You can obtain JE by visiting the JE download page: http://www.oracle.com/technetwork/database/berkeleydb/downloads/index.html.
To install JE, simple untar or unzip the distribution to the
directory of your choice. If you use unzip, make sure to specify
the -U option in order to preserve case.
For more information on installing JE, see
JE_HOME/docs/relnotes.html,
where JE_HOME is the directory where you
unpacked JE.
JE is tested using, and certified against, Oracle JVM 1.6, Oracle JVM 1.7, and IBM JVM 1.6.
You can use JE with your application by adding
JE_HOME/lib/je-<version>.jar
to your application's classpath.
Beyond this manual, you can find documentation for JE at
JE_HOME/docs/index.html
directory. In particular, complete Javadoc for the JE API set
is available at
JE_HOME/docs/java/index.html.