public interface IKeyBuilder extends ISortKeyBuilder<Object>, IManagedByteArray
Interface for building up variable
unsigned byte keys from
one or more primitive data types values and/or Unicode strings. An instance
of this interface may be
reset() and reused to encode a series of
A sort key is an unsigned byte that preserves the total order of the
original data. Sort keys may potentially be formed from multiple fields but
field markers do not appear within the resulting sort key. While the original
values can be extracted from sort keys (this is true of all the fixed length
fields, such as int, long, float, or double) they can not be extracted from
Unicode variable length fields (the collation ordering for a Unicode string
depends on the
Locale, the collation strength, and the decomposition
mode and is a non-reversable operation).
Factory methods are defined by
KeyBuilder for obtaining instances of
this interface that optionally support Unicode. Instances may be created for
Locale, collation strength, decomposition mode, etc.
The ICU library supports generation of compressed Unicode sort keys and is
used by default when available. The JDK
java.text package also
supports the generation of Unicode sort keys, but it does NOT produce
compressed sort keys. The resulting sort keys are therefore (a) incompatible
with those produced by the ICU library and (b) much larger than those
produced by the ICU library.
Support for Unicode MAY be disabled using
KeyBuilder.Options.COLLATOR, by using
KeyBuilder.newInstance() or another factory method that does not
enable Unicode support, or by using one of the
constructors that does not support Unicode.
Multi-field keys in which variable length fields are embedded within the key
present a special problem. Any run of fixed length fields can be compared as
unsigned bytes. Likewise, any any key with a fixed length prefix (including
zero) but a variable length field in its tail can also be compared directly
as unsigned bytes. However, the introduction of a variable length field
into any non-terminal position in a multi-field key must be handled specially
since simple concatenation of the field keys will NOT produce the correct
total ordering. (This is why SQL requires that text fields compare as if they
were padded out with ASCII blanks (0x20) to some maximum length for the
field.) A utility method exists specifically for this purpose - see
appendText(String, boolean, boolean).
|Modifier and Type||Field and Description|
The maximum length of a variable length text field is
|Modifier and Type||Method and Description|
Appends a byte - the byte is treated as an
Appends an array of bytes - the bytes are treated as
Append len bytes starting at off in a to the key buffer - the bytes are treated as
Appends a double precision floating point value by first converting it into a signed long integer using
Appends a single precision floating point value by first converting it into a signed integer using
Appends a signed integer to the key by first converting it to a lexiographic ordering as an unsigned integer and then appending it into the buffer as 4 bytes using a big-endian order.
Appends a signed long integer to the key by first converting it to a lexiographic ordering as an unsigned long integer and then appending it into the buffer as 8 bytes using a big-endian order.
Append the value to the buffer, encoding it as appropriate based on the class of the object.
Appends a signed short integer to the key by first converting it to a two-complete representation supporting unsigned byte comparison and then appending it into the buffer as 2 bytes using a big-endian order.
Encodes a Unicode string using the configured
Appends the UUID to the key using the MSB and then the LSB (this preserves the natural order imposed by
Encodes a unicode string by assuming that its contents are ASCII characters.
Append an unsigned zero byte to the key.
Converts the signed byte to an unsigned byte and appends it to the key.
Encodes a variable length text field into the buffer.
The backing byte WILL be transparently replaced if the buffer capacity is extended.
Return the encoded key.
The length of the slice is number of bytes written onto the backing byte.
The offset of the slice into the backing byte is always zero.
Reset the key length to zero before building another key.
An alias for
static final int maxlen
Note: This restriction only applies to multi-field keys where the text field appears in a non-terminal position within the key - that is as encoded by . When a text field appears in such a non-terminal position trailing pad characters are used to maintain lexiographic ordering over the multi-field key.
reset(). The length of the slice in the
IByteArraySlice.len()has different semantics for some concrete implementations.
ByteArrayBuffer.len()always returns the capacity of the backing byte while
ByteArrayBuffer.pos()returns the #of bytes written onto the backing buffer. In contrast,
KeyBuilder.len()is always the #of bytes written onto the backing buffer.
Note that keys are donated to the btree so it is important to allocate new keys when running in the same process space. When using a network api, the api provides the necessary decoupling.
getKey(). Return a copy of the data in the slice.
IKeyBuilder append(String s)
KeyBuilder.Options.COLLATORand appends the resulting sort key to the buffer (without a trailing nul byte).
SuccessorUtil.successor(String) of a string is formed
by appending a trailing
nul character. However, since
IDENTICAL appears to be required to differentiate between
a string and its successor (with the trailing
character), you MUST form the sort key first and then its successor (by
appending a trailing
nul). Failure to follow this pattern
will lead to the successor of the key comparing as EQUAL to the key. For
IKeyBuilder keyBuilder = ...; String s = "foo"; byte fromKey = keyBuilder.reset().append( s ); // right. byte toKey = keyBuilder.reset().append( s ).appendNul(); // wrong! byte toKey = keyBuilder.reset().append( s+"\0" );
s- A string.
UnsupportedOperationException- if Unicode is not supported.
FIXME update the javadoc further to speak to handling of multi-field keys.
IKeyBuilder appendText(String text, boolean unicode, boolean successor)
maxlencharacters. The sort keys for strings that differ after truncation solely in the #of trailing
#padcharacters will be identical (trailing pad characters are implicit out to
Note: Trailing pad characters are normalized to a representation as a single pad character (1 byte) followed by the #of actual or implied trailing pad characters represented as an unsigned short integer (2 bytes). This technique serves to keep multi-field keys with embedded variable length text fields aligned such that the field following a variable length text field does not bleed into the lexiographic ordering of the variable length text field.
Note: While the ASCII encoding happens to use one byte for each character that is NOT true of the Unicode encoding. The space requirements for the Unicode encoding depend on the text, the Locale, the collator strength, and the collator decomposition mode.
Note: The successor option is designed to encapsulate some
trickiness around forming the successor of a variable length text field
embedded in a multi-field key. In particular, simply appending a
nul byte will NOT work (it works fine when the text field
is the last field in the key or when it is the only component in the
key). This approach breaks encapsulation of the field boundaries such
that the resulting "successor" is actually ordered before the original
key. This happens because you introduce a 0x0 byte right on the boundary
of the next field, effectively causing the next field to have a smaller
value. Consider the following example (in hex) where "|" represents the
end of the "text" field:
ab cd | 12if you compute the successor by appending a nul byte to the text field you get
ab cd | 00 12which is ordered before the original key!
text- The text.
unicode- When true the text is interpreted as Unicode according to the
KeyBuilder.Options.COLLATORoption. Otherwise it is interpreted as ASCII.
successor- When true, the successor of the text will be encoded. Otherwise the text will be encoded.
trueiff Unicode is supported by this object (returns
falseif only ASCII support is configured).
IKeyBuilder appendASCII(String s)
Note: This method is potentially much faster than the Unicode aware
append(String). However, this method is NOT unicode aware and
non-ASCII characters will not be encoded correctly. This method MUST NOT
be mixed with keys whose corresponding component is encoded by the
unicode aware methods, e.g.,
s- A String containing US-ASCII characters.
IKeyBuilder append(byte b)
IKeyBuilder append(byte a)
IKeyBuilder append(byte a, int off, int len)
IKeyBuilder append(double d)
Double.doubleToLongBits(double), converting that values into a twos-complement number and then appending the bytes in big-endian order into the key buffer.
Note: this converts -0d and +0d to the same key.
d- The double-precision floating point value.
IKeyBuilder append(float f)
Float.floatToIntBits(float)converting that values into a twos-complement number and then appending the bytes in big-endian order into the key buffer.
Note: this converts -0f and +0f to the same key.
f- The single-precision floating point value.
IKeyBuilder append(UUID uuid)
uuid- The UUID.
IKeyBuilder append(long v)
IKeyBuilder append(int v)
IKeyBuilder append(short v)
IKeyBuilder appendSigned(byte v)
v- The signed byte.
IKeyBuilder append(BigInteger i)
BigIntegerinto an unsigned byte and append it into the key buffer.
IKeyBuilder append(BigDecimal d)
BigDecimalinto an unsigned byte and append it into the key buffer.
IKeyBuilder append(Object val)
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