Class CharsetEncoder
The input character sequence is provided in a character buffer or a series of such buffers. The output byte sequence is written to a byte buffer or a series of such buffers. An encoder should always be used by making the following sequence of method invocations, hereinafter referred to as an encoding operation:
Reset the encoder via the
reset
method, unless it has not been used before;Invoke the
encode
method zero or more times, as long as additional input may be available, passingfalse
for theendOfInput
argument and filling the input buffer and flushing the output buffer between invocations;Invoke the
encode
method one final time, passingtrue
for theendOfInput
argument; and thenInvoke the
flush
method so that the encoder can flush any internal state to the output buffer.
encode
method will encode as many
characters as possible from the input buffer, writing the resulting bytes
to the output buffer. The encode
method returns when more
input is required, when there is not enough room in the output buffer, or
when an encoding error has occurred. In each case a CoderResult
object is returned to describe the reason for termination. An invoker can
examine this object and fill the input buffer, flush the output buffer, or
attempt to recover from an encoding error, as appropriate, and try again.
There are two general types of encoding errors. If the input character sequence is not a legal sixteen-bit Unicode sequence then the input is considered malformed. If the input character sequence is legal but cannot be mapped to a valid byte sequence in the given charset then an unmappable character has been encountered.
How an encoding error is handled depends upon the action requested for
that type of error, which is described by an instance of the CodingErrorAction
class. The possible error actions are to ignore the erroneous input, report the error to the invoker via
the returned CoderResult
object, or replace the erroneous input with the current value of the
replacement byte array. The replacement
is initially set to the encoder's default replacement, which often
(but not always) has the initial value {
(byte)'?'
}
;
its value may be changed via the replaceWith
method.
The default action for malformed-input and unmappable-character errors
is to report them. The
malformed-input error action may be changed via the onMalformedInput
method; the
unmappable-character action may be changed via the onUnmappableCharacter
method.
This class is designed to handle many of the details of the encoding
process, including the implementation of error actions. An encoder for a
specific charset, which is a concrete subclass of this class, need only
implement the abstract encodeLoop
method, which
encapsulates the basic encoding loop. A subclass that maintains internal
state should, additionally, override the implFlush
and
implReset
methods.
Instances of this class are not safe for use by multiple concurrent threads.
- Since:
- 1.4
- See Also:
-
Constructor Summary
ModifierConstructorDescriptionprotected
CharsetEncoder
(Charset cs, float averageBytesPerChar, float maxBytesPerChar) Initializes a new encoder.protected
CharsetEncoder
(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement) Initializes a new encoder. -
Method Summary
Modifier and TypeMethodDescriptionfinal float
Returns the average number of bytes that will be produced for each character of input.boolean
canEncode
(char c) Tells whether or not this encoder can encode the given character.boolean
Tells whether or not this encoder can encode the given character sequence.final Charset
charset()
Returns the charset that created this encoder.final ByteBuffer
encode
(CharBuffer in) Convenience method that encodes the remaining content of a single input character buffer into a newly-allocated byte buffer.final CoderResult
encode
(CharBuffer in, ByteBuffer out, boolean endOfInput) Encodes as many characters as possible from the given input buffer, writing the results to the given output buffer.protected abstract CoderResult
encodeLoop
(CharBuffer in, ByteBuffer out) Encodes one or more characters into one or more bytes.final CoderResult
flush
(ByteBuffer out) Flushes this encoder.protected CoderResult
implFlush
(ByteBuffer out) Flushes this encoder.protected void
implOnMalformedInput
(CodingErrorAction newAction) Reports a change to this encoder's malformed-input action.protected void
implOnUnmappableCharacter
(CodingErrorAction newAction) Reports a change to this encoder's unmappable-character action.protected void
implReplaceWith
(byte[] newReplacement) Reports a change to this encoder's replacement value.protected void
Resets this encoder, clearing any charset-specific internal state.boolean
isLegalReplacement
(byte[] repl) Tells whether or not the given byte array is a legal replacement value for this encoder.Returns this encoder's current action for malformed-input errors.final float
Returns the maximum number of bytes that will be produced for each character of input.final CharsetEncoder
onMalformedInput
(CodingErrorAction newAction) Changes this encoder's action for malformed-input errors.final CharsetEncoder
onUnmappableCharacter
(CodingErrorAction newAction) Changes this encoder's action for unmappable-character errors.final byte[]
Returns this encoder's replacement value.final CharsetEncoder
replaceWith
(byte[] newReplacement) Changes this encoder's replacement value.final CharsetEncoder
reset()
Resets this encoder, clearing any internal state.Returns this encoder's current action for unmappable-character errors.
-
Constructor Details
-
CharsetEncoder
protected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement) Initializes a new encoder. The new encoder will have the given bytes-per-char and replacement values.- Parameters:
cs
- The charset that created this encoderaverageBytesPerChar
- A positive float value indicating the expected number of bytes that will be produced for each input charactermaxBytesPerChar
- A positive float value indicating the maximum number of bytes that will be produced for each input characterreplacement
- The initial replacement; must not benull
, must have non-zero length, must not be longer than maxBytesPerChar, and must be legal- Throws:
IllegalArgumentException
- If the preconditions on the parameters do not hold
-
CharsetEncoder
Initializes a new encoder. The new encoder will have the given bytes-per-char values and its replacement will be the byte array{
(byte)'?'
}
.- Parameters:
cs
- The charset that created this encoderaverageBytesPerChar
- A positive float value indicating the expected number of bytes that will be produced for each input charactermaxBytesPerChar
- A positive float value indicating the maximum number of bytes that will be produced for each input character- Throws:
IllegalArgumentException
- If the preconditions on the parameters do not hold
-
-
Method Details
-
charset
Returns the charset that created this encoder.- Returns:
- This encoder's charset
-
replacement
public final byte[] replacement()Returns this encoder's replacement value.- Returns:
- This encoder's current replacement,
which is never
null
and is never empty
-
replaceWith
Changes this encoder's replacement value.This method invokes the
implReplaceWith
method, passing the new replacement, after checking that the new replacement is acceptable.- Parameters:
newReplacement
- The new replacement; must not benull
, must have non-zero length, must not be longer than the value returned by themaxBytesPerChar
method, and must belegal
- Returns:
- This encoder
- Throws:
IllegalArgumentException
- If the preconditions on the parameter do not hold
-
implReplaceWith
protected void implReplaceWith(byte[] newReplacement) Reports a change to this encoder's replacement value.The default implementation of this method does nothing. This method should be overridden by encoders that require notification of changes to the replacement.
- Parameters:
newReplacement
- The replacement value
-
isLegalReplacement
public boolean isLegalReplacement(byte[] repl) Tells whether or not the given byte array is a legal replacement value for this encoder.A replacement is legal if, and only if, it is a legal sequence of bytes in this encoder's charset; that is, it must be possible to decode the replacement into one or more sixteen-bit Unicode characters.
The default implementation of this method is not very efficient; it should generally be overridden to improve performance.
- Parameters:
repl
- The byte array to be tested- Returns:
true
if, and only if, the given byte array is a legal replacement value for this encoder
-
malformedInputAction
Returns this encoder's current action for malformed-input errors.- Returns:
- The current malformed-input action, which is never
null
-
onMalformedInput
Changes this encoder's action for malformed-input errors.This method invokes the
implOnMalformedInput
method, passing the new action.- Parameters:
newAction
- The new action; must not benull
- Returns:
- This encoder
- Throws:
IllegalArgumentException
- If the precondition on the parameter does not hold
-
implOnMalformedInput
Reports a change to this encoder's malformed-input action.The default implementation of this method does nothing. This method should be overridden by encoders that require notification of changes to the malformed-input action.
- Parameters:
newAction
- The new action
-
unmappableCharacterAction
Returns this encoder's current action for unmappable-character errors.- Returns:
- The current unmappable-character action, which is never
null
-
onUnmappableCharacter
Changes this encoder's action for unmappable-character errors.This method invokes the
implOnUnmappableCharacter
method, passing the new action.- Parameters:
newAction
- The new action; must not benull
- Returns:
- This encoder
- Throws:
IllegalArgumentException
- If the precondition on the parameter does not hold
-
implOnUnmappableCharacter
Reports a change to this encoder's unmappable-character action.The default implementation of this method does nothing. This method should be overridden by encoders that require notification of changes to the unmappable-character action.
- Parameters:
newAction
- The new action
-
averageBytesPerChar
public final float averageBytesPerChar()Returns the average number of bytes that will be produced for each character of input. This heuristic value may be used to estimate the size of the output buffer required for a given input sequence.- Returns:
- The average number of bytes produced per character of input
-
maxBytesPerChar
public final float maxBytesPerChar()Returns the maximum number of bytes that will be produced for each character of input. This value may be used to compute the worst-case size of the output buffer required for a given input sequence. This value accounts for any necessary content-independent prefix or suffix bytes, such as byte-order marks.- Returns:
- The maximum number of bytes that will be produced per character of input
-
encode
Encodes as many characters as possible from the given input buffer, writing the results to the given output buffer.The buffers are read from, and written to, starting at their current positions. At most
in.remaining()
characters will be read and at mostout.remaining()
bytes will be written. The buffers' positions will be advanced to reflect the characters read and the bytes written, but their marks and limits will not be modified.In addition to reading characters from the input buffer and writing bytes to the output buffer, this method returns a
CoderResult
object to describe its reason for termination:CoderResult.UNDERFLOW
indicates that as much of the input buffer as possible has been encoded. If there is no further input then the invoker can proceed to the next step of the encoding operation. Otherwise this method should be invoked again with further input.CoderResult.OVERFLOW
indicates that there is insufficient space in the output buffer to encode any more characters. This method should be invoked again with an output buffer that has more remaining bytes. This is typically done by draining any encoded bytes from the output buffer.A malformed-input result indicates that a malformed-input error has been detected. The malformed characters begin at the input buffer's (possibly incremented) position; the number of malformed characters may be determined by invoking the result object's
length
method. This case applies only if the malformed action of this encoder isCodingErrorAction.REPORT
; otherwise the malformed input will be ignored or replaced, as requested.An unmappable-character result indicates that an unmappable-character error has been detected. The characters that encode the unmappable character begin at the input buffer's (possibly incremented) position; the number of such characters may be determined by invoking the result object's
length
method. This case applies only if the unmappable action of this encoder isCodingErrorAction.REPORT
; otherwise the unmappable character will be ignored or replaced, as requested.
The
endOfInput
parameter advises this method as to whether the invoker can provide further input beyond that contained in the given input buffer. If there is a possibility of providing additional input then the invoker should passfalse
for this parameter; if there is no possibility of providing further input then the invoker should passtrue
. It is not erroneous, and in fact it is quite common, to passfalse
in one invocation and later discover that no further input was actually available. It is critical, however, that the final invocation of this method in a sequence of invocations always passtrue
so that any remaining unencoded input will be treated as being malformed.This method works by invoking the
encodeLoop
method, interpreting its results, handling error conditions, and reinvoking it as necessary.- Parameters:
in
- The input character bufferout
- The output byte bufferendOfInput
-true
if, and only if, the invoker can provide no additional input characters beyond those in the given buffer- Returns:
- A coder-result object describing the reason for termination
- Throws:
IllegalStateException
- If an encoding operation is already in progress and the previous step was an invocation neither of thereset
method, nor of this method with a value offalse
for theendOfInput
parameter, nor of this method with a value oftrue
for theendOfInput
parameter but a return value indicating an incomplete encoding operationCoderMalfunctionError
- If an invocation of the encodeLoop method threw an unexpected exception
-
flush
Flushes this encoder.Some encoders maintain internal state and may need to write some final bytes to the output buffer once the overall input sequence has been read.
Any additional output is written to the output buffer beginning at its current position. At most
out.remaining()
bytes will be written. The buffer's position will be advanced appropriately, but its mark and limit will not be modified.If this method completes successfully then it returns
CoderResult.UNDERFLOW
. If there is insufficient room in the output buffer then it returnsCoderResult.OVERFLOW
. If this happens then this method must be invoked again, with an output buffer that has more room, in order to complete the current encoding operation.If this encoder has already been flushed then invoking this method has no effect.
This method invokes the
implFlush
method to perform the actual flushing operation.- Parameters:
out
- The output byte buffer- Returns:
- A coder-result object, either
CoderResult.UNDERFLOW
orCoderResult.OVERFLOW
- Throws:
IllegalStateException
- If the previous step of the current encoding operation was an invocation neither of theflush
method nor of the three-argumentencode
method with a value oftrue
for theendOfInput
parameter
-
implFlush
Flushes this encoder.The default implementation of this method does nothing, and always returns
CoderResult.UNDERFLOW
. This method should be overridden by encoders that may need to write final bytes to the output buffer once the entire input sequence has been read.- Parameters:
out
- The output byte buffer- Returns:
- A coder-result object, either
CoderResult.UNDERFLOW
orCoderResult.OVERFLOW
-
reset
Resets this encoder, clearing any internal state.This method resets charset-independent state and also invokes the
implReset
method in order to perform any charset-specific reset actions.- Returns:
- This encoder
-
implReset
protected void implReset()Resets this encoder, clearing any charset-specific internal state.The default implementation of this method does nothing. This method should be overridden by encoders that maintain internal state.
-
encodeLoop
Encodes one or more characters into one or more bytes.This method encapsulates the basic encoding loop, encoding as many characters as possible until it either runs out of input, runs out of room in the output buffer, or encounters an encoding error. This method is invoked by the
encode
method, which handles result interpretation and error recovery.The buffers are read from, and written to, starting at their current positions. At most
in.remaining()
characters will be read, and at mostout.remaining()
bytes will be written. The buffers' positions will be advanced to reflect the characters read and the bytes written, but their marks and limits will not be modified.This method returns a
CoderResult
object to describe its reason for termination, in the same manner as theencode
method. Most implementations of this method will handle encoding errors by returning an appropriate result object for interpretation by theencode
method. An optimized implementation may instead examine the relevant error action and implement that action itself.An implementation of this method may perform arbitrary lookahead by returning
CoderResult.UNDERFLOW
until it receives sufficient input.- Parameters:
in
- The input character bufferout
- The output byte buffer- Returns:
- A coder-result object describing the reason for termination
-
encode
Convenience method that encodes the remaining content of a single input character buffer into a newly-allocated byte buffer.This method implements an entire encoding operation; that is, it resets this encoder, then it encodes the characters in the given character buffer, and finally it flushes this encoder. This method should therefore not be invoked if an encoding operation is already in progress.
- Parameters:
in
- The input character buffer- Returns:
- A newly-allocated byte buffer containing the result of the encoding operation. The buffer's position will be zero and its limit will follow the last byte written.
- Throws:
IllegalStateException
- If an encoding operation is already in progressMalformedInputException
- If the character sequence starting at the input buffer's current position is not a legal sixteen-bit Unicode sequence and the current malformed-input action isCodingErrorAction.REPORT
UnmappableCharacterException
- If the character sequence starting at the input buffer's current position cannot be mapped to an equivalent byte sequence and the current unmappable-character action isCodingErrorAction.REPORT
CharacterCodingException
-MalformedInputException
if the character sequence starting at the input buffer's current position is not a legal sixteen-bit Unicode sequence and the current malformed-input action isCodingErrorAction.REPORT
;UnmappableCharacterException
if the character sequence starting at the input buffer's current position cannot be mapped to an equivalent byte sequence and the current unmappable-character action isCodingErrorAction.REPORT
OutOfMemoryError
- If the output byte buffer for the requested size of the input character buffer cannot be allocated
-
canEncode
public boolean canEncode(char c) Tells whether or not this encoder can encode the given character.This method returns
false
if the given character is a surrogate character; such characters can be interpreted only when they are members of a pair consisting of a high surrogate followed by a low surrogate. ThecanEncode(CharSequence)
method may be used to test whether or not a character sequence can be encoded.This method may modify this encoder's state; it should therefore not be invoked if an encoding operation is already in progress.
The default implementation of this method is not very efficient; it should generally be overridden to improve performance.
- Parameters:
c
- The given character- Returns:
true
if, and only if, this encoder can encode the given character- Throws:
IllegalStateException
- If an encoding operation is already in progress
-
canEncode
Tells whether or not this encoder can encode the given character sequence.If this method returns
false
for a particular character sequence then more information about why the sequence cannot be encoded may be obtained by performing a full encoding operation.This method may modify this encoder's state; it should therefore not be invoked if an encoding operation is already in progress.
The default implementation of this method is not very efficient; it should generally be overridden to improve performance.
- Parameters:
cs
- The given character sequence- Returns:
true
if, and only if, this encoder can encode the given character without throwing any exceptions and without performing any replacements- Throws:
IllegalStateException
- If an encoding operation is already in progress
-