View Javadoc

1   /*
2    * Copyright 2010 The Apache Software Foundation
3    *
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *     http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing, software
15   * distributed under the License is distributed on an "AS IS" BASIS,
16   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
17   * See the License for the specific language governing permissions and
18   * limitations under the License.
19   */
20  package org.apache.hadoop.hbase.filter;
21  
22  import org.apache.hadoop.hbase.KeyValue;
23  
24  import java.io.DataOutput;
25  import java.io.IOException;
26  import java.io.DataInput;
27  import java.util.List;
28  
29  /**
30   * A filter that will only return the first KV from each row.
31   * <p>
32   * This filter can be used to more efficiently perform row count operations.
33   */
34  public class FirstKeyOnlyFilter extends FilterBase {
35    private boolean foundKV = false;
36  
37    public FirstKeyOnlyFilter() {
38    }
39  
40    public void reset() {
41      foundKV = false;
42    }
43  
44    public ReturnCode filterKeyValue(KeyValue v) {
45      if(foundKV) return ReturnCode.NEXT_ROW;
46      foundKV = true;
47      return ReturnCode.INCLUDE;
48    }
49  
50    public void write(DataOutput out) throws IOException {
51    }
52  
53    public void readFields(DataInput in) throws IOException {
54    }
55  }