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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  
19  package org.apache.hadoop.hbase.codec;
20  
21  import java.io.IOException;
22  
23  import org.apache.hadoop.classification.InterfaceAudience;
24  import org.apache.hadoop.classification.InterfaceStability;
25  import org.apache.hadoop.hbase.KeyValue;
26  
27  /**
28   * Accepts a stream of KeyValues. This can be used to anywhere KeyValues need to be written out, but
29   * currently it is only used for serializing WALEdits. This could be backed by a List<KeyValue>, but
30   * more efficient implementations will append results to a byte[] to eliminate overhead, and
31   * possibly encode the underlying data further.
32   * <p>
33   * To read the data back, use a corresponding {@link Decoder}
34   * @see Decoder
35   */
36  @InterfaceAudience.Private
37  @InterfaceStability.Evolving
38  public interface Encoder {
39    /**
40     * Implementation must copy the entire state of the cell. If the written cell is modified
41     * immediately after the write method returns, the modifications must have absolutely no effect on
42     * the copy of the cell that was added in the write.
43     * @param cell cell to serialize
44     * @throws IOException
45     */
46    void write(KeyValue cell) throws IOException;
47  
48    /**
49     * Let the implementation decide what to do.  Usually means writing accumulated data into a
50     * byte[] that can then be read from the implementation to be sent to disk, put in the block
51     * cache, or sent over the network.
52     * @throws IOException
53     */
54    void flush() throws IOException;
55  }