[GitHub] [gobblin] homatthew commented on a diff in pull request #3648: [GOBBLIN-1779] Ability to filter datasets that contain non optional unions

["homatthew (via GitHub)" <gi...@apache.org>]

homatthew commented on code in PR #3648:
URL: https://github.com/apache/gobblin/pull/3648#discussion_r1130213358


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gobblin-data-management/src/main/java/org/apache/gobblin/data/management/dataset/DatasetsFinderFilteringDecorator.java:
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@@ -0,0 +1,104 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.gobblin.data.management.dataset;
+
+import com.google.common.annotations.VisibleForTesting;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Properties;
+import java.util.stream.Collectors;
+import org.apache.gobblin.dataset.Dataset;
+import org.apache.gobblin.dataset.DatasetsFinder;
+import org.apache.gobblin.util.PropertiesUtils;
+import org.apache.gobblin.util.function.CheckedExceptionPredicate;
+import org.apache.gobblin.util.reflection.GobblinConstructorUtils;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.Path;
+
+
+/**
+ * A decorator for filtering datasets after a {@link DatasetsFinder} finds a {@link List} of {@link Dataset}s
+ */
+public class DatasetsFinderFilteringDecorator<T extends Dataset> implements DatasetsFinder<T> {
+  private static final String PREFIX = "filtering.datasets.finder.";
+  public static final String DATASET_CLASS = PREFIX + "class";
+  public static final String ALLOWED = PREFIX + "allowed.predicates";
+  public static final String DENIED = PREFIX + "denied.predicates";
+
+  protected DatasetsFinder<T> datasetFinder;
+  protected List<CheckedExceptionPredicate<T,IOException>> allowDatasetPredicates;
+  protected List<CheckedExceptionPredicate<T,IOException>> denyDatasetPredicates;
+
+  public DatasetsFinderFilteringDecorator(FileSystem fs, Properties properties) throws IOException {
+    this.datasetFinder = DatasetUtils.instantiateDatasetFinder(
+        DATASET_CLASS, properties, fs, DefaultFileSystemGlobFinder.class.getName());
+    this.allowDatasetPredicates = instantiatePredicates(ALLOWED, properties);
+    this.denyDatasetPredicates = instantiatePredicates(DENIED, properties);
+  }
+
+  @VisibleForTesting
+  DatasetsFinderFilteringDecorator(
+      DatasetsFinder<T> datasetsFinder,
+      List<CheckedExceptionPredicate<T,IOException>> allowDatasetPredicates,
+      List<CheckedExceptionPredicate<T,IOException>> denyDatasetPredicates) {
+    this.datasetFinder = datasetsFinder;
+    this.allowDatasetPredicates = allowDatasetPredicates;
+    this.denyDatasetPredicates = denyDatasetPredicates;
+  }
+
+  @Override
+  public List<T> findDatasets() throws IOException {
+    List<T> datasets = datasetFinder.findDatasets();
+    List<T> allowedDatasets = null;

Review Comment:
   In hindsight, does this value really matter? We can just return allowedDatasets as-is. 
   
   But to answer your question. We can never return null from this method. We always throw an exception or allowedDatasets is overwritten by datasets (which cannot be null)



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