001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.coprocessor;
019
020import java.io.IOException;
021import org.apache.hadoop.hbase.Cell;
022import org.apache.hadoop.hbase.HBaseInterfaceAudience;
023import org.apache.yetus.audience.InterfaceAudience;
024import org.apache.yetus.audience.InterfaceStability;
025
026import org.apache.hbase.thirdparty.com.google.protobuf.Message;
027
028/**
029 * Defines how value for specific column is interpreted and provides utility methods like compare,
030 * add, multiply etc for them. Takes column family, column qualifier and return the cell value. Its
031 * concrete implementation should handle null case gracefully. Refer to
032 * {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter} for an example.
033 * <p>
034 * Takes two generic parameters and three Message parameters. The cell value type of the interpreter
035 * is &lt;T&gt;. During some computations like sum, average, the return type can be different than
036 * the cell value data type, for eg, sum of int cell values might overflow in case of a int result,
037 * we should use Long for its result. Therefore, this class mandates to use a different (promoted)
038 * data type for result of these computations &lt;S&gt;. All computations are performed on the
039 * promoted data type &lt;S&gt;. There is a conversion method
040 * {@link ColumnInterpreter#castToReturnType(Object)} which takes a &lt;T&gt; type and returns a
041 * &lt;S&gt; type. The AggregateIm&gt;lementation uses PB messages to initialize the user's
042 * ColumnInterpreter implementation, and for sending the responses back to AggregationClient.
043 * <p>
044 * &lt;T&gt; Cell value data type<br>
045 * &lt;S&gt; Promoted data type<br>
046 * &lt;P&gt; PB message that is used to transport initializer specific bytes<br>
047 * &lt;Q&gt; PB message that is used to transport Cell (&lt;T&gt;) instance<br>
048 * &lt;R&gt; PB message that is used to transport Promoted (&lt;S&gt;) instance
049 */
050@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
051@InterfaceStability.Evolving
052public abstract class ColumnInterpreter<T, S, P extends Message, Q extends Message,
053  R extends Message> {
054
055  /** Returns value of type T */
056  public abstract T getValue(byte[] colFamily, byte[] colQualifier, Cell c) throws IOException;
057
058  /** Returns sum or non null value among (if either of them is null); otherwise returns a null. */
059  public abstract S add(S l1, S l2);
060
061  /**
062   * returns the maximum value for this type T
063   */
064  public abstract T getMaxValue();
065
066  public abstract T getMinValue();
067
068  /** Returns multiplication */
069  public abstract S multiply(S o1, S o2);
070
071  /** Returns increment */
072  public abstract S increment(S o);
073
074  /**
075   * provides casting opportunity between the data types.
076   */
077  public abstract S castToReturnType(T o);
078
079  /**
080   * This takes care if either of arguments are null. returns 0 if they are equal or both are null;
081   * <ul>
082   * <li>&gt; 0 if l1 &gt; l2 or l1 is not null and l2 is null.</li>
083   * <li>&lt; 0 if l1 &lt; l2 or l1 is null and l2 is not null.</li>
084   * </ul>
085   */
086  public abstract int compare(final T l1, final T l2);
087
088  /**
089   * used for computing average of &lt;S&gt; data values. Not providing the divide method that takes
090   * two &lt;S&gt; values as it is not needed as of now.
091   */
092  public abstract double divideForAvg(S o, Long l);
093
094  /**
095   * This method should return any additional data that is needed on the server side to construct
096   * the ColumnInterpreter. The server will pass this to the {@link #initialize} method. If there is
097   * no ColumnInterpreter specific data (for e.g.,
098   * {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter}) then null should be
099   * returned.
100   * @return the PB message
101   */
102  public abstract P getRequestData();
103
104  /**
105   * This method should initialize any field(s) of the ColumnInterpreter with a parsing of the
106   * passed message bytes (used on the server side).
107   */
108  public abstract void initialize(P msg);
109
110  /**
111   * This method gets the PB message corresponding to the cell type
112   * @return the PB message for the cell-type instance
113   */
114  public abstract Q getProtoForCellType(T t);
115
116  /**
117   * This method gets the PB message corresponding to the cell type
118   * @return the cell-type instance from the PB message
119   */
120  public abstract T getCellValueFromProto(Q q);
121
122  /**
123   * This method gets the PB message corresponding to the promoted type
124   * @return the PB message for the promoted-type instance
125   */
126  public abstract R getProtoForPromotedType(S s);
127
128  /**
129   * This method gets the promoted type from the proto message
130   * @return the promoted-type instance from the PB message
131   */
132  public abstract S getPromotedValueFromProto(R r);
133
134  /**
135   * The response message comes as type S. This will convert/cast it to T. In some sense, performs
136   * the opposite of {@link #castToReturnType(Object)}
137   */
138  public abstract T castToCellType(S response);
139}