CloseSql.qhelp

<!DOCTYPE qhelp PUBLIC
  "-//Semmle//qhelp//EN"
  "qhelp.dtd">
<qhelp>


<overview>
<p>A database resource in the <code>java.sql</code> package that is opened
but not closed may cause a resource leak and ultimately resource exhaustion.
</p>

</overview>
<recommendation>

<p>Ensure that the resource is always closed to avoid a resource leak. Note that, because of exceptions,
it is safest to close a resource in a <code>finally</code> block.
</p>

<p>For Java 7 or later, the recommended way to close resources that implement <code>java.lang.AutoCloseable</code>
is to declare them within a <code>try-with-resources</code> statement, so that they are closed implicitly.</p>

</recommendation>
<example>

<p>In the following example, the resources <code>stmt</code> and <code>rs</code> are opened but not closed.</p>

<sample src="CloseSql.java" />

<p>In the following example, the resources <code>stmt</code> and <code>rs</code> are
declared within a <code>try-with-resources</code> block and are thus closed implicitly.</p>

<sample src="CloseSqlGood.java" />

<p>Note that the <code>Connection</code> that is passed into the method is a long-lived object
that was created elsewhere and therefore need not be closed locally. It should instead be closed
by the code that created it or by a server shutdown procedure, as appropriate.</p>

</example>
<references>


<li>
  IBM developerWorks: <a href="https://web.archive.org/web/20201109041839/http://www.ibm.com/developerworks/java/library/j-jtp03216/index.html">Java theory and practice: Good housekeeping practices</a>.
</li>
<li>
  The Java Tutorials: <a href="https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html">The try-with-resources Statement</a>.
</li>


</references>
</qhelp>