Added in API level 1

CharsetDecoder

abstract class CharsetDecoder

kotlin.Any
↳	java.nio.charset.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:

1. Reset the decoder via the reset method, unless it has not been used before;
2. Invoke the #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;
3. Invoke the #decode method one final time, passing true for the endOfInput argument; and then
4. Invoke the flush method so that the decoder can flush any internal state to the output buffer.

Each invocation of the #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.

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 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.

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 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 decodeLoop method, which encapsulates the basic decoding 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.

Summary

Protected constructors
CharsetDecoder(cs: Charset!, averageCharsPerByte: Float, maxCharsPerByte: Float) Initializes a new decoder.

Public methods
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.
CoderResult!	decode(in: ByteBuffer!, out: CharBuffer!, endOfInput: Boolean) Decodes as many bytes as possible from the given input buffer, writing the results to the given output buffer.
CharBuffer!	decode(in: ByteBuffer!) Convenience method that decodes the remaining content of a single input byte buffer into a newly-allocated character buffer.
open Charset!	detectedCharset() Retrieves the charset that was detected by this decoder  (optional operation).
CoderResult!	flush(out: CharBuffer!) Flushes this decoder.
open Boolean	isAutoDetecting() Tells whether or not this decoder implements an auto-detecting charset.
open Boolean	isCharsetDetected() Tells whether or not this decoder has yet detected a charset  (optional operation).
open 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(newAction: CodingErrorAction!) Changes this decoder's action for malformed-input errors.
CharsetDecoder!	onUnmappableCharacter(newAction: CodingErrorAction!) Changes this decoder's action for unmappable-character errors.
CharsetDecoder!	replaceWith(newReplacement: String!) Changes this decoder's replacement value.
String!	replacement() Returns this decoder's replacement value.
CharsetDecoder!	reset() Resets this decoder, clearing any internal state.
open CodingErrorAction!	unmappableCharacterAction() Returns this decoder's current action for unmappable-character errors.

Protected methods
abstract CoderResult!	decodeLoop(in: ByteBuffer!, out: CharBuffer!) Decodes one or more bytes into one or more characters.
open CoderResult!	implFlush(out: CharBuffer!) Flushes this decoder.
open Unit	implOnMalformedInput(newAction: CodingErrorAction!) Reports a change to this decoder's malformed-input action.
open Unit	implOnUnmappableCharacter(newAction: CodingErrorAction!) Reports a change to this decoder's unmappable-character action.
open Unit	implReplaceWith(newReplacement: String!) Reports a change to this decoder's replacement value.
open Unit	implReset() Resets this decoder, clearing any charset-specific internal state.

Protected constructors

CharsetDecoder

Added in API level 1

protected CharsetDecoder(
    cs: Charset!, 
    averageCharsPerByte: Float, 
    maxCharsPerByte: Float)

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	Charset!: The charset that created this decoder
averageCharsPerByte	Float: A positive float value indicating the expected number of characters that will be produced for each input byte
maxCharsPerByte	Float: A positive float value indicating the maximum number of characters that will be produced for each input byte

Exceptions
java.lang.IllegalArgumentException	If the preconditions on the parameters do not hold

Public methods

averageCharsPerByte

Added in API level 1

fun averageCharsPerByte(): Float

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.

Return
Float	The average number of characters produced per byte of input

charset

Added in API level 1

fun charset(): Charset!

Returns the charset that created this decoder.

Return
Charset!	This decoder's charset

decode

Added in API level 1

fun decode(
    in: ByteBuffer!, 
    out: CharBuffer!, 
    endOfInput: Boolean
): CoderResult!

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 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 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.
• 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 remaining characters. This is typically done by draining any decoded characters from the 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 java.nio.charset.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 decodeLoop method, interpreting its results, handling error conditions, and reinvoking it as necessary.

Parameters
in	ByteBuffer!: The input byte buffer
out	CharBuffer!: The output character buffer
endOfInput	Boolean: true if, and only if, the invoker can provide no additional input bytes beyond those in the given buffer

Return
CoderResult!	A coder-result object describing the reason for termination

Exceptions
java.lang.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
java.nio.charset.CoderMalfunctionError	If an invocation of the decodeLoop method threw an unexpected exception
java.lang.NullPointerException	if input or output buffer is null

decode

Added in API level 1

fun decode(in: ByteBuffer!): CharBuffer!

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	ByteBuffer!: The input byte buffer

Return
CharBuffer!	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.

Exceptions
java.lang.IllegalStateException	If a decoding operation is already in progress
java.nio.charset.MalformedInputException	If the byte sequence starting at the input buffer's current position is not legal for this charset and the current malformed-input action is CodingErrorAction#REPORT
java.nio.charset.UnmappableCharacterException	If the byte sequence starting at the input buffer's current position cannot be mapped to an equivalent character sequence and the current unmappable-character action is java.nio.charset.CodingErrorAction#REPORT
java.nio.charset.CoderMalfunctionError	If an invocation of the decodeLoop method threw an unexpected exception
java.lang.NullPointerException	if input buffer is null

detectedCharset

Added in API level 1

open fun detectedCharset(): Charset!

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 IllegalStateException.

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

Return
Charset!	The charset detected by this auto-detecting decoder, or null if the charset has not yet been determined

Exceptions
java.lang.IllegalStateException	If insufficient bytes have been read to determine a charset
java.lang.UnsupportedOperationException	If this decoder does not implement an auto-detecting charset

flush

Added in API level 1

fun flush(out: CharBuffer!): CoderResult!

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 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 java.nio.charset.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 decoding operation.

If this decoder 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	CharBuffer!: The output character buffer

Return
CoderResult!	A coder-result object, either CoderResult#UNDERFLOW or CoderResult#OVERFLOW

Exceptions
java.lang.IllegalStateException	If the previous step of the current decoding operation was an invocation neither of the flush method nor of the three-argument decode method with a value of true for the endOfInput parameter

isAutoDetecting

Added in API level 1

open fun isAutoDetecting(): Boolean

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.

Return
Boolean	true if, and only if, this decoder implements an auto-detecting charset

isCharsetDetected

Added in API level 1

open fun isCharsetDetected(): Boolean

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 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 UnsupportedOperationException; it should be overridden by auto-detecting decoders to return true once the input charset has been determined.

Return
Boolean	true if, and only if, this decoder has detected a specific charset

Exceptions
java.lang.UnsupportedOperationException	If this decoder does not implement an auto-detecting charset

malformedInputAction

Added in API level 1

open fun malformedInputAction(): CodingErrorAction!

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

Return
CodingErrorAction!	The current malformed-input action, which is never null

maxCharsPerByte

Added in API level 1

fun maxCharsPerByte(): Float

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. This value accounts for any necessary content-independent prefix or suffix characters.

Return
Float	The maximum number of characters that will be produced per byte of input

onMalformedInput

Added in API level 1

fun onMalformedInput(newAction: CodingErrorAction!): CharsetDecoder!

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

This method invokes the implOnMalformedInput method, passing the new action.

Parameters
newAction	CodingErrorAction!: The new action; must not be null

Return
CharsetDecoder!	This decoder

Exceptions
java.lang.IllegalArgumentException	If the precondition on the parameter does not hold

onUnmappableCharacter

Added in API level 1

fun onUnmappableCharacter(newAction: CodingErrorAction!): CharsetDecoder!

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

This method invokes the implOnUnmappableCharacter method, passing the new action.

Parameters
newAction	CodingErrorAction!: The new action; must not be null

Return
CharsetDecoder!	This decoder

Exceptions
java.lang.IllegalArgumentException	If the precondition on the parameter does not hold

replaceWith

Added in API level 1

fun replaceWith(newReplacement: String!): CharsetDecoder!

Changes this decoder's replacement value.

This method invokes the implReplaceWith method, passing the new replacement, after checking that the new replacement is acceptable.

Parameters
newReplacement	String!: The new replacement; must not be null, must have non-zero length, and must not be longer than the value returned by the maxCharsPerByte method

Return
CharsetDecoder!	This decoder

Exceptions
java.lang.IllegalArgumentException	If the preconditions on the parameter do not hold

replacement

Added in API level 1

fun replacement(): String!

Returns this decoder's replacement value.

Return
String!	This decoder's current replacement, which is never null and is never empty

reset

Added in API level 1

fun reset(): CharsetDecoder!

Resets this decoder, 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.

Return
CharsetDecoder!	This decoder

unmappableCharacterAction

Added in API level 1

open fun unmappableCharacterAction(): CodingErrorAction!

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

Return
CodingErrorAction!	The current unmappable-character action, which is never null

Protected methods

decodeLoop

Added in API level 1

protected abstract fun decodeLoop(
    in: ByteBuffer!, 
    out: CharBuffer!
): CoderResult!

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 #decode 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() 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.

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

Parameters
in	ByteBuffer!: The input byte buffer
out	CharBuffer!: The output character buffer

Return
CoderResult!	A coder-result object describing the reason for termination

implFlush

Added in API level 1

protected open fun implFlush(out: CharBuffer!): CoderResult!

Flushes this decoder.

The default implementation of this method does nothing, and always returns 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	CharBuffer!: The output character buffer

Return
CoderResult!	A coder-result object, either CoderResult#UNDERFLOW or CoderResult#OVERFLOW

implOnMalformedInput

Added in API level 1

protected open fun implOnMalformedInput(newAction: CodingErrorAction!): Unit

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	CodingErrorAction!: The new action

implOnUnmappableCharacter

Added in API level 1

protected open fun implOnUnmappableCharacter(newAction: CodingErrorAction!): Unit

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	CodingErrorAction!: The new action

implReplaceWith

Added in API level 1

protected open fun implReplaceWith(newReplacement: String!): Unit

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	String!: The replacement value

implReset

Added in API level 1

protected open fun implReset(): Unit

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.