Package org.apache.druid.frame.field

Class StringFieldReader

java.lang.Object

org.apache.druid.frame.field.StringFieldReader

All Implemented Interfaces:

FieldReader

Direct Known Subclasses:

StringArrayFieldReader

public class StringFieldReader
extends Object
implements FieldReader

Reads fields written by StringFieldWriter or StringArrayFieldWriter. Strings are written in UTF8 and terminated by StringFieldWriter.VALUE_TERMINATOR. Note that this byte appears in valid UTF8 encodings if and only if the string contains a NUL (char 0). Therefore, this field writer cannot write out strings containing NUL characters. All rows are terminated by StringFieldWriter.ROW_TERMINATOR. Empty rows are represented in one byte: solely that StringFieldWriter.ROW_TERMINATOR. Rows that are null themselves (i.e., a null array) are represented as a StringFieldWriter.NULL_ROW followed by a StringFieldWriter.ROW_TERMINATOR. This encoding for null arrays is decoded by older readers as an empty array; null arrays are a feature that did not exist in earlier versions of the code. Null strings are stored as StringFieldWriter.NULL_BYTE. All other strings are prepended by StringFieldWriter.NOT_NULL_BYTE byte to differentiate them from nulls. This encoding allows the encoded data to be compared as bytes in a way that matches the behavior of StringDimensionHandler.DIMENSION_SELECTOR_COMPARATOR, except null and empty list are not considered equal.

Constructor Summary

Constructors

Modifier	Constructor	Description
	StringFieldReader()
protected	StringFieldReader(boolean asArray)	Create a string reader.

Method Summary

Modifier and Type	Method	Description
boolean	isComparable()	Whether this field is comparable.
boolean	isNull(org.apache.datasketches.memory.Memory memory, long position)	Whether the provided memory position points to a null value.
ColumnValueSelector<?>	makeColumnValueSelector(org.apache.datasketches.memory.Memory memory, ReadableFieldPointer fieldPointer)	Create a ColumnValueSelector backed by some memory and a moveable pointer.
DimensionSelector	makeDimensionSelector(org.apache.datasketches.memory.Memory memory, ReadableFieldPointer fieldPointer, ExtractionFn extractionFn)	Create a DimensionSelector backed by some memory and a moveable pointer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

StringFieldReader

public StringFieldReader()

StringFieldReader

protected StringFieldReader(boolean asArray)

Create a string reader.

Parameters:

asArray - if false, selectors from makeColumnValueSelector(org.apache.datasketches.memory.Memory, org.apache.druid.frame.field.ReadableFieldPointer) behave like ValueType.STRING selectors (potentially multi-value ones). If true, selectors from makeColumnValueSelector(org.apache.datasketches.memory.Memory, org.apache.druid.frame.field.ReadableFieldPointer) behave like string array selectors.

Method Detail

makeColumnValueSelector

public ColumnValueSelector<?> makeColumnValueSelector(org.apache.datasketches.memory.Memory memory,
                                                      ReadableFieldPointer fieldPointer)

Description copied from interface: FieldReader

Create a ColumnValueSelector backed by some memory and a moveable pointer.

Specified by:

makeColumnValueSelector in interface FieldReader

makeDimensionSelector

public DimensionSelector makeDimensionSelector(org.apache.datasketches.memory.Memory memory,
                                               ReadableFieldPointer fieldPointer,
                                               @Nullable
                                               ExtractionFn extractionFn)

Description copied from interface: FieldReader

Create a DimensionSelector backed by some memory and a moveable pointer.

Specified by:

makeDimensionSelector in interface FieldReader

isNull

public boolean isNull(org.apache.datasketches.memory.Memory memory,
                      long position)

Description copied from interface: FieldReader

Whether the provided memory position points to a null value.

Specified by:

isNull in interface FieldReader

isComparable

public boolean isComparable()

Description copied from interface: FieldReader

Whether this field is comparable. Comparable fields can be compared as unsigned bytes.

Specified by:

isComparable in interface FieldReader