SHS-NG M2: Store FsHistoryProvider listing data in LevelDB.

common/kvstore/src/main/java/org/apache/spark/kvstore/GenericArrayKey.java

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+/*
+ * 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.spark.kvstore;
+
+import java.lang.reflect.Array;
+
+import com.google.common.base.Objects;
+
+/**
+ * A class that wraps a generic array so that it can be used as a key in a map, sorted or not.
+ *
+ * The implementation of {@link #compareTo(GenericArrayKey)} makes two assumptions:
+ * - All elements are instances of Comparable
+ * - When comparing two arrays, they both contain elements of the same type in corresponding
+ *   indices.
+ *
+ * Otherwise, ClassCastExceptions may occur. The equality method can compare any two arrays.
+ *
+ * This class is not efficient and is mostly meant to compare really small arrays, like those
+ * generally used as indices and keys in a KVStore.
+ */
+public class GenericArrayKey implements Comparable<GenericArrayKey> {
+
+  private final Object key;
+
+  public GenericArrayKey(Object key) {
+    this.key = key;
+  }
+
+  @Override
+  public boolean equals(Object other) {
+    if (!(other instanceof GenericArrayKey)) {
+      return false;
+    }
+
+    Object comp = ((GenericArrayKey) other).key;
+    int l1 = Array.getLength(key);
+    int l2 = Array.getLength(comp);
+
+    if (l1 != l2) {
+      return false;
+    }
+
+    for (int i = 0; i < l1; i++) {
+      if (!Objects.equal(Array.get(key, i), Array.get(comp, i))) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+
+  @Override
+  public int hashCode() {
+    int code = 0;
+    int length = Array.getLength(key);
+    for (int i = 0; i < length; i++) {
+      code += Array.get(key, i).hashCode();
+    }
+    return 31 * code;
+  }
+
+  @Override
+  @SuppressWarnings("unchecked")
+  public int compareTo(GenericArrayKey other) {
+    int len = Math.min(Array.getLength(key), Array.getLength(other.key));
+    for (int i = 0; i < len; i++) {
+      int diff = ((Comparable<Object>) Array.get(key, i)).compareTo(
+          (Comparable<Object>) Array.get(other.key, i));
+      if (diff != 0) {
+        return diff;
+      }
+    }
+
+    return Array.getLength(key) - Array.getLength(other.key);
+  }
+
+}