org.codehaus.stax2.ri.typed

Class AsciiValueEncoder

java.lang.Object

org.codehaus.stax2.ri.typed.AsciiValueEncoder

public abstract class AsciiValueEncoder
extends Object

This base class defines interface used for efficient encoding of typed values, by stream writers. The abstraction is necessary to reduce amount of duplicated code while avoiding significant additional overhead. The idea is that the low-level stream writer backend supplies encoder with the result buffer, while encoder itself knows the data and state. Together these allow for efficient serialization with light coupling.

General contract for encoding is that caller must call things in following sequence:

1. First, bufferNeedsFlush(int) is called once; and if indicated by return value of true, caller must flush its buffer so it is completely empty (buffer also must have size of at at least MIN_CHARS_WITHOUT_FLUSH)
2. Then, one of encodeMore(char[], int, int) methods is to be called
3. After this call, isCompleted() should be called to determine if encoding was complete: if it was, there is nothing more to do.
4. Otherwise caller should flush its buffer (since encoder has encoded as much as it can without flushing), and repeat cycle of calls to encodeMore(char[], int, int) followed by a call to isCompleted() and flushing, as long as necessary to complete encoding.

Main restrictions for use are that value serializations must produce only 7-bit ascii characters, and that the value can be produced incrementally using limited size buffers. This is true for all current value types of the Typed Access API.

Finally, details of how encoders are created and/or reused is outside scope of this public interface. Stax2 reference implementation handles this using an encoder factory that knows construction details.

Since:

3.0

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	MIN_CHARS_WITHOUT_FLUSH Constant used to determine when caller should flush buffer before calling encode methods.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AsciiValueEncoder()

Method Summary

Methods

Modifier and Type	Method and Description
boolean	bufferNeedsFlush(int freeChars) Method called by writer to check if it should flush its output buffer (which has specified amount of free space) before encoder can encode more data.
abstract int	encodeMore(byte[] buffer, int ptr, int end)
abstract int	encodeMore(char[] buffer, int ptr, int end)
abstract boolean	isCompleted() Method that can alternatively be called to determine whether encoder has encoded all data it has.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MIN_CHARS_WITHOUT_FLUSH

protected static final int MIN_CHARS_WITHOUT_FLUSH

Constant used to determine when caller should flush buffer before calling encode methods. Strict minimum would be something like 22 (for floating point numbers), but let's pad it a bit.

See Also:

Constant Field Values

Constructor Detail

AsciiValueEncoder

protected AsciiValueEncoder()

Method Detail

bufferNeedsFlush

public final boolean bufferNeedsFlush(int freeChars)

Method called by writer to check if it should flush its output buffer (which has specified amount of free space) before encoder can encode more data. Flushing is only needed if (a) encoder has more data to output, and (b) free space is not enough to contain smallest segment of encoded value (individual array element or encoded primitive value).

Parameters:

freeChars - Amount of free space (in characters) in the output buffer

Returns:

True if encoder still has data to output and specified amount of free space is insufficient for encoding any more data

isCompleted

public abstract boolean isCompleted()

Method that can alternatively be called to determine whether encoder has encoded all data it has. Generally called right after a call to encodeMore(char[], int, int), to figure out whether buffer flush is needed (there is more data), or encoding is complete.

encodeMore

public abstract int encodeMore(char[] buffer,
             int ptr,
             int end)

Returns:

Value of pointer after all remaining data (which may be "none") that can be encoded (as constrained by buffer length) has been encoded. Has to exceed 'ptr' value sent in; will be equal to it if nothing was encoded (which should only occur when everything has been encoded, as long as bufferNeedsFlush(int) is appropriately called once before calling this method)

encodeMore

public abstract int encodeMore(byte[] buffer,
             int ptr,
             int end)

Returns:

Value of pointer after all remaining data (which may be "none") that can be encoded (as constrained by buffer length) has been encoded. Has to exceed 'ptr' value sent in; will be equal to it if nothing was encoded (which should only occur when everything has been encoded, as long as bufferNeedsFlush(int) is appropriately called once before calling this method)