
via the <code>jdbc.drivers</code> <a href="http://docs.oracle.com/javase/tutorial/essential/environment/sysprop.html">system property</a>.</p>
<h2 id="jdbc-4-fixed-that">JDBC 4 Fixed That</h2>
<p>JDBC 4, which came out with Java 6 in the Year of our Lord <em>Two Thousand and
Six</em>, also loads drivers using the <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#Service%20Provider">service
provider</a>
system, which requires no intervention at all from deployers or application
developers.</p>
<p><em>You don't need to write any code to load a JDBC 4 driver.</em></p>
<h2 id="whats-the-harm">What's The Harm?</h2>
<p>It's harmless in the immediate sense: forcing a driver to load immediately
before JDBC would load it itself has no additional side effects. However, it's
a pretty clear indicator that you've copied someone else's code without
thoroughly understanding what it does, which is a bad habit.</p>
<h2 id="but-what-about-my-database">But What About My Database?</h2>
<p>You don't need to worry about it. All of the following drivers support JDBC
4-style automatic discovery:</p>
<ul>
<li>
<p>PostgreSQL (since version 8.0-321, in 2007)</p>
</li>
<li>
<p>Firebird (since <a href="http://tracker.firebirdsql.org/browse/JDBC-140">version 2.2, in 2009</a>)</p>
</li>
<li>
<p><a href="../mysql/choose-something-else">MySQL</a> (since <a href="http://dev.mysql.com/doc/relnotes/connector-j/en/news-5-0-0.html">version 5.0, in 2005</a>)</p>
</li>
<li>
<p>H2 (since day 1, as far as I can tell)</p>
</li>
<li>
<p>Derby/JavaDB (since <a href="https://issues.apache.org/jira/browse/DERBY-930">version 10.2.1.6, in 2006</a>)</p>
</li>
<li>
<p>SQL Server (version unknown, because MSDN is archaeologically hostile)</p>
</li>
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