[GitHub] [accumulo] ctubbsii commented on a change in pull request #1257: Created SequenceLexicoder to resolve #1252 (2.0)

[GitBox <gi...@apache.org>]

ctubbsii commented on a change in pull request #1257: Created SequenceLexicoder to resolve #1252 (2.0)
URL: https://github.com/apache/accumulo/pull/1257#discussion_r304202195
 
 

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 File path: core/src/main/java/org/apache/accumulo/core/client/lexicoder/SequenceLexicoder.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.accumulo.core.client.lexicoder;
+
+import static java.util.Objects.requireNonNull;
+import static org.apache.accumulo.core.clientImpl.lexicoder.ByteUtils.concat;
+import static org.apache.accumulo.core.clientImpl.lexicoder.ByteUtils.escape;
+import static org.apache.accumulo.core.clientImpl.lexicoder.ByteUtils.split;
+import static org.apache.accumulo.core.clientImpl.lexicoder.ByteUtils.unescape;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.accumulo.core.clientImpl.lexicoder.AbstractLexicoder;
+
+/**
+ * A Lexicoder to encode/decode a Java List to/from a byte array where the concatenation of each
+ * encoded element sorts lexicographically.
+ *
+ * Note: Unlike {@link ListLexicoder}, this implementation supports empty lists.
+ *
+ * The lists are encoded with the elements separated by null (0x0) bytes, which null bytes appearing
+ * in the elements escaped as two 0x1 bytes, and 0x1 bytes appearing in the elements escaped as 0x1
+ * and 0x2 bytes. The list is terminated with a final delimiter, with no bytes following it.
+ *
+ * @since 2.0.0
+ * @param <E>
+ *          list element type.
+ */
+public class SequenceLexicoder<E> extends AbstractLexicoder<List<E>> {
+
+  private static final byte[] EMPTY_ELEMENT = new byte[0];
+  private final Lexicoder<E> elementLexicoder;
+
+  /**
+   * Primary constructor.
+   *
+   * @param elementLexicoder
+   *          Lexicoder to apply to elements.
+   */
+  public SequenceLexicoder(final Lexicoder<E> elementLexicoder) {
+    this.elementLexicoder = requireNonNull(elementLexicoder, "elementLexicoder");
+  }
+
+  /**
+   * {@inheritDoc}
+   *
+   * @return a byte array containing the concatenation of each element in the list encoded.
+   */
+  @Override
+  public byte[] encode(final List<E> v) {
+    final byte[][] encElements = new byte[v.size() + 1][];
+    int index = 0;
+    for (final E element : v) {
+      encElements[index++] = escape(elementLexicoder.encode(element));
+    }
+    encElements[v.size()] = EMPTY_ELEMENT;
+    return concat(encElements);
+  }
+
+  @Override
+  protected List<E> decodeUnchecked(final byte[] b, final int offset, final int len) {
+    final byte[][] escapedElements = split(b, offset, len);
+    assert escapedElements.length
 
 Review comment:
   assertions may not be enabled (they typically aren't). Should use IllegalArgumentException instead; could use Guava's `Preconditions.checkArgument()`.

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