protected URL createSnapshot(final String foreignSource) throws MalformedURLException {
    System.err.println("--- creating snapshot for " + foreignSource + " ---");
    Requisition pending = m_pending.getRequisition(foreignSource);
    Requisition deployed = m_active.getRequisition(foreignSource);

    final Date deployedDate = deployed == null ? null : deployed.getDate();
    final Date pendingDate = pending == null ? null : pending.getDate();

    if (deployedDate == null)
      return RequisitionFileUtils.createSnapshot(m_pending, foreignSource, pending.getDate())
          .toURI()
          .toURL();
    if (pendingDate == null) return m_active.getRequisitionURL(foreignSource);

    final URL url;
    if (deployedDate.before(pendingDate)) {
      url =
          RequisitionFileUtils.createSnapshot(m_pending, foreignSource, pendingDate)
              .toURI()
              .toURL();
    } else {
      url = m_active.getRequisitionURL(foreignSource);
    }

    System.err.println("deployedDate = " + deployedDate);
    System.err.println("pendingDate  = " + pendingDate);
    System.err.println("url          = " + url);

    return url;
  }
  private void cleanUpSnapshots(final Requisition requisition) {
    final String foreignSource = requisition.getForeignSource();
    final Date pendingDate = m_pendingForeignSourceRepository.getRequisitionDate(foreignSource);

    final List<File> pendingSnapshots =
        RequisitionFileUtils.findSnapshots(m_pendingForeignSourceRepository, foreignSource);

    if (pendingDate != null) {
      /* determine whether to delete the pending requisition */
      boolean deletePendingRequisition = true;
      if (pendingSnapshots.size() > 0) {
        for (final File pendingSnapshotFile : pendingSnapshots) {
          if (isNewer(pendingSnapshotFile, pendingDate)) {
            // the pending file is newer than an in-process snapshot, don't delete it
            deletePendingRequisition = false;
            break;
          }
        }
      }
      if (deletePendingRequisition) {
        m_pendingForeignSourceRepository.delete(requisition);
      }
    }

    /* determine whether this requisition was imported from a snapshot, and if so, delete its snapshot file */
    RequisitionFileUtils.deleteResourceIfSnapshot(requisition);

    final Date deployedDate = m_deployedForeignSourceRepository.getRequisitionDate(foreignSource);
    if (deployedDate != null) {
      RequisitionFileUtils.deleteSnapshotsOlderThan(
          getPendingForeignSourceRepository(), foreignSource, deployedDate);
    }
  }
  @Test
  public void multipleSnapshotTest() throws URISyntaxException, InterruptedException {
    Requisition pendingReq = new Requisition("test");
    pendingReq.putNode(createNode("1"));
    m_pending.save(pendingReq);
    m_pending.flush();
    final String foreignSource = pendingReq.getForeignSource();
    pendingReq = m_pending.getRequisition(foreignSource);
    final File pendingSnapshotA =
        RequisitionFileUtils.createSnapshot(m_pending, foreignSource, pendingReq.getDate());

    // Now, start a new pending update after the original snapshot is "in progress"
    pendingReq.updateDateStamp();
    m_pending.save(pendingReq);
    m_pending.flush();

    final File pendingSnapshotB =
        RequisitionFileUtils.createSnapshot(m_pending, foreignSource, pendingReq.getDate());

    // "import" the A snapshot
    m_repository.importResourceRequisition(new FileSystemResource(pendingSnapshotA));

    assertFalse(pendingSnapshotA.exists());
    assertTrue(pendingSnapshotB.exists());

    // since there's still a newer snapshot in-progress, it is safe to delete the pending test.xml
    URL pendingUrl = m_pending.getRequisitionURL(foreignSource);
    assertNotNull(pendingUrl);
    assertFalse(new File(pendingUrl.toURI()).exists());

    // then, "import" the B snapshot
    final Requisition bReq =
        m_repository.importResourceRequisition(new FileSystemResource(pendingSnapshotB));

    assertFalse(pendingSnapshotA.exists());
    assertFalse(pendingSnapshotB.exists());

    // now the pending test.xml should be gone
    pendingUrl = m_pending.getRequisitionURL(foreignSource);
    assertNotNull(pendingUrl);
    assertFalse(new File(pendingUrl.toURI()).exists());

    // the last (B) pending import should match the deployed
    final Requisition deployedRequisition = m_active.getRequisition(foreignSource);
    assertEquals(deployedRequisition.getDate().getTime(), bReq.getDate().getTime());
  }
  @Test
  public void simpleSnapshotTest() throws URISyntaxException {
    Requisition pendingReq = new Requisition("test");
    pendingReq.putNode(createNode("1"));
    m_pending.save(pendingReq);
    m_pending.flush();
    pendingReq = m_pending.getRequisition(pendingReq.getForeignSource());
    final File pendingSnapshot =
        RequisitionFileUtils.createSnapshot(
            m_pending, pendingReq.getForeignSource(), pendingReq.getDate());

    m_repository.importResourceRequisition(new FileSystemResource(pendingSnapshot));

    assertFalse(pendingSnapshot.exists());
    final URL pendingUrl = m_pending.getRequisitionURL(pendingReq.getForeignSource());
    final File pendingFile = new File(pendingUrl.toURI());
    assertFalse(pendingFile.exists());
  }
  @Test
  public void testSpc674RaceCondition() throws Exception {
    final String foreignSource = "spc674";

    System.err.println(
        "=== create a requisition like the ReST service does, import it immediately ===");
    final Requisition initial = new Requisition(foreignSource);
    initial.putNode(createNode("1"));
    initial.updateDateStamp();
    m_pending.save(initial);

    final URL node1Snapshot = createSnapshot(foreignSource);
    Resource resource = new UrlResource(node1Snapshot);
    doImport(resource);

    Thread.sleep(5);
    List<String> files = getImports(foreignSource);
    assertEquals(1, files.size());

    System.err.println("=== create another snapshot, but don't import it yet ===");
    initial.putNode(createNode("2"));
    initial.updateDateStamp();
    m_pending.save(initial);
    final URL node2Snapshot = createSnapshot(foreignSource);

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(3, files.size());

    System.err.println("=== create yet another snapshot, and don't import it yet ===");
    initial.putNode(createNode("3"));
    initial.updateDateStamp();
    m_pending.save(initial);
    final URL node3Snapshot = createSnapshot(foreignSource);

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(4, files.size());

    System.err.println("=== import of the second file finishes ===");
    doImport(new UrlResource(node2Snapshot));

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(2, files.size());

    System.err.println("=== fourth node is sent to the ReST interface ===");
    final Requisition currentPending =
        RequisitionFileUtils.getLatestPendingOrSnapshotRequisition(m_pending, foreignSource);
    assertNotNull(currentPending);
    assertEquals(initial.getDate(), currentPending.getDate());
    currentPending.putNode(createNode("4"));
    currentPending.updateDateStamp();
    m_pending.save(currentPending);
    final URL node4Snapshot = createSnapshot(foreignSource);

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(4, files.size());

    System.err.println("=== import of the third file finishes ===");
    doImport(new UrlResource(node3Snapshot));

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(2, files.size());

    System.err.println("=== import of the fourth file finishes ===");
    doImport(new UrlResource(node4Snapshot));

    Thread.sleep(5);
    files = getImports(foreignSource);
    assertEquals(1, files.size());
  }
 private boolean isNewer(final File snap, final Date date) {
   return RequisitionFileUtils.isNewer(snap, date);
 }