java::io::CharsetEncoder Class Reference

Inheritance diagram for java::io::CharsetEncoder:

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

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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 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:

  1. Reset the encoder via the reset method, unless it has not been used before;

  2. 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;

  3. Invoke the encode method one final time, passing true for the endOfInput argument; and then

  4. Invoke the flush method so that the encoder can flush any internal state to the output buffer.

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.

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.

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

JSR-51 Expert Group

Since:
1.4
See also:
ByteBuffer

CharBuffer

Charset

CharsetDecoder


Public Member Functions

jboolean isLegalReplacement (const String &repl) const
 Tells whether or not the given byte array is a legal replacement value for this encoder.
Ref< CoderResultflush (Array< jbyte > &out)
 Flushes this encoder.
Ref< CoderResultencode (Array< jchar > &in, Array< jbyte > &out, jboolean endOfInput)
 Encodes as many characters as possible from the given input buffer, writing the results to the given output buffer.
Array< jbyteencode (Array< jchar > &in)
 Convenience method that encodes the remaining content of a single input character buffer into a newly-allocated byte buffer.
jboolean canEncode (const Array< jchar > &in)
 Tells whether or not this encoder can encode the given character sequence.

Protected Member Functions

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

Constructor & Destructor Documentation

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

Initializes a new encoder.

The new encoder will have the given bytes-per-char and replacement values.

Parameters:
averageRatio A positive float value indicating the expected number of bytes that will be produced for each input character
maxRatio A positive float value indicating the maximum number of bytes that will be produced for each input character
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

jboolean java::io::CharsetEncoder::isLegalReplacement ( const String repl  )  const

Tells whether or not the given byte array is a legal replacement value for this encoder.

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.

Parameters:
repl The byte array to be tested
Returns:
true if, and only if, the given byte array is a legal replacement value for this encoder

Ref<CoderResult> java::io::CharsetEncoder::flush ( Array< jbyte > &  out  ) 

Flushes this encoder.

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.

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

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

Encodes as many characters 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() 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:

In any case, if this method is to be reinvoked in the same encoding operation then care should be taken to preserve any characters 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 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.

Parameters:
in The input character buffer
out The output byte buffer
endOfInput true if, and only if, the invoker can provide no additional input characters beyond those in the given buffer
Returns:
A coder-result object describing the reason for termination
Exceptions:
IllegalStateException If a encoding 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 encoding operation
CoderMalfunctionError If an invocation of the encodeLoop method threw an unexpected exception

Array<jbyte> java::io::CharsetEncoder::encode ( Array< jchar > &  in  ) 

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

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 a encoding operation is already in progress.

Parameters:
in The input character buffer
Returns:
A newly-allocated byte buffer containing the result of the encoding operation. The buffer's position will be zero and its limit will follow the last byte written.
Exceptions:
IllegalStateException If an encoding operation is already in progress
MalformedInputException If the character sequence starting at the input buffer's current position is not a legal sixteen-bit Unicode sequence and the current malformed-input action is CodingErrorAction#REPORT
UnmappableCharacterException If the character sequence starting at the input buffer's current position cannot be mapped to an equivalent byte sequence and the current unmappable-character action is CodingErrorAction#REPORT

jboolean java::io::CharsetEncoder::canEncode ( const Array< jchar > &  in  ) 

Tells whether or not this encoder can encode the given character sequence.

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.

Returns:
true if, and only if, this encoder can encode the given character without throwing any exceptions and without performing any replacements
Exceptions:
IllegalStateException If an encoding operation is already in progress

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

Flushes this encoder.

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.

Parameters:
out The output byte buffer
Returns:
A coder-result object, either CoderResult#UNDERFLOW or CoderResult#OVERFLOW

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

Encodes one or more characters into one or more bytes.

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 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.

Parameters:
in The input character buffer
out The output byte 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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