public abstract class CharsetEncoder extends Object
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 then
Invoke 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.
| Modifier | Constructor | Description |
|---|---|---|
protected |
Initializes a new encoder. |
|
protected |
Initializes a new encoder. |
| Modifier and Type | Method | Description |
|---|---|---|
final float |
averageBytesPerChar() |
Returns the average number of bytes that will be produced for each character of input. |
boolean |
canEncode |
Tells whether or not this encoder can encode the given character. |
boolean |
canEncode |
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 |
Convenience method that encodes the remaining content of a single input character buffer into a newly-allocated byte buffer. |
final CoderResult |
encode |
Encodes as many characters as possible from the given input buffer, writing the results to the given output buffer. |
protected abstract CoderResult |
encodeLoop |
Encodes one or more characters into one or more bytes. |
final CoderResult |
flush |
Flushes this encoder. |
protected CoderResult |
implFlush |
Flushes this encoder. |
protected void |
implOnMalformedInput |
Reports a change to this encoder's malformed-input action. |
protected void |
implOnUnmappableCharacter |
Reports a change to this encoder's unmappable-character action. |
protected void |
implReplaceWith |
Reports a change to this encoder's replacement value. |
protected void |
implReset() |
Resets this encoder, clearing any charset-specific internal state. |
boolean |
isLegalReplacement |
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 |
Changes this encoder's action for malformed-input errors. |
final CharsetEncoder |
onUnmappableCharacter |
Changes this encoder's action for unmappable-character errors. |
final byte[] |
replacement() |
Returns this encoder's replacement value. |
final CharsetEncoder |
replaceWith |
Changes 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 CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement)
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 be null, must have non-zero length, must not be longer than maxBytesPerChar, and must be legal
IllegalArgumentException - If the preconditions on the parameters do not holdprotected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar)
{ (byte)'?' }.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 characterIllegalArgumentException - If the preconditions on the parameters do not holdpublic final Charset charset()
public final byte[] replacement()
null and is never emptypublic final CharsetEncoder replaceWith(byte[] newReplacement)
This method invokes the implReplaceWith method, passing the new replacement, after checking that the new replacement is acceptable.
newReplacement - 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
IllegalArgumentException - If the preconditions on the parameter do not holdprotected void implReplaceWith(byte[] newReplacement)
The default implementation of this method does nothing. This method should be overridden by encoders that require notification of changes to the replacement.
newReplacement - The replacement valuepublic boolean isLegalReplacement(byte[] repl)
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.
repl - The byte array to be testedtrue if, and only if, the given byte array is a legal replacement value for this encoderpublic CodingErrorAction malformedInputAction()
null
public final CharsetEncoder onMalformedInput(CodingErrorAction newAction)
This method invokes the implOnMalformedInput method, passing the new action.
newAction - The new action; must not be null
IllegalArgumentException - If the precondition on the parameter does not holdprotected void implOnMalformedInput(CodingErrorAction newAction)
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.
newAction - The new actionpublic CodingErrorAction unmappableCharacterAction()
null
public final CharsetEncoder onUnmappableCharacter(CodingErrorAction newAction)
This method invokes the implOnUnmappableCharacter method, passing the new action.
newAction - The new action; must not be null
IllegalArgumentException - If the precondition on the parameter does not holdprotected void implOnUnmappableCharacter(CodingErrorAction newAction)
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.
newAction - The new actionpublic final float averageBytesPerChar()
public final float maxBytesPerChar()
public final CoderResult encode(CharBuffer in, ByteBuffer out, boolean endOfInput)
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 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 is CodingErrorAction.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 is CodingErrorAction.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.
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 bufferIllegalStateException - 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 operationCoderMalfunctionError - If an invocation of the encodeLoop method threw an unexpected exceptionpublic final CoderResult flush(ByteBuffer out)
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.
out - The output byte bufferCoderResult.UNDERFLOW or CoderResult.OVERFLOW
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 parameterprotected CoderResult implFlush(ByteBuffer out)
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.
out - The output byte bufferCoderResult.UNDERFLOW or CoderResult.OVERFLOW
public final CharsetEncoder reset()
This method resets charset-independent state and also invokes the implReset method in order to perform any charset-specific reset actions.
protected void implReset()
The default implementation of this method does nothing. This method should be overridden by encoders that maintain internal state.
protected abstract CoderResult encodeLoop(CharBuffer in, ByteBuffer out)
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.
in - The input character bufferout - The output byte bufferpublic final ByteBuffer encode(CharBuffer in) throws CharacterCodingException
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.
in - The input character bufferIllegalStateException - 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 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 - 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
OutOfMemoryError - If the output byte buffer for the requested size of the input character buffer cannot be allocatedpublic boolean canEncode(char c)
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.
c - The given charactertrue if, and only if, this encoder can encode the given characterIllegalStateException - If an encoding operation is already in progresspublic boolean canEncode(CharSequence cs)
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.
cs - The given character sequencetrue if, and only if, this encoder can encode the given character without throwing any exceptions and without performing any replacementsIllegalStateException - If an encoding operation is already in progress
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