checkstyle: add checks for license headers

config/checkstyle/checkstyle.xml

@@ -35,6 +35,19 @@
         <property name="max" value="80"/>
     </module>
 
+    <!-- Checks for headers                       -->
+    <!-- See https://checkstyle.org/checks/header -->
+    <module name="Header">
+        <property name="headerFile" value="${config_loc}/java-header"/>
+        <property name="ignoreLines" value="2"/>
+        <property name="fileExtensions" value="java"/>
+    </module>
+    <module name="SuppressionSingleFilter">
+        <property name="checks" value="Header"/>
+        <property name="files" value="com[/]jme3"/>
+        <property name="lines" value="1"/>
+    </module>
+
     <module name="TreeWalker">
         <module name="OuterTypeFilename"/>
         <module name="IllegalToken">

config/checkstyle/java-header

@@ -0,0 +1,25 @@
+/*
+ [Copyright information goes here.]
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are met:
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the distribution.
+ * Neither the name of the copyright holder nor the names of its contributors
+ may be used to endorse or promote products derived from this software without
+ specific prior written permission.
+
+ THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */