[OPENJPA-2984] Record why an id class is no longer checked for Serializable

openjpa-persistence/src/main/java/org/apache/openjpa/persistence/AnnotationPersistenceMetaDataParser.java

@@ -637,6 +637,13 @@ private ClassMetaData parseClassAnnotations() {
                     break;
                 case ID_CLASS:
                     if (isMetaDataMode()) {
+                        // Jakarta Persistence 3.2 (section 2.4.1) no longer requires
+                        // the primary key class to be public or to implement
+                        // Serializable, so neither is validated here; see
+                        // OPENJPA-2940 and OPENJPA-2984. A non-serializable id
+                        // class does still prevent serializing the identity
+                        // object it is wrapped in, which detached entities,
+                        // remote commit events and a distributed data cache do.
                         meta.setObjectIdType(((IdClass) anno).value(), true);
                     }
                     break;

openjpa-persistence/src/main/java/org/apache/openjpa/persistence/XMLPersistenceMetaDataParser.java

@@ -81,7 +81,6 @@
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
-import java.io.Serializable;
 import java.lang.reflect.Field;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
@@ -1347,6 +1346,12 @@ protected boolean startIdClass(Attributes attrs)
         } catch (Throwable t) {
             throw getException(_loc.get("invalid-id-class", meta, cls), t);
         }
+        // Jakarta Persistence 3.2 (section 2.4.1) no longer requires the primary
+        // key class to be public or to implement Serializable, so neither is
+        // validated here; see OPENJPA-2940 and OPENJPA-2984. A non-serializable
+        // id class does still prevent serializing the identity object it is
+        // wrapped in, which detached entities, remote commit events and a
+        // distributed data cache do.
         meta.setObjectIdType(idCls, true);
         return true;
     }

openjpa-project/src/doc/manual/jpa_overview_pc.xml

@@ -838,17 +838,7 @@ following criteria:
             <itemizedlist>
                 <listitem>
                     <para>
-The class must be public.
-                    </para>
-                </listitem>
-                <listitem>
-                    <para>
-The class must be serializable.
-                    </para>
-                </listitem>
-                <listitem>
-                    <para>
-The class must have a public no-args constructor.
+The class must have a no-args constructor.
                     </para>
                 </listitem>
                 <listitem>
@@ -881,6 +871,19 @@ hierarchy mirrors the inheritance hierarchy of the owning entity classes (see
             </itemizedlist>
             <note>
                 <para>
+Jakarta Persistence 3.2 no longer requires the identity class to be public or to
+implement <classname>java.io.Serializable</classname>, and OpenJPA no longer
+enforces either. An identity class that does not implement
+<classname>Serializable</classname> can, however, not be used where OpenJPA has
+to serialize the identity object it is wrapped in: serializing a detached
+entity, remote commit events in a clustered configuration, and a distributed
+data cache. Those fail with a
+<classname>java.io.NotSerializableException</classname> naming the identity
+class.
+                </para>
+            </note>
+            <note>
+                <para>
 Though you may still create identity classes by hand, OpenJPA provides the
 <classname>appidtool</classname> to automatically generate proper identity
 classes based on your identity fields. See