An engine that can transform a sequence of sixteen-bit Unicode characters into a sequence of bytes in a specific charset.
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, passing false for the endOfInput argument and filling the input buffer and flushing the output buffer between invocations;Invoke the
encode
method one final time, passing true for the endOfInput 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 {@linkplain CodingErrorAction#IGNORE ignore} the erroneous input, {@linkplain CodingErrorAction#REPORT report} the error to the invoker via
the returned CoderResult
object, or {@linkplain CodingErrorAction#REPLACE
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 {@linkplain CodingErrorAction#REPORT 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.
Protected Constructor Summary
CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement)
Initializes a new encoder.
|
|
CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar)
Initializes a new encoder.
|
Public Method Summary
final float |
averageBytesPerChar()
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 |
canEncode(CharSequence cs)
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.
|
final CoderResult | |
boolean |
isLegalReplacement(byte[] repl)
Tells whether or not the given byte array is a legal replacement value
for this encoder.
|
CodingErrorAction |
malformedInputAction()
Returns this encoder's current action for malformed-input errors.
|
final float |
maxBytesPerChar()
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 CharsetEncoder |
replaceWith(byte[] newReplacement)
Changes this encoder's replacement value.
|
final byte[] |
replacement()
Returns this encoder's replacement value.
|
final CharsetEncoder |
reset()
Resets this encoder, clearing any internal state.
|
CodingErrorAction |
unmappableCharacterAction()
Returns this encoder's current action for unmappable-character errors.
|
Protected Method Summary
abstract CoderResult | |
CoderResult | |
void |
implOnMalformedInput(CodingErrorAction newAction)
Reports a change to this encoder's malformed-input action.
|
void |
implOnUnmappableCharacter(CodingErrorAction newAction)
Reports a change to this encoder's unmappable-character action.
|
void |
implReplaceWith(byte[] newReplacement)
Reports a change to this encoder's replacement value.
|
void |
implReset()
Resets this encoder, clearing any charset-specific internal state.
|
Inherited Method Summary
Protected Constructors
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 encoder |
---|---|
averageBytesPerChar | A positive float value indicating the expected number of bytes that will be produced for each input character |
maxBytesPerChar | A positive float value indicating the maximum number of bytes that will be produced for each input character |
replacement | The initial replacement; must not be null, must have non-zero length, must not be longer than maxBytesPerChar, and must be {@linkplain #isLegalReplacement legal} |
Throws
IllegalArgumentException | If the preconditions on the parameters do not hold |
---|
protected CharsetEncoder (Charset cs, float averageBytesPerChar, float maxBytesPerChar)
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 encoder |
---|---|
averageBytesPerChar | A positive float value indicating the expected number of bytes that will be produced for each input character |
maxBytesPerChar | 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 |
---|
Public Methods
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
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. The canEncode(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 |
---|
public boolean canEncode (CharSequence cs)
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 |
---|
public final Charset charset ()
Returns the charset that created this encoder.
Returns
- This encoder's charset
public final ByteBuffer encode (CharBuffer in)
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 progress |
---|---|
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
is CodingErrorAction.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 is CodingErrorAction.REPORT
|
CharacterCodingException |
public 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.
The buffers are read from, and written to, starting at their current
positions. At most in.remaining()
characters
will be read and at most out.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 {@linkplain Buffer#remaining remaining} bytes. This is typically done by draining any encoded bytes from the output buffer.A {@linkplain CoderResult#malformedForLength 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 {@linkplain #onMalformedInput malformed action} of this encoder isCodingErrorAction.REPORT
; otherwise the malformed input will be ignored or replaced, as requested.An {@linkplain CoderResult#unmappableForLength 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 {@linkplain #onUnmappableCharacter 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 pass false for this parameter; if there is no possibility of providing further input then the invoker should pass true. It is not erroneous, and in fact it is quite common, to pass false 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 pass true 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 buffer |
---|---|
out | The output byte buffer |
endOfInput | 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 the reset
method, nor of this method with a value of false for
the endOfInput parameter, nor of this method with a
value of true for the endOfInput parameter
but a return value indicating an incomplete encoding operation |
---|---|
CoderMalfunctionError | If an invocation of the encodeLoop method threw an unexpected exception |
public final CoderResult flush (ByteBuffer out)
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 returns CoderResult.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 the flush method nor of
the three-argument encode method
with a value of true for the endOfInput
parameter
|
---|
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
public CodingErrorAction malformedInputAction ()
Returns this encoder's current action for malformed-input errors.
Returns
- The current malformed-input action, which is never null
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.
Returns
- The maximum number of bytes that will be produced per character of input
public final CharsetEncoder onMalformedInput (CodingErrorAction newAction)
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 be null |
---|
Returns
- This encoder
Throws
IllegalArgumentException | If the precondition on the parameter does not hold |
---|
public final CharsetEncoder onUnmappableCharacter (CodingErrorAction newAction)
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 be null |
---|
Returns
- This encoder
Throws
IllegalArgumentException | If the precondition on the parameter does not hold |
---|
public final CharsetEncoder replaceWith (byte[] newReplacement)
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 replacement value
The new replacement; must not be null, must have
non-zero length, must not be longer than the value returned by
the maxBytesPerChar method, and
must be legal |
---|
Returns
- This encoder
Throws
IllegalArgumentException | If the preconditions on the parameter do not hold |
---|
public final byte[] replacement ()
Returns this encoder's replacement value.
Returns
- This encoder's current replacement, which is never null and is never empty
public final CharsetEncoder 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
public CodingErrorAction unmappableCharacterAction ()
Returns this encoder's current action for unmappable-character errors.
Returns
- The current unmappable-character action, which is never null
Protected Methods
protected abstract CoderResult encodeLoop (CharBuffer in, ByteBuffer out)
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 most out.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 the encode
method. Most implementations of this method will handle encoding errors
by returning an appropriate result object for interpretation by the
encode
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 buffer |
---|---|
out | The output byte buffer |
Returns
- A coder-result object describing the reason for termination
protected CoderResult implFlush (ByteBuffer out)
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
protected void implOnMalformedInput (CodingErrorAction newAction)
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 |
---|
protected void implOnUnmappableCharacter (CodingErrorAction newAction)
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 |
---|
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 |
---|
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.