Merge pull request #275 from amedee/java

Fix Maven warnings

Java/pom.xml

@@ -12,7 +12,9 @@
     <properties>
         <java.version>1.8</java.version>
         <junit.jupiter.version>5.6.2</junit.jupiter.version>
+        <maven.maven-compiler-plugin.version>3.1</maven.maven-compiler-plugin.version>
         <maven.maven-surefire-plugin.version>3.0.0-M4</maven.maven-surefire-plugin.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
 
     <dependencies>
@@ -28,6 +30,7 @@
         <plugins>
             <plugin>
                 <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven.maven-compiler-plugin.version}</version>
                 <configuration>
                     <source>${java.version}</source>
                     <target>${java.version}</target>