wro4j-core/src/main/java/ro/isdc/wro/model/resource/support/change/ResourceWatcher.java
private boolean isChanged(final Resource resource, final String groupName) {
    boolean changed = false;
    try {
      final String uri = resource.getUri();
      // using AtomicBoolean because we need to mutate this variable inside an anonymous class.
      final AtomicBoolean changeDetected = new AtomicBoolean(resourceChangeDetector.checkChangeForGroup(uri, groupName));
      if (!changeDetected.get() && resource.getType() == ResourceType.CSS) {
        final Reader reader = new InputStreamReader(locatorFactory.locate(uri));
        LOG.debug("\tCheck @import directive from {}", resource);
        createCssImportProcessor(changeDetected, groupName).process(resource, reader, new StringWriter());
      }
      changed = changeDetected.get();
    } catch (final IOException e) {
      LOG.debug("[FAIL] Cannot check {} resource (Exception message: {}). Assuming it is unchanged...", resource,
          e.getMessage());
    }
    LOG.debug("resource={}, changed={}", resource.getUri(), changed);
    return changed;
  }
private boolean isChanged(final Resource resource, final String groupName) {
    boolean changed = false;
    try {
      final String uri = resource.getUri();
      // using AtomicBoolean because we need to mutate this variable inside an anonymous class.
      final AtomicBoolean changeDetected = new AtomicBoolean(resourceChangeDetector.checkChangeForGroup(uri, groupName));
      if (!changeDetected.get() && resource.getType() == ResourceType.CSS) {
        final Reader reader = new InputStreamReader(locatorFactory.locate(uri));
        LOG.debug("\tCheck @import directive from {}", resource);
        createCssImportProcessor(changeDetected, groupName).process(resource, reader, new StringWriter());
      }
      changed = changeDetected.get();
    } catch (final IOException e) {
      LOG.debug("[FAIL] Cannot check {} resource (Exception message: {}). Assuming it is unchanged...", resource,
          e.getMessage());
    }
    LOG.debug("resource={}, changed={}", resource.getUri(), changed);
    return changed;
  }
Check if the resource was changed from previous run. The implementation uses resource content digest (hash) to
check for change.

@param resource
the {@link Resource} to check.
@return true if the resource was changed.