CharsetDecoder (Java Platform SE 6)

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java.nio.charset
class CharsetDecoder

java.lang.Object
  java.nio.charset.CharsetDecoder

Most common way to construct:

Charset charset = …;

CharsetDecoder decoder = charset.newDecoder();

Based on 63 examples

public abstract class CharsetDecoder
extends Object

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 {@link #reset reset} method, unless it has not been used before;

Invoke the {@link #decode 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;

Invoke the {@link #decode decode} method one final time, passing true for the endOfInput argument; and then

Invoke the {@link #flush flush} method so that the decoder can flush any internal state to the output buffer.

Each invocation of the {@link #decode decode} method will decode as many bytes as possible from the input buffer, writing the resulting characters to the output buffer. The {@link #decode 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 {@link 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.

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 {@link CodingErrorAction} class. The possible error actions are to {@link CodingErrorAction#IGNORE ignore} the erroneous input, {@link CodingErrorAction#REPORTreport} the error to the invoker via the returned {@link CoderResult} object, or {@link CodingErrorAction#REPLACEreplace} 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 {@link #replaceWith(java.lang.String) replaceWith} method.

The default action for malformed-input and unmappable-character errors is to {@link CodingErrorAction#REPORTreport} them. The malformed-input error action may be changed via the {@link #onMalformedInput(CodingErrorAction) onMalformedInput} method; the unmappable-character action may be changed via the {@link #onUnmappableCharacter(CodingErrorAction) onUnmappableCharacter} method.

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 {@link #decodeLoop decodeLoop} method, which encapsulates the basic decoding loop. A subclass that maintains internal state should, additionally, override the {@link #implFlush implFlush} and {@link #implReset implReset} methods.

Instances of this class are not safe for use by multiple concurrent threads.



	
		Constructor Summary
	
	
		protected
		CharsetDecoder(Charset cs, float averageCharsPerByte, float maxCharsPerByte)
			
          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(ByteBuffer in)
			
          Convenience method that decodes the remaining content of a single input
 byte buffer into a newly-allocated character buffer.
		
	
	
		 CoderResult
		decode(ByteBuffer in, CharBuffer out, boolean endOfInput)
			
          Decodes as many bytes as possible from the given input buffer,
 writing the results to the given output buffer.
		
	
	
		protected abstract CoderResult
		decodeLoop(ByteBuffer in, CharBuffer out)
			
          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(CharBuffer out)
			
          Flushes this decoder.
		
	
	
		protected CoderResult
		implFlush(CharBuffer out)
			
          Flushes this decoder.
		
	
	
		protected void
		implOnMalformedInput(CodingErrorAction newAction)
			
          Reports a change to this decoder's malformed-input action.
		
	
	
		protected void
		implOnUnmappableCharacter(CodingErrorAction newAction)
			
          Reports a change to this decoder's unmappable-character action.
		
	
	
		protected void
		implReplaceWith(String newReplacement)
			
          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(CodingErrorAction newAction)
			
          Changes this decoder's action for malformed-input errors.
		
	
	
		 CharsetDecoder
		onUnmappableCharacter(CodingErrorAction newAction)
			
          Changes this decoder's action for unmappable-character errors.
		
	
	
		 String
		replacement()
			
          Returns this decoder's replacement value.
		
	
	
		 CharsetDecoder
		replaceWith(String newReplacement)
			
          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, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait 





Constructor Detail


CharsetDecoder
protected CharsetDecoder(Charset cs,
                         float averageCharsPerByte,
                         float maxCharsPerByte)


Initializes a new decoder.  The new decoder will have the given
 chars-per-byte values and its replacement will be the
 string "\uFFFD". 


Parameters:
cs
averageCharsPerByte - A positive float value indicating the expected number of
         characters that will be produced for each input byte
maxCharsPerByte - A positive float value indicating the maximum number of
         characters that will be produced for each input byte







Method Detail


averageCharsPerByte
public final float averageCharsPerByte()


Returns the average number of characters that will be produced for each
 byte 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 characters produced
          per byte of input



charset
public final Charset charset()


Returns the charset that created this decoder.  


Returns:
This decoder's charset



decode
public final CharBuffer decode(ByteBuffer in)
                        throws CharacterCodingException


Convenience method that decodes the remaining content of a single input
 byte buffer into a newly-allocated character buffer.

  This method implements an entire decoding
 operation; that is, it resets this decoder, then it decodes the
 bytes in the given byte buffer, and finally it flushes this
 decoder.  This method should therefore not be invoked if a decoding
 operation is already in progress.  


Parameters:
in - The input byte buffer
Returns:
A newly-allocated character buffer containing the result of the
         decoding operation.  The buffer's position will be zero and its
         limit will follow the last character written.
Throws:
CharacterCodingException




decode
public final CoderResult decode(ByteBuffer in,
                                CharBuffer out,
                                boolean endOfInput)

Constructor Summary
`protected`	`CharsetDecoder(Charset cs, float averageCharsPerByte, float maxCharsPerByte)` 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(ByteBuffer in)` Convenience method that decodes the remaining content of a single input byte buffer into a newly-allocated character buffer.
`CoderResult`	`decode(ByteBuffer in, CharBuffer out, boolean endOfInput)` Decodes as many bytes as possible from the given input buffer, writing the results to the given output buffer.
`protected abstract CoderResult`	`decodeLoop(ByteBuffer in, CharBuffer out)` 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(CharBuffer out)` Flushes this decoder.
`protected CoderResult`	`implFlush(CharBuffer out)` Flushes this decoder.
`protected void`	`implOnMalformedInput(CodingErrorAction newAction)` Reports a change to this decoder's malformed-input action.
`protected void`	`implOnUnmappableCharacter(CodingErrorAction newAction)` Reports a change to this decoder's unmappable-character action.
`protected void`	`implReplaceWith(String newReplacement)` 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(CodingErrorAction newAction)` Changes this decoder's action for malformed-input errors.
`CharsetDecoder`	`onUnmappableCharacter(CodingErrorAction newAction)` Changes this decoder's action for unmappable-character errors.
`String`	`replacement()` Returns this decoder's replacement value.
`CharsetDecoder`	`replaceWith(String newReplacement)` 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, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`


Decodes as many bytes 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 {@link Buffer#remaining in.remaining()} bytes
 will be read and at most {@link Buffer#remaining 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 {@link CoderResult}
 object to describe its reason for termination:



    {@link CoderResult#UNDERFLOW} indicates that as much of the
   input buffer as possible has been decoded.  If there is no further
   input then the invoker can proceed to the next step of the
   decoding operation.  Otherwise this method
   should be invoked again with further input.  

    {@link CoderResult#OVERFLOW} indicates that there is
   insufficient space in the output buffer to decode any more bytes.
   This method should be invoked again with an output buffer that has
   more {@linkplain Buffer#remaining remaining} characters. This is
   typically done by draining any decoded characters from the output
   buffer.

A {@link CoderResult#malformedForLengthmalformed-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 {@link CoderResult#length() length} method. This case applies only if the {@link #onMalformedInputmalformed action} of this decoder is {@link CodingErrorAction#REPORT}; otherwise the malformed input will be ignored or replaced, as requested.

An {@link CoderResult#unmappableForLengthunmappable-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 {@link CoderResult#length() length} method. This case applies only if the {@link #onUnmappableCharacterunmappable action} of this decoder is {@link CodingErrorAction#REPORT}; otherwise the unmappable character will be ignored or replaced, as requested.



 In any case, if this method is to be reinvoked in the same decoding
 operation then care should be taken to preserve any bytes remaining
 in the input buffer so that they are available to the next invocation.

  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 {@link #decodeLoop decodeLoop}
 method, interpreting its results, handling error conditions, and
 reinvoking it as necessary.  


Parameters:
in - The input byte buffer
out - The output character buffer
endOfInput - true if, and only if, the invoker can provide no
         additional input bytes beyond those in the given buffer
Returns:
A coder-result object describing the reason for termination



decodeLoop
protected abstract CoderResult decodeLoop(ByteBuffer in,
                                          CharBuffer out)


Decodes one or more bytes into one or more characters.

  This method encapsulates the basic decoding loop, decoding as many
 bytes as possible until it either runs out of input, runs out of room
 in the output buffer, or encounters a decoding error.  This method is
 invoked by the {@link #decode decode} method, which handles result
 interpretation and error recovery.

 
 The buffers are read from, and written to, starting at their current
 positions.  At most {@link Buffer#remaining in.remaining()} bytes
 will be read, and at most {@link Buffer#remaining 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.

 
 This method returns a {@link CoderResult} object to describe its
 reason for termination, in the same manner as the {@link #decode decode}
 method.  Most implementations of this method will handle decoding errors
 by returning an appropriate result object for interpretation by the
 {@link #decode decode} 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 {@link CoderResult#UNDERFLOW} until it receives sufficient
 input.  


Parameters:
in - The input byte buffer
out - The output character buffer
Returns:
A coder-result object describing the reason for termination



detectedCharset
public Charset detectedCharset()


Retrieves the charset that was detected by this
 decoder  (optional operation).

  If this decoder implements an auto-detecting charset then this
 method returns the actual charset once it has been detected.  After that
 point, this method returns the same value for the duration of the
 current decoding operation.  If not enough input bytes have yet been
 read to determine the actual charset then this method throws an {@link
 IllegalStateException}.

 
 The default implementation of this method always throws an {@link
 UnsupportedOperationException}; it should be overridden by
 auto-detecting decoders to return the appropriate value.  


Returns:
The charset detected by this auto-detecting decoder,
          or null if the charset has not yet been determined



flush
public final CoderResult flush(CharBuffer out)


Flushes this decoder.

  Some decoders maintain internal state and may need to write some
 final characters 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 {@link Buffer#remaining out.remaining()}
 characters 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 {@link
 CoderResult#UNDERFLOW}.  If there is insufficient room in the output
 buffer then it returns {@link 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 decoding
 operation.

 
 If this decoder has already been flushed then invoking this method
 has no effect.

 
 This method invokes the {@link #implFlush implFlush} method to
 perform the actual flushing operation.  


Parameters:
out - The output character buffer
Returns:
A coder-result object, either {@link CoderResult#UNDERFLOW} or
          {@link CoderResult#OVERFLOW}



implFlush
protected CoderResult implFlush(CharBuffer out)


Flushes this decoder.

  The default implementation of this method does nothing, and always
 returns {@link CoderResult#UNDERFLOW}.  This method should be overridden
 by decoders that may need to write final characters to the output buffer
 once the entire input sequence has been read. 


Parameters:
out - The output character buffer
Returns:
A coder-result object, either {@link CoderResult#UNDERFLOW} or
          {@link CoderResult#OVERFLOW}



implOnMalformedInput
protected void implOnMalformedInput(CodingErrorAction newAction)


Reports a change to this decoder's malformed-input action.

  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.  


Parameters:
newAction




implOnUnmappableCharacter
protected void implOnUnmappableCharacter(CodingErrorAction newAction)


Reports a change to this decoder's unmappable-character action.

  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.  


Parameters:
newAction




implReplaceWith
protected void implReplaceWith(String newReplacement)


Reports a change to this decoder's replacement value.

  The default implementation of this method does nothing.  This method
 should be overridden by decoders that require notification of changes to
 the replacement.  


Parameters:
newReplacement




implReset
protected void implReset()


Resets this decoder, clearing any charset-specific internal state.

  The default implementation of this method does nothing.  This method
 should be overridden by decoders that maintain internal state.  




isAutoDetecting
public boolean isAutoDetecting()


Tells whether or not this decoder implements an auto-detecting charset.

  The default implementation of this method always returns
 false; it should be overridden by auto-detecting decoders to
 return true.  


Returns:
true if, and only if, this decoder implements an
          auto-detecting charset



isCharsetDetected
public boolean isCharsetDetected()


Tells whether or not this decoder has yet detected a
 charset  (optional operation).

  If this decoder implements an auto-detecting charset then at a
 single point during a decoding operation this method may start returning
 true to indicate that a specific charset has been detected in
 the input byte sequence.  Once this occurs, the {@link #detectedCharset
 detectedCharset} method may be invoked to retrieve the detected charset.

 
 That this method returns false does not imply that no bytes
 have yet been decoded.  Some auto-detecting decoders are capable of
 decoding some, or even all, of an input byte sequence without fixing on
 a particular charset.

 
 The default implementation of this method always throws an {@link
 UnsupportedOperationException}; it should be overridden by
 auto-detecting decoders to return true once the input charset
 has been determined.  


Returns:
true if, and only if, this decoder has detected a
          specific charset



malformedInputAction
public CodingErrorAction malformedInputAction()


Returns this decoder's current action for malformed-input errors.  


Returns:
The current malformed-input action, which is never null



maxCharsPerByte
public final float maxCharsPerByte()


Returns the maximum number of characters that will be produced for each
 byte 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 characters that will be produced per
          byte of input



onMalformedInput
public final CharsetDecoder onMalformedInput(CodingErrorAction newAction)


Changes this decoder's action for malformed-input errors.  

  This method invokes the {@link #implOnMalformedInput
 implOnMalformedInput} method, passing the new action.  


Parameters:
newAction - The new action; must not be null
Returns:
This decoder



onUnmappableCharacter
public final CharsetDecoder onUnmappableCharacter(CodingErrorAction newAction)


Changes this decoder's action for unmappable-character errors.

  This method invokes the {@link #implOnUnmappableCharacter
 implOnUnmappableCharacter} method, passing the new action.  


Parameters:
newAction - The new action; must not be null
Returns:
This decoder



replacement
public final String replacement()


Returns this decoder's replacement value. 


Returns:
This decoder's current replacement,
          which is never null and is never empty



replaceWith
public final CharsetDecoder replaceWith(String newReplacement)


Changes this decoder's replacement value.

  This method invokes the {@link #implReplaceWith implReplaceWith}
 method, passing the new replacement, after checking that the new
 replacement is acceptable.  


Parameters:
newReplacement - The new replacement; must not be null
         and must have non-zero length
Returns:
This decoder



reset
public final CharsetDecoder reset()


Resets this decoder, clearing any internal state.

  This method resets charset-independent state and also invokes the
 {@link #implReset() implReset} method in order to perform any
 charset-specific reset actions.  


Returns:
This decoder



unmappableCharacterAction
public CodingErrorAction unmappableCharacterAction()


Returns this decoder's current action for unmappable-character errors.
 


Returns:
The current unmappable-character action, which is never
         null






	
	


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	This documentation differs from the official API.

	Jadeite adds extra features to the API including:
		variable font sizes,
		constructions examples,
		placeholders for classes and methods, and auto-generated “See Also” links.

	Additionally it is missing some items found in standard Javadoc documentation, including:
		generics type information,
		“Deprecated” tags and comments,
		“See Also” links,
		along with other minor differences.

	Please send any questions or feedback to bam@cs.cmu.edu.
This page displays the Jadeite version of the documention, which is derived from the offical documentation that contains this copyright notice:Copyright 2008 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.
The official Sun™ documentation can be found here at http://java.sun.com/javase/6/docs/api/.

java.nio.charsetclass CharsetDecoder

CharsetDecoder

averageCharsPerByte

charset

decode

decode

decodeLoop

detectedCharset

flush

implFlush

implOnMalformedInput

implOnUnmappableCharacter

implReplaceWith

implReset

isAutoDetecting

isCharsetDetected

malformedInputAction

maxCharsPerByte

onMalformedInput

onUnmappableCharacter

replacement

replaceWith

reset

unmappableCharacterAction

java.nio.charset
class CharsetDecoder