java.lang.Object java.nio.charset.CharsetEncoder
public abstract class CharsetEncoder
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 then
Invoke the
flush
method so that the encoder can flush any internal state to the output buffer.
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
flush
and
reset
methods.
Instances of this class are not safe for use by multiple concurrent threads.
Each invocation of the
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.
Constructor Summary | |
---|---|
protected |
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 | |
---|---|
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. |
Charset |
charset
() Returns the charset that created this encoder. |
ByteBuffer |
encode
(
CharBuffer
in) Convenience method that encodes the remaining content of a single input character buffer into a newly-allocated byte buffer. |
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. |
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 |
implReset
() 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. |
CodingErrorAction |
malformedInputAction
() Returns this encoder's current action for malformed-input errors. |
float |
maxBytesPerChar
() Returns the maximum number of bytes that will be produced for each character of input. |
CharsetEncoder |
onMalformedInput
(
CodingErrorAction
newAction) Changes this encoder's action for malformed-input errors. |
CharsetEncoder |
onUnmappableCharacter
(
CodingErrorAction
newAction) Changes this encoder's action for unmappable-character errors. |
byte[] |
replacement
() Returns this encoder's replacement value. |
CharsetEncoder |
replaceWith
(byte[] newReplacement) Changes this encoder's replacement value. |
CharsetEncoder |
reset
() Resets this encoder, clearing any internal state. |
CodingErrorAction |
unmappableCharacterAction
() Returns this encoder's current action for unmappable-character errors. |
Methods inherited from class java.lang. Object |
---|
clone , equals , finalize , getClass , hashCode , notify , notifyAll , toString , wait , wait , wait |
Constructor Detail |
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protected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar, byte[] replacement)
protected CharsetEncoder(Charset cs, float averageBytesPerChar, float maxBytesPerChar)
Method Detail |
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public final Charset charset()
public final byte[] replacement()
public final CharsetEncoder replaceWith(byte[] newReplacement)
This method invokes the implReplaceWith method, passing the new replacement, after checking that the new replacement is acceptable.
protected 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.
public 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.
public CodingErrorAction malformedInputAction()
public final CharsetEncoder onMalformedInput(CodingErrorAction newAction)
This method invokes the implOnMalformedInput method, passing the new action.
protected 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.
public CodingErrorAction unmappableCharacterAction()
public final CharsetEncoder onUnmappableCharacter(CodingErrorAction newAction)
This method invokes the implOnUnmappableCharacter method, passing the new action.
protected 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.
public 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 are no characters remaining and the invoker has no further input then the encoding operation is complete. Otherwise there is insufficient input for the operation to proceed, so this method should be invoked again with further input.
CoderResult.OVERFLOW indicates that the output buffer is full. This method should be invoked again with a non-full 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.
public 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 .
This method invokes the implFlush method to perform the actual flushing operation.
protected 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.
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
a
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.
public 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
a
encoding operation is already in progress.
public 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.
public 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.