LICENSE.txt

Except where otherwise indicated, the software in this project is
licensed under the GNU General Public License, version 2 (see the file
named COPYING), along with the Classpath Exception:

  Linking this library statically or dynamically with other modules is
  making a combined work based on this library.  Thus, the terms and
  conditions of the GNU General Public License cover the whole
  combination.

  As a special exception, the copyright holders of this library give you
  permission to link this library with independent modules to produce an
  executable, regardless of the license terms of these independent
  modules, and to copy and distribute the resulting executable under
  terms of your choice, provided that you also meet, for each linked
  independent module, the terms and conditions of the license of that
  module.  An independent module is a module which is not derived from
  or based on this library.  If you modify this library, you may extend
  this exception to your version of the library, but you are not
  obligated to do so.  If you do not wish to do so, delete this
  exception statement from your version.