defaults for commit, abort and prepareForAbort

We see a lot of transaction implementations having to override commit
and rollback just to honor the API. Same happens for participants that
want to be engaged at abort time so they need to implement
AbortParticipant, but the prepareForAbort implementation just calls
prepare.

We now provide default implementations for those.

Author: ar

jpos/src/main/java/org/jpos/transaction/AbortParticipant.java

@@ -34,6 +34,7 @@ public interface AbortParticipant extends TransactionParticipant {
      * @param context transaction context
      * @return 0 [| NO_JOIN | READONLY)
      */
-    int  prepareForAbort(long id, Serializable context);
+    default int prepareForAbort(long id, Serializable context) {
+        return prepare (id, context);
+    }
 }
-

jpos/src/main/java/org/jpos/transaction/TransactionParticipant.java

@@ -42,7 +42,7 @@ public interface TransactionParticipant extends TransactionConstants {
      * @param id the Transaction identifier
      * @param context transaction context
      */
-    void commit(long id, Serializable context);
+    default void commit(long id, Serializable context) { }
 
     /**
      * Called by TransactionManager upon transaction commit.
@@ -52,6 +52,5 @@ public interface TransactionParticipant extends TransactionConstants {
      * @param id the Transaction identifier
      * @param context transaction context
      */
-    void abort(long id, Serializable context);
+    default void abort(long id, Serializable context) { }
 }
-