Import code from internal repository to git

java/com/google/domain/registry/mapreduce/ConcatenatingInput.java

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+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed 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 com.google.domain.registry.mapreduce;
+
+import com.google.appengine.tools.mapreduce.Input;
+import com.google.appengine.tools.mapreduce.InputReader;
+import com.google.appengine.tools.mapreduce.inputs.ConcatenatingInputReader;
+import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.ListMultimap;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * A MapReduce {@link Input} adapter that joins multiple inputs.
+ *
+ * @param <T> input type
+ */
+public class ConcatenatingInput<T> extends Input<T> {
+
+  private static final long serialVersionUID = 1225981408139437077L;
+
+  private final Set<? extends Input<? extends T>> inputs;
+  private final int numShards;
+
+  public ConcatenatingInput(Iterable<? extends Input<? extends T>> inputs, int numShards) {
+    this.inputs = ImmutableSet.copyOf(inputs);
+    this.numShards = numShards;
+  }
+
+  @Override
+  public List<InputReader<T>> createReaders() throws IOException {
+    ListMultimap<Integer, InputReader<T>> shards = ArrayListMultimap.create();
+    int i = 0;
+    for (Input<? extends T> input : inputs) {
+      for (InputReader<? extends T> reader : input.createReaders()) {
+        // Covariant cast is safe because an InputReader<I> only outputs I and never consumes it.
+        @SuppressWarnings("unchecked")
+        InputReader<T> typedReader = (InputReader<T>) reader;
+        shards.put(i % numShards, typedReader);
+        i++;
+      }
+    }
+    ImmutableList.Builder<InputReader<T>> concatenatingReaders = new ImmutableList.Builder<>();
+    for (Collection<InputReader<T>> shard : shards.asMap().values()) {
+      concatenatingReaders.add(new ConcatenatingInputReader<>(ImmutableList.copyOf(shard)));
+    }
+    return concatenatingReaders.build();
+  }
+}