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<h2 class="title"><a id="java"></a>Chapter 5.
Java API
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<a href="java.html#java_conf">Java configuration</a>
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<p>Building the Berkeley DB java classes, the examples and the native support
library is integrated into the normal build process. See
<a class="xref" href="build_unix_conf.html" title="Configuring Berkeley DB">Configuring Berkeley DB</a> and
<a class="xref" href="build_win_java.html" title="Building the Java API">Building the Java API</a>
for more information.</p>
<p>We expect that you already installed the Java JDK or equivalent on your
system. For the sake of discussion, we assume that it is in a directory
called db-VERSION; for example, you downloaded a Berkeley DB archive, and you
did not change the top-level directory name. The files related to Java
are in three subdirectories of db-VERSION: java (the java source files),
libdb_java (the C++ files that provide the "glue" between java and
Berkeley DB) and examples_java (containing all examples code). The directory
tree looks like this:</p>
<pre class="programlisting">db-VERSION
|-- java
| `-- src
| `-- com
| `-- sleepycat
| |-- bind
| |-- db
| | `-- ...
| `-- util
|-- examples_java
| `-- src
| `-- db
| `-- ...
`-- libdb_java
`-- ...
</pre>
<p>This naming conforms to the de facto standard for naming java packages.
When the java code is built, it is placed into two jar files:
<code class="filename">db.jar</code>, containing the db package,
and <code class="filename">dbexamples.jar</code>, containing the examples.</p>
<p>For your application to use Berkeley DB successfully, you must set your
<code class="literal">CLASSPATH</code> environment variable to include the full pathname of
the db jar files as well as the classes in your java distribution.
On UNIX, <code class="literal">CLASSPATH</code> is a colon-separated
list of directories and jar files;
on Windows, it is separated by semicolons.
On UNIX, the jar files are put in your build directory, and when
you do the make install step, they are copied to the lib directory
of your installation tree. On Windows, the jar files are placed
in the Release or Debug subdirectory with your other objects.</p>
<p>The Berkeley DB Java classes are mostly implemented in native
methods. Before you can use them, you need to make sure that the
DLL or shared library containing the native methods can be found
by your Java runtime. On Windows, you should set your PATH variable
to include:</p>
<pre class="programlisting">
<code class="filename">db-VERSION\build_windows\Release</code>
</pre>
<p>On UNIX, you should set the
<code class="literal">LD_LIBRARY_PATH</code> environment variable or local equivalent
to include the Berkeley DB library installation directory. Of course, the
standard install directory may have been changed for your site; see your
system administrator for details.</p>
<p>On other platforms, the path can be set on the command line as follows
(assuming the shared library is in <code class="filename">/usr/local/BerkeleyDB/lib</code>:)</p>
<pre class="programlisting">% java -Djava.library.path=/usr/local/BerkeleyDB/lib ...</pre>
<p>Regardless, if you get the following exception when you run, you
probably do not have the library search path configured correctly:</p>
<pre class="programlisting">java.lang.UnsatisfiedLinkError</pre>
<p>Different Java interpreters provide different error messages if the
<code class="literal">CLASSPATH</code> value is incorrect, a typical error is the following:</p>
<pre class="programlisting">java.lang.NoClassDefFoundError</pre>
<p>To ensure that everything is running correctly, you may want to try a
simple test from the example programs in</p>
<pre class="programlisting">
<code class="filename">db-VERSION/examples_java/src/db</code>
</pre>
<p>For example, the following sample program will prompt for text input
lines, which are then stored in a Btree database named <code class="filename">access.db</code> in
your current directory:</p>
<pre class="programlisting">% java db.AccessExample</pre>
<p>Try giving it a few lines of input text and then end-of-file. Before
it exits, you should see a list of the lines you entered display with
data items. This is a simple check to make sure the fundamental
configuration is working correctly.</p>
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