| 1 | package com.hammurapi.common.concurrent; |
| 2 | |
| 3 | import java.util.concurrent.Callable; |
| 4 | |
| 5 | /** |
| 6 | * Callable which callInternal() method is invoked only once. |
| 7 | * @author Pavel Vlasov |
| 8 | * |
| 9 | * @param <T> |
| 10 | */ |
| 11 | public abstract class OneOffCallable<T> implements Callable<T> { |
| 12 | |
| 13 | private boolean hasRun; |
| 14 | private Exception exception; |
| 15 | private T result; |
| 16 | |
| 17 | public synchronized T call() throws Exception { |
| 18 | if (!hasRun) { |
| 19 | try { |
| 20 | result = callInternal(); |
| 21 | } catch (Exception e) { |
| 22 | exception = e; |
| 23 | } finally { |
| 24 | hasRun = true; |
| 25 | } |
| 26 | } |
| 27 | |
| 28 | if (exception!=null) { |
| 29 | throw exception; |
| 30 | } |
| 31 | return result; |
| 32 | } |
| 33 | |
| 34 | /** |
| 35 | * This method is invoked once by the call() method. |
| 36 | * @return |
| 37 | */ |
| 38 | protected abstract T callInternal() throws Exception; |
| 39 | |
| 40 | } |