ThreadLocal

The ThreadLocal class behaves much like the various Reference classes in java.lang.ref; it acts as an indirect handle for storing or retrieving a value. Listing 1 shows the ThreadLocal interface.

public class ThreadLocal { 
  public Object get();
  public void set(Object newValue);
  public Object initialValue();
}

See: Exploiting ThreadLocal to enhance scalability

public class EntityChangeTracker {

 private static ThreadLocal<List<EntityChange>> entityChangeThreadLocal = new ThreadLocal<List<EntityChange>>() {
  protected List<EntityChange> initialValue() {
   return new ArrayList<EntityChange>();
  }
 };
 
 public static List<EntityChange> getEntityChanges() {
  return entityChangeThreadLocal.get();
 }
 
 public static void addEntityChange(Entity<?> e, AuditOperation opr) {
  List<EntityChange> list = entityChangeThreadLocal.get();
  list.add(new EntityChange(e, opr));
 }
  
 public static void clear() {
  entityChangeThreadLocal.get().clear();
 }
}