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<h2 class="title" style="clear: both"><a id="java_faq"></a>Java FAQ</h2>
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<div class="orderedlist">
<ol type="1">
<li>
<span class="bold">
<strong>On what platforms is the Berkeley DB
Java API supported?</strong>
</span>
<p>All platforms supported by Berkeley DB that have a
JVM compatible with J2SE 1.4 or above.</p>
</li>
<li>
<span class="bold">
<strong>How does the Berkeley DB Java API
relate to the J2EE standard?</strong>
</span>
<p>
The Berkeley DB Java API does not currently
implement any part of the J2EE standard. That said, it
does implement the implicit standard for Java <a class="ulink" href="http://download.oracle.com/javase/1.5.0/docs/guide/collections/" target="_top">
Java Collections</a>. The concept of a
transaction exists in several Java packages (J2EE, XA,
JINI to name a few). Support for these APIs will be
added based on demand in future versions of Berkeley
DB.
</p>
</li>
<li>
<span class="bold">
<strong>How should I incorporate db.jar and
the db native library into a Tomcat or other J2EE
application servers?</strong>
</span>
<p>
Tomcat and other J2EE application servers have the
ability to rebuild and reload code automatically. When
using Tomcat this is the case when "reloadable" is set
to "true". If your WAR file includes the db.jar it too
will be reloaded each time your code is reloaded. This
causes exceptions as the native library can't be
loaded more than once and there is no way to unload
native code. The solution is to place the db.jar in
$TOMCAT_HOME/common/lib and let Tomcat load that
library once at start time rather than putting it into
the WAR that gets reloaded over and over.
</p>
</li>
<li>
<span class="bold">
<strong>Can I use the Berkeley DB Java API
from within a EJB, a Servlet or a JSP page?</strong>
</span>
<p>
Yes. The Berkeley DB Java API can be used from
within all the popular J2EE application servers in
many different ways.
</p>
</li>
<li>
<span class="bold">
<strong>During one of the first calls to the
Berkeley DB Java API, a DbException is thrown with a
"Bad file number" or "Bad file descriptor"
message.</strong>
</span>
<p>
There are known large-file support bugs under JNI in
various releases of the JDK. Please upgrade to the
latest release of the JDK, and, if that does not solve
the problem, disable big file support using the
--disable-largefile configuration option.
</p>
</li>
<li>
<span class="bold">
<strong>How can I use native methods from a
debug build of the Java library?</strong>
</span>
<p>
Set Java's library path so that the debug version of
Berkeley DB's Java library appears, but the release
version does not. Berkeley DB tries to load the
release library first, and if that fails tries the
debug library.
</p>
</li>
<li>
<span class="bold">
<strong>Why is ClassNotFoundException thrown
when adding a record to the database, when a
SerialBinding is used?</strong>
</span>
<p>
This problem occurs if you copy the db.jar file into
the Java extensions (ext) directory. This will cause
the database code to run under the System class
loader, and it won't be able to find your application
classes.
</p>
<p>
You'll have to actually remove db.jar from the Java
extension directory. If you have more than one
installation of Java, be sure to remove it from all of
them. This is necessary even if db.jar is specified in
the classpath.
</p>
<p>
An example of the exception is:
</p>
<pre class="programlisting">collections.ship.basic.SupplierKey
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at com.sleepycat.bind.serial.StoredClassCatalog.
getClassInfo(StoredClassCatalog.java:211)
...</pre>
</li>
<li>
<span class="bold">
<strong>I'm upgrading my Java application to
Berkeley DB 4.3. Can I use the
com.sleepycat.db.internal package rather than porting
my code to the new API?</strong>
</span>
<p>
While it is possible to use the low-level API from
applications, there are some caveats that should be
considered when upgrading. The first is that the
internal API depends on some classes in the public API
such as DatabaseEntry.
</p>
<p>
In addition, the internal API is closer to the C API
and doesn't have some of the default settings that
were part of the earlier Java API. For example,
applications will need to set the DB_THREAD flag
explicitly if handles are to be used from multiple
threads, or subtle errors may occur.
</p>
</li>
</ol>
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