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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 org.apache.hadoop.hbase.KeyValue;
23  
24  import java.io.DataInput;
25  import java.io.DataOutput;
26  import java.io.IOException;
27  import java.util.List;
28  import java.util.ArrayList;
29  
30  import com.google.common.base.Preconditions;
31  /**
32   * Implementation of Filter interface that limits results to a specific page
33   * size. It terminates scanning once the number of filter-passed rows is >
34   * the given page size.
35   * <p>
36   * Note that this filter cannot guarantee that the number of results returned
37   * to a client are <= page size. This is because the filter is applied
38   * separately on different region servers. It does however optimize the scan of
39   * individual HRegions by making sure that the page size is never exceeded
40   * locally.
41   */
42  public class PageFilter extends FilterBase {
43    private long pageSize = Long.MAX_VALUE;
44    private int rowsAccepted = 0;
45  
46    /**
47     * Default constructor, filters nothing. Required though for RPC
48     * deserialization.
49     */
50    public PageFilter() {
51      super();
52    }
53  
54    /**
55     * Constructor that takes a maximum page size.
56     *
57     * @param pageSize Maximum result size.
58     */
59    public PageFilter(final long pageSize) {
60      Preconditions.checkArgument(pageSize >= 0, "must be positive %s", pageSize);
61      this.pageSize = pageSize;
62    }
63  
64    public long getPageSize() {
65      return pageSize;
66    }
67  
68    public boolean filterAllRemaining() {
69      return this.rowsAccepted >= this.pageSize;
70    }
71  
72    public boolean filterRow() {
73      this.rowsAccepted++;
74      return this.rowsAccepted > this.pageSize;
75    }
76  
77    public static Filter createFilterFromArguments(ArrayList<byte []> filterArguments) {
78      Preconditions.checkArgument(filterArguments.size() == 1,
79                                  "Expected 1 but got: %s", filterArguments.size());
80      long pageSize = ParseFilter.convertByteArrayToLong(filterArguments.get(0));
81      return new PageFilter(pageSize);
82    }
83  
84    public void readFields(final DataInput in) throws IOException {
85      this.pageSize = in.readLong();
86    }
87  
88    public void write(final DataOutput out) throws IOException {
89      out.writeLong(pageSize);
90    }
91  
92    @Override
93    public String toString() {
94      return this.getClass().getSimpleName() + " " + this.pageSize;
95    }
96  }