java::io::CharsetDecoder Class Reference

Inheritance diagram for java::io::CharsetDecoder:

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java::io::CharsetCoderjava::lang::Object
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Collaboration diagram for java::io::CharsetDecoder:

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java::io::CharsetCoderjava::lang::Objectjava::lang::Stringjava::lang::Interfacejava::lang::ObjectRefjava::lang::Comparable
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List of all members.


Detailed Description

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 flush and reset methods.

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

Version:
1.37, 03/01/23
Author:
Mark Reinhold

JSR-51 Expert Group

Since:
1.4
See also:
ByteBuffer

CharBuffer

Charset

CharsetEncoder


Public Member Functions

Ref< CoderResultflush (Array< jchar > &out)
 Flushes this coder.
Ref< CoderResultdecode (Array< jbyte > &in, Array< jchar > &out, jboolean endOfInput)
 Decodes as many bytes as possible from the given input buffer, writing the results to the given output buffer.
Array< jchardecode (Array< jbyte > &in)
 Convenience method that decodes the remaining content of a single input byte buffer into a newly-allocated character buffer.

Protected Member Functions

 CharsetDecoder (const Ref< Charset > &cs, jfloat averageRatio, jfloat maxRatio, const String &replace="?")
 Initializes a new decoder.
virtual Ref
< CoderResult
implFlush (Array< jchar > &out)
 Flushes this coder.
virtual Ref
< CoderResult
decodeLoop (Array< jbyte > &in, Array< jchar > &out)=0
 Decodes one or more bytes into one or more characters.

Constructor & Destructor Documentation

java::io::CharsetDecoder::CharsetDecoder ( const Ref< Charset > &  cs,
jfloat  averageRatio,
jfloat  maxRatio,
const String replace = "?" 
) [protected]

Initializes a new decoder.

The new decoder will have the given chars-per-byte and replacement values.

Parameters:
averageRatio A positive float value indicating the expected number of characters that will be produced for each input byte
maxRatio A positive float value indicating the maximum number of characters that will be produced for each input byte
replacement The initial replacement; must not be null, must have non-zero length, must not be longer than maxRatio, and must be legal
Exceptions:
IllegalArgumentException  If the preconditions on the parameters do not hold


Member Function Documentation

Ref<CoderResult> java::io::CharsetDecoder::flush ( Array< jchar > &  out  ) 

Flushes this coder.

Some coders 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 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.

This method invokes the implFlush method to perform the actual flushing operation.

Parameters:
out The output character buffer
Returns:
A coder-result object, either CoderResult#UNDERFLOW or CoderResult#OVERFLOW
Exceptions:
IllegalStateException If the previous step of the current decoding operation was an invocation neither of the reset method nor of the three-argument decode method with a value of true for the endOfInput parameter

Ref<CoderResult> java::io::CharsetDecoder::decode ( Array< jbyte > &  in,
Array< jchar > &  out,
jboolean  endOfInput 
)

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:

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 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
Exceptions:
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

Array<jchar> java::io::CharsetDecoder::decode ( Array< jbyte > &  in  ) 

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.
Exceptions:
IllegalStateException If a decoding operation is already in progress
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
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 CodingErrorAction#REPORT

virtual Ref<CoderResult> java::io::CharsetDecoder::implFlush ( Array< jchar > &  out  )  [protected, virtual]

Flushes this coder.

The default implementation of this method does nothing, and always returns CoderResult#UNDERFLOW. This method should be overridden by coders 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 CoderResult#UNDERFLOW or CoderResult#OVERFLOW

virtual Ref<CoderResult> java::io::CharsetDecoder::decodeLoop ( Array< jbyte > &  in,
Array< jchar > &  out 
) [protected, pure virtual]

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


The documentation for this class was generated from the following file:
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