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 <T>. 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 <S>. All computations are performed on the 039 * promoted data type <S>. There is a conversion method 040 * {@link ColumnInterpreter#castToReturnType(Object)} which takes a <T> type and returns a 041 * <S> type. The AggregateIm>lementation uses PB messages to initialize the user's 042 * ColumnInterpreter implementation, and for sending the responses back to AggregationClient. 043 * <p> 044 * <T> Cell value data type<br> 045 * <S> Promoted data type<br> 046 * <P> PB message that is used to transport initializer specific bytes<br> 047 * <Q> PB message that is used to transport Cell (<T>) instance<br> 048 * <R> PB message that is used to transport Promoted (<S>) 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>> 0 if l1 > l2 or l1 is not null and l2 is null.</li> 083 * <li>< 0 if l1 < 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 <S> data values. Not providing the divide method that takes 090 * two <S> 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}