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java.lang.Object![]()
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java.nio.charset.CharsetDecoder
public abstract class CharsetDecoder

An engine that can transform a sequence of bytes in a specific charset into a sequence of
sixteen-bit Unicode characters.
The input byte sequence is provided in a byte buffer or a series
of such buffers. The output character sequence is written to a character buffer
or a series of such buffers. A decoder should always be used by making
the following sequence of method invocations, hereinafter referred to as a
decoding operation:
Reset the decoder via the Invoke the Invoke the Invoke the There are two general types of decoding errors. If the input byte
sequence is not legal for this charset then the input is considered malformed. If
the input byte sequence is legal but cannot be mapped to a valid
Unicode character then an unmappable character has been encountered.
How a decoding error is handled depends upon the action requested for
that type of error, which is described by an instance of the The default action for malformed-input and unmappable-character errors
is to This class is designed to handle many of the details of the decoding
process, including the implementation of error actions. A decoder for a
specific charset, which is a concrete subclass of this class, need only
implement the abstract Instances of this class are not safe for use by multiple concurrent
threads.
Each invocation of the reset
method, unless it
has not been used before; decode
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; decode
method one final time, passing
true for the endOfInput argument; and then flush
method so that the decoder can
flush any internal state to the output buffer. decode
method will decode as many
bytes as possible from the input buffer, writing the resulting characters
to the output buffer. The decode
method returns when more
input is required, when there is not enough room in the output buffer, or
when a decoding 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 a decoding error, as appropriate, and try again.
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 string. The replacement
has the initial value "\uFFFD";
its value may be changed via the replaceWith
method.
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.
decodeLoop
method, which
encapsulates the basic decoding loop. A subclass that maintains internal
state should, additionally, override the flush
and reset
methods.
ByteBuffer
,
CharBuffer
,
Charset
,
CharsetEncoder

| Constructor Summary | |
|---|---|
protected |
CharsetDecoder
Initializes a new decoder. |
| Method Summary | |
|---|---|
float |
averageCharsPerByte
Returns the average number of characters that will be produced for each byte of input. |
Charset |
charset
Returns the charset that created this decoder. |
CharBuffer |
decode
Convenience method that decodes the remaining content of a single input byte buffer into a newly-allocated character buffer. |
CoderResult |
decode
Decodes as many bytes as possible from the given input buffer, writing the results to the given output buffer. |
protected abstract CoderResult |
decodeLoop
Decodes one or more bytes into one or more characters. |
Charset |
detectedCharset
Retrieves the charset that was detected by this decoder (optional operation). |
CoderResult |
flush
Flushes this decoder. |
protected CoderResult |
implFlush
Flushes this decoder. |
protected void |
implOnMalformedInput
Reports a change to this decoder's malformed-input action. |
protected void |
implOnUnmappableCharacter
Reports a change to this decoder's unmappable-character action. |
protected void |
implReplaceWith
Reports a change to this decoder's replacement value. |
protected void |
implReset
Resets this decoder, clearing any charset-specific internal state. |
boolean |
isAutoDetecting
Tells whether or not this decoder implements an auto-detecting charset. |
boolean |
isCharsetDetected
Tells whether or not this decoder has yet detected a charset (optional operation). |
CodingErrorAction |
malformedInputAction
Returns this decoder's current action for malformed-input errors. |
float |
maxCharsPerByte
Returns the maximum number of characters that will be produced for each byte of input. |
CharsetDecoder |
onMalformedInput
Changes this decoder's action for malformed-input errors. |
CharsetDecoder |
onUnmappableCharacter
Changes this decoder's action for unmappable-character errors. |
String |
replacement
Returns this decoder's replacement value. |
CharsetDecoder |
replaceWith
Changes this decoder's replacement value. |
CharsetDecoder |
reset
Resets this decoder, clearing any internal state. |
CodingErrorAction |
unmappableCharacterAction
Returns this decoder's current action for unmappable-character errors. |
Methods inherited from class java.lang.Object ![]() |
|---|
clone |
| Constructor Detail |
|---|

protected CharsetDecoder(Charset![]()
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cs, float averageCharsPerByte, float maxCharsPerByte)
averageCharsPerByte - A positive float value indicating the expected number of
characters that will be produced for each input bytemaxCharsPerByte - A positive float value indicating the maximum number of
characters that will be produced for each input byte
IllegalArgumentException

- If the preconditions on the parameters do not hold| Method Detail |
|---|

public final Charset![]()
![]()
charset()

public final String![]()
![]()
replacement()

public final CharsetDecoder![]()
![]()
replaceWith(String
![]()
![]()
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
and must have non-zero length
IllegalArgumentException

- If the preconditions on the parameter do not hold

protected void implReplaceWith(String![]()
![]()
newReplacement)
The default implementation of this method does nothing. This method should be overridden by decoders that require notification of changes to the replacement.
newReplacement -

public CodingErrorAction![]()
![]()
malformedInputAction()

public final CharsetDecoder![]()
![]()
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 hold

protected void implOnMalformedInput(CodingErrorAction![]()
![]()
newAction)
The default implementation of this method does nothing. This method should be overridden by decoders that require notification of changes to the malformed-input action.

public CodingErrorAction![]()
![]()
unmappableCharacterAction()

public final CharsetDecoder![]()
![]()
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 hold

protected void implOnUnmappableCharacter(CodingErrorAction![]()
![]()
newAction)
The default implementation of this method does nothing. This method should be overridden by decoders that require notification of changes to the unmappable-character action.

public final float averageCharsPerByte()

public final float maxCharsPerByte()

public final CoderResult![]()
![]()
decode(ByteBuffer
![]()
![]()
in, CharBuffer
![]()
![]()
out, boolean endOfInput)
The buffers are read from, and written to, starting at their current
positions. At most in.remaining()
bytes
will be read and at most out.remaining()
characters will be written. The buffers' positions will be advanced to
reflect the bytes read and the characters written, but their marks and
limits will not be modified.
In addition to reading bytes from the input buffer and writing
characters 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 decoded. If there are no bytes
remaining and the invoker has no further input then the decoding
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 bytes begin at the input
buffer's (possibly incremented) position; the number of malformed
bytes may be determined by invoking the result object's length
method. This case applies only if the
malformed action
of this decoder
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 bytes that
decode the unmappable character begin at the input buffer's (possibly
incremented) position; the number of such bytes may be determined
by invoking the result object's length
method. This case applies only if the unmappable action
of this decoder 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 undecoded input will be treated as being malformed.
This method works by invoking the decodeLoop
method, interpreting its results, handling error conditions, and
reinvoking it as necessary.
in - The input byte bufferout - The output character bufferendOfInput - true if, and only if, the invoker can provide no
additional input bytes beyond those in the given buffer
IllegalStateException

- If a decoding 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 decoding operation
CoderMalfunctionError

- If an invocation of the decodeLoop method threw
an unexpected exception

public final CoderResult![]()
![]()
flush(CharBuffer