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 :
Reset the encoder via the
reset method, unless it has not been used before;
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;
encode method one final time, passing
true for the
endOfInput argument; and then
flush method so that the encoder can flush any internal state to the output buffer.
Each invocation of the
method will encode as many characters as possible from the input buffer, writing the resulting bytes to the output buffer. The
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
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
}; its value may be changed via the
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
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
Instances of this class are not safe for use by multiple concurrent threads.