Fix race condition in static class initialization

Author: atextor

core/esmf-aspect-meta-model-interface/src/main/java/org/eclipse/esmf/metamodel/vocabulary/RdfNamespace.java

@@ -57,9 +57,9 @@ static Map<String, String> createPrefixMap( final KnownVersion metaModelVersion
       result.put( samme.getShortForm(), samme.getNamespace() );
       final UNIT unit = new UNIT( metaModelVersion, samm );
       result.put( unit.getShortForm(), unit.getNamespace() );
-      result.put( SammNs.RDF.getShortForm(), SammNs.RDF.getNamespace() );
-      result.put( SammNs.RDFS.getShortForm(), SammNs.RDFS.getNamespace() );
-      result.put( SammNs.XSD.getShortForm(), SammNs.XSD.getNamespace() );
+      result.put( SammNs.RDF().getShortForm(), SammNs.RDF().getNamespace() );
+      result.put( SammNs.RDFS().getShortForm(), SammNs.RDFS().getNamespace() );
+      result.put( SammNs.XSD().getShortForm(), SammNs.XSD().getNamespace() );
       return result;
    }
 
@@ -69,9 +69,9 @@ static Map<String, String> createPrefixMap() {
       result.put( SammNs.SAMMC.getShortForm(), SammNs.SAMMC.getNamespace() );
       result.put( SammNs.SAMME.getShortForm(), SammNs.SAMME.getNamespace() );
       result.put( SammNs.UNIT.getShortForm(), SammNs.UNIT.getNamespace() );
-      result.put( SammNs.RDF.getShortForm(), SammNs.RDF.getNamespace() );
-      result.put( SammNs.RDFS.getShortForm(), SammNs.RDFS.getNamespace() );
-      result.put( SammNs.XSD.getShortForm(), SammNs.XSD.getNamespace() );
+      result.put( SammNs.RDF().getShortForm(), SammNs.RDF().getNamespace() );
+      result.put( SammNs.RDFS().getShortForm(), SammNs.RDFS().getNamespace() );
+      result.put( SammNs.XSD().getShortForm(), SammNs.XSD().getNamespace() );
       return result;
    }
 }

core/esmf-aspect-meta-model-interface/src/main/java/org/eclipse/esmf/metamodel/vocabulary/SammNs.java

@@ -20,14 +20,16 @@
 /**
  * RDF vocabularies of the SAMM meta model namespaces
  */
+@SuppressWarnings( { "checkstyle:AbbreviationAsWordInName", "checkstyle:MethodName" } ) // RDF vocabularies are exempt from naming rules
 public class SammNs {
    public static final SAMM SAMM = new SAMM( KnownVersion.getLatest() );
    public static final SAMMC SAMMC = new SAMMC( KnownVersion.getLatest() );
    public static final SAMME SAMME = new SAMME( KnownVersion.getLatest(), SAMM );
    public static final UNIT UNIT = new UNIT( KnownVersion.getLatest(), SAMM );
-   public static final RdfNamespace RDF = new SimpleRdfNamespace( "rdf", org.apache.jena.vocabulary.RDF.getURI() );
-   public static final RdfNamespace RDFS = new SimpleRdfNamespace( "rdfs", org.apache.jena.vocabulary.RDFS.getURI() );
-   public static final RdfNamespace XSD = new SimpleRdfNamespace( "xsd", org.apache.jena.vocabulary.XSD.getURI() );
+
+   private static RdfNamespace RDF;
+   private static RdfNamespace RDFS;
+   private static RdfNamespace XSD;
 
    private SammNs() {
    }
@@ -41,12 +43,33 @@ public static Stream<RdfNamespace> sammNamespaces() {
       return Stream.of( SAMM, SAMMC, SAMME, UNIT );
    }
 
+   public static synchronized RdfNamespace RDF() {
+      if ( RDF == null ) {
+         RDF = new SimpleRdfNamespace( "rdf", org.apache.jena.vocabulary.RDF.getURI() );
+      }
+      return RDF;
+   }
+
+   public static synchronized RdfNamespace RDFS() {
+      if ( RDFS == null ) {
+         RDFS = new SimpleRdfNamespace( "rdfs", org.apache.jena.vocabulary.RDFS.getURI() );
+      }
+      return RDFS;
+   }
+
+   public static synchronized RdfNamespace XSD() {
+      if ( XSD == null ) {
+         XSD = new SimpleRdfNamespace( "xsd", org.apache.jena.vocabulary.XSD.getURI() );
+      }
+      return XSD;
+   }
+
    /**
     * All "well-known" RDF namespaces
     *
     * @return the namespaces
     */
    public static Stream<RdfNamespace> wellKnownNamespaces() {
-      return Stream.concat( sammNamespaces(), Stream.of( RDF, RDFS, XSD ) );
+      return Stream.concat( sammNamespaces(), Stream.of( RDF(), RDFS(), XSD() ) );
    }
 }