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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 java.io.DataInput;
23  import java.io.DataOutput;
24  import java.io.IOException;
25  import java.util.List;
26  
27  import org.apache.hadoop.hbase.KeyValue;
28  
29  /**
30   * A filter, based on the ColumnCountGetFilter, takes two arguments: limit and offset.
31   * This filter can be used for row-based indexing, where references to other tables are stored across many columns,
32   * in order to efficient lookups and paginated results for end users.
33   */
34  public class ColumnPaginationFilter extends FilterBase
35  {
36    private int limit = 0;
37    private int offset = 0;
38    private int count = 0;
39  
40      /**
41       * Used during serialization. Do not use.
42       */
43    public ColumnPaginationFilter()
44    {
45      super();
46    }
47  
48    public ColumnPaginationFilter(final int limit, final int offset)
49    {
50      this.limit = limit;
51      this.offset = offset;
52    }
53  
54    @Override
55    public ReturnCode filterKeyValue(KeyValue v)
56    {
57      if(count >= offset + limit)
58      {
59        return ReturnCode.NEXT_ROW;
60      }
61  
62      ReturnCode code = count < offset ? ReturnCode.SKIP : ReturnCode.INCLUDE;
63      count++;
64      return code;
65    }
66  
67    @Override
68    public void reset()
69    {
70      this.count = 0;
71    }
72  
73    public void readFields(DataInput in) throws IOException
74    {
75      this.limit = in.readInt();
76      this.offset = in.readInt();
77    }
78  
79    public void write(DataOutput out) throws IOException
80    {
81      out.writeInt(this.limit);
82      out.writeInt(this.offset);
83    }
84  }