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1   /*
2    *
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *     http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   */
19  package org.apache.hadoop.hbase.filter;
20  
21  import java.util.ArrayList;
22  
23  import org.apache.hadoop.hbase.classification.InterfaceAudience;
24  import org.apache.hadoop.hbase.classification.InterfaceStability;
25  import org.apache.hadoop.hbase.Cell;
26  import org.apache.hadoop.hbase.exceptions.DeserializationException;
27  import org.apache.hadoop.hbase.protobuf.generated.FilterProtos;
28  
29  import com.google.common.base.Preconditions;
30  import com.google.protobuf.InvalidProtocolBufferException;
31  
32  /**
33   * A filter that will only return the first KV from each row.
34   * <p>
35   * This filter can be used to more efficiently perform row count operations.
36   */
37  @InterfaceAudience.Public
38  @InterfaceStability.Stable
39  public class FirstKeyOnlyFilter extends FilterBase {
40    private boolean foundKV = false;
41  
42    public FirstKeyOnlyFilter() {
43    }
44  
45    public void reset() {
46      foundKV = false;
47    }
48  
49    @Override
50    public ReturnCode filterKeyValue(Cell v) {
51      if(foundKV) return ReturnCode.NEXT_ROW;
52      foundKV = true;
53      return ReturnCode.INCLUDE;
54    }
55  
56    public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
57      Preconditions.checkArgument(filterArguments.size() == 0,
58                                  "Expected 0 but got: %s", filterArguments.size());
59      return new FirstKeyOnlyFilter();
60    }
61  
62    /**
63     * @return true if first KV has been found.
64     */
65    protected boolean hasFoundKV() {
66      return this.foundKV;
67    }
68  
69    /**
70     *
71     * @param value update {@link #foundKV} flag with value.
72     */
73    protected void setFoundKV(boolean value) {
74      this.foundKV = value;
75    }
76  
77    /**
78     * @return The filter serialized using pb
79     */
80    public byte [] toByteArray() {
81      FilterProtos.FirstKeyOnlyFilter.Builder builder =
82        FilterProtos.FirstKeyOnlyFilter.newBuilder();
83      return builder.build().toByteArray();
84    }
85  
86    /**
87     * @param pbBytes A pb serialized {@link FirstKeyOnlyFilter} instance
88     * @return An instance of {@link FirstKeyOnlyFilter} made from <code>bytes</code>
89     * @throws org.apache.hadoop.hbase.exceptions.DeserializationException
90     * @see #toByteArray
91     */
92    public static FirstKeyOnlyFilter parseFrom(final byte [] pbBytes)
93    throws DeserializationException {
94      // There is nothing to deserialize.  Why do this at all?
95      try {
96        FilterProtos.FirstKeyOnlyFilter.parseFrom(pbBytes);
97      } catch (InvalidProtocolBufferException e) {
98        throw new DeserializationException(e);
99      }
100     // Just return a new instance.
101     return new FirstKeyOnlyFilter();
102   }
103 
104   /**
105    * @param other
106    * @return true if and only if the fields of the filter that are serialized
107    * are equal to the corresponding fields in other.  Used for testing.
108    */
109   boolean areSerializedFieldsEqual(Filter o) {
110     if (o == this) return true;
111     if (!(o instanceof FirstKeyOnlyFilter)) return false;
112 
113     return true;
114   }
115 }