pom: Check API changes against SemVer rules during build

Use japicmp to detect any changes in the public API compared to the
previous release, and fail the build if the rules of semantic versioning
are violated.

This is run during the "verify" phase, just before the "install" phase.
It also outputs the API differences in the target/japicmp folder.

pom.xml

@@ -77,6 +77,7 @@
     <version.gpg.plugin>1.5</version.gpg.plugin>
     <version.install.plugin>2.5.2</version.install.plugin>
     <version.jacoco.plugin>0.8.10</version.jacoco.plugin>
+    <version.japicmp.plugin>0.20.0</version.japicmp.plugin>
     <version.javadoc.plugin>3.4.0</version.javadoc.plugin>
     <version.source.plugin>3.2.1</version.source.plugin>
     <version.jar.plugin>3.3.0</version.jar.plugin>
@@ -393,6 +394,11 @@
           <artifactId>jacoco-maven-plugin</artifactId>
           <version>${version.jacoco.plugin}</version>
         </plugin>
+        <plugin>
+          <groupId>com.github.siom79.japicmp</groupId>
+          <artifactId>japicmp-maven-plugin</artifactId>
+          <version>${version.japicmp.plugin}</version>
+        </plugin>
         <plugin>
           <groupId>org.sonatype.plugins</groupId>
           <artifactId>nexus-staging-maven-plugin</artifactId>
@@ -457,6 +463,28 @@
           </execution>
         </executions>
       </plugin>
+
+      <plugin>
+        <groupId>com.github.siom79.japicmp</groupId>
+        <artifactId>japicmp-maven-plugin</artifactId>
+        <configuration>
+          <!-- Old and new versions are not specified, so we compare the latest released version with the build artefact -->
+          <parameter>
+            <!-- Break the build in case the semantic versioning is violated -->
+            <breakBuildBasedOnSemanticVersioning>true</breakBuildBasedOnSemanticVersioning>
+            <!-- Output only modified classes/methods in the report -->
+            <onlyModified>true</onlyModified>
+          </parameter>
+        </configuration>
+        <executions>
+          <execution>
+            <phase>verify</phase>
+            <goals>
+              <goal>cmp</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>