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ByteStructIterator xref
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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  package org.apache.giraph.utils;
19  
20  import java.io.IOException;
21  import java.util.Iterator;
22  import org.apache.hadoop.io.Writable;
23  
24  /**
25   * This iterator is designed to deserialize a byte array on the fly to
26   * provide new copies of writable objects when desired.  It does not reuse
27   * objects, and instead creates a new one for every next().
28   *
29   * @param <T> Type that extends Writable that will be iterated
30   */
31  public abstract class ByteStructIterator<T extends Writable> implements
32      Iterator<T> {
33    /** Data input */
34    protected final ExtendedDataInput extendedDataInput;
35  
36    /**
37     * Wrap ExtendedDataInput in ByteArrayIterator
38     *
39     * @param extendedDataInput ExtendedDataInput
40     */
41    public ByteStructIterator(ExtendedDataInput extendedDataInput) {
42      this.extendedDataInput = extendedDataInput;
43    }
44  
45    @Override
46    public boolean hasNext() {
47      return !extendedDataInput.endOfInput();
48    }
49  
50    @Override
51    public T next() {
52      T writable = createWritable();
53      try {
54        writable.readFields(extendedDataInput);
55      } catch (IOException e) {
56        throw new IllegalStateException("next: readFields got IOException", e);
57      }
58      return writable;
59    }
60  
61    @Override
62    public void remove() {
63      throw new UnsupportedOperationException("remove: Not supported");
64    }
65  
66    /**
67     * Must be able to create the writable object
68     *
69     * @return New writable
70     */
71    protected abstract T createWritable();
72  }