org.apache.hadoop.hbase.coprocessor.ColumnInterpreter Maven / Gradle / Ivy
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package org.apache.hadoop.hbase.coprocessor;
import com.google.protobuf.Message;
import java.io.IOException;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.yetus.audience.InterfaceAudience;
import org.apache.yetus.audience.InterfaceStability;
/**
* Defines how value for specific column is interpreted and provides utility methods like compare,
* add, multiply etc for them. Takes column family, column qualifier and return the cell value. Its
* concrete implementation should handle null case gracefully. Refer to
* {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter} for an example.
*
* Takes two generic parameters and three Message parameters. The cell value type of the interpreter
* is <T>. During some computations like sum, average, the return type can be different than
* the cell value data type, for eg, sum of int cell values might overflow in case of a int result,
* we should use Long for its result. Therefore, this class mandates to use a different (promoted)
* data type for result of these computations <S>. All computations are performed on the
* promoted data type <S>. There is a conversion method
* {@link ColumnInterpreter#castToReturnType(Object)} which takes a <T> type and returns a
* <S> type. The AggregateIm>lementation uses PB messages to initialize the user's
* ColumnInterpreter implementation, and for sending the responses back to AggregationClient.
*
* <T> Cell value data type
* <S> Promoted data type
* <P> PB message that is used to transport initializer specific bytes
* <Q> PB message that is used to transport Cell (<T>) instance
* <R> PB message that is used to transport Promoted (<S>) instance
*/
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.COPROC)
@InterfaceStability.Evolving
public abstract class ColumnInterpreter {
/** Returns value of type T */
public abstract T getValue(byte[] colFamily, byte[] colQualifier, Cell c) throws IOException;
/** Returns sum or non null value among (if either of them is null); otherwise returns a null. */
public abstract S add(S l1, S l2);
/**
* returns the maximum value for this type T
*/
public abstract T getMaxValue();
public abstract T getMinValue();
/** Returns multiplication */
public abstract S multiply(S o1, S o2);
/** Returns increment */
public abstract S increment(S o);
/**
* provides casting opportunity between the data types.
*/
public abstract S castToReturnType(T o);
/**
* This takes care if either of arguments are null. returns 0 if they are equal or both are null;
*
* - > 0 if l1 > l2 or l1 is not null and l2 is null.
* - < 0 if l1 < l2 or l1 is null and l2 is not null.
*
*/
public abstract int compare(final T l1, final T l2);
/**
* used for computing average of <S> data values. Not providing the divide method that takes
* two <S> values as it is not needed as of now.
*/
public abstract double divideForAvg(S o, Long l);
/**
* This method should return any additional data that is needed on the server side to construct
* the ColumnInterpreter. The server will pass this to the {@link #initialize} method. If there is
* no ColumnInterpreter specific data (for e.g.,
* {@link org.apache.hadoop.hbase.client.coprocessor.LongColumnInterpreter}) then null should be
* returned.
* @return the PB message
*/
public abstract P getRequestData();
/**
* This method should initialize any field(s) of the ColumnInterpreter with a parsing of the
* passed message bytes (used on the server side).
*/
public abstract void initialize(P msg);
/**
* This method gets the PB message corresponding to the cell type
* @return the PB message for the cell-type instance
*/
public abstract Q getProtoForCellType(T t);
/**
* This method gets the PB message corresponding to the cell type
* @return the cell-type instance from the PB message
*/
public abstract T getCellValueFromProto(Q q);
/**
* This method gets the PB message corresponding to the promoted type
* @return the PB message for the promoted-type instance
*/
public abstract R getProtoForPromotedType(S s);
/**
* This method gets the promoted type from the proto message
* @return the promoted-type instance from the PB message
*/
public abstract S getPromotedValueFromProto(R r);
/**
* The response message comes as type S. This will convert/cast it to T. In some sense, performs
* the opposite of {@link #castToReturnType(Object)}
*/
public abstract T castToCellType(S response);
}