GH-1322: Add Checkstyle rule to ensure Java files get right header

eclipse/checkstyle.xml

@@ -15,6 +15,12 @@
         <module name="UnusedLocalVariable"/>
     </module>
 
+    <module name="RegexpHeader">
+        <property name="headerFile" value="./eclipse/java.header"/>
+        <property name="multiLines" value="2, 3, 14"/>
+        <property name="fileExtensions" value="java"/>
+    </module>
+
     <module name="RegexpSingleline">
         <property name="format" value="\s+$"/>
         <property name="message" value="No trailing white space allowed."/>

eclipse/java.header

@@ -0,0 +1,15 @@
+^/\*+$
+^ \* Copyright \(c\) \d\d\d\d(-\d\d\d\d)? .+\.$
+^ \*$
+^ \* All rights reserved\. This program and the accompanying materials$
+^ \* are made available under the terms of the Eclipse Public License v2\.0$
+^ \* and Eclipse Distribution License v1\.0 which accompany this distribution\.$
+^ \*$
+^ \* The Eclipse Public License is available at$
+^ \*    http://www\.eclipse\.org/legal/epl-v20\.html$
+^ \* and the Eclipse Distribution License is available at$
+^ \*    http://www\.eclipse\.org/org/documents/edl-v10\.html\.$
+^ \*$
+^ \* Contributors:$
+^ \*    .+$
+^ \*+/$

leshan-core/pom.xml

@@ -60,6 +60,12 @@ Contributors:
 
   <build>
     <plugins>
+      <plugin>
+        <artifactId>maven-checkstyle-plugin</artifactId>
+        <configuration>
+          <excludes>org/eclipse/leshan/core/util/Base64.java,org/eclipse/leshan/core/util/BaseNCodec.java,org/eclipse/leshan/core/util/Hex.java,org/eclipse/leshan/core/util/RandomStringUtils.java,org/eclipse/leshan/core/util/StringUtils.java,org/eclipse/leshan/core/util/Validate.java,org/eclipse/leshan/core/util/datatype/ULong.java</excludes>
+        </configuration>
+      </plugin>
       <plugin>
         <!-- Create test-jar to reuse it in integration-tests -->
         <artifactId>maven-jar-plugin</artifactId>