net.loomchild.segment.srx

Class SrxTextIterator

java.lang.Object

net.loomchild.segment.AbstractTextIterator

net.loomchild.segment.srx.SrxTextIterator

All Implemented Interfaces:

Iterator<String>, TextIterator

public class SrxTextIterator
extends AbstractTextIterator

Represents text iterator splitting text according to rules in SRX file. The algorithm idea is as follows:

 1. Rule matcher list is created based on SRX file and language. Each rule 
    matcher is responsible for matching before break and after break regular 
    expressions of one break rule.
 2. Each rule matcher is matched to the text. If the rule was not found the 
    rule matcher is removed from the list. 
 3. First rule matcher in terms of its break position in text is selected.
 4. List of exception rules corresponding to break rule is retrieved. 
 5. If none of exception rules is matching in break position then 
    the text is marked as split and new segment is created. In addition 
    all rule matchers are moved so they start after the end of new segment 
    (which is the same as break position of the matched rule). 
 6. All the rules that have break position behind last matched rule 
    break position are moved until they pass it.
 7. If segment was not found the whole process is repeated.
 

In streaming version of this algorithm character buffer is searched. When the end of it is reached or break position is in the margin (break position > buffer size - margin) and there is more text, the buffer is moved in the text until it starts after last found segment. If this happens rule matchers are reinitialized and the text is searched again. Streaming version has a limitation that read buffer must be at least as long as any segment in the text. As this algorithm uses lookbehind extensively but Java does not permit infinite regular expressions in lookbehind, so some patterns are finitized. For example a* pattern will be changed to something like a{0,100}.

Author:

loomchild

Field Summary

Fields

Modifier and Type	Field and Description
static String	BUFFER_LENGTH_PARAMETER Reader buffer size.
static int	DEFAULT_BUFFER_LENGTH Default size of read buffer when using streaming version of this class.
static int	DEFAULT_MARGIN Default margin size.
static int	DEFAULT_MAX_LOOKBEHIND_CONSTRUCT_LENGTH Default max lookbehind construct length parameter.
static String	MARGIN_PARAMETER Margin size.
static String	MAX_LOOKBEHIND_CONSTRUCT_LENGTH_PARAMETER Maximum length of a regular expression construct that occurs in lookbehind.

Constructor Summary

Constructors

Constructor and Description
SrxTextIterator(SrxDocument document, String languageCode, CharSequence text) Creates text iterator with no additional parameters.
SrxTextIterator(SrxDocument document, String languageCode, CharSequence text, Map<String,Object> parameterMap) Creates text iterator that obtains language rules form given document using given language code.
SrxTextIterator(SrxDocument document, String languageCode, Reader reader) Creates streaming text iterator with no additional parameters.
SrxTextIterator(SrxDocument document, String languageCode, Reader reader, Map<String,Object> parameterMap) Creates text iterator that obtains language rules from given document using given language code.

Method Summary

Modifier and Type	Method and Description
boolean	hasNext()
String	next() Finds the next segment in the text and returns it.

Methods inherited from class net.loomchild.segment.AbstractTextIterator

remove, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

forEachRemaining

Field Detail

MARGIN_PARAMETER

public static final String MARGIN_PARAMETER

Margin size. Used in streaming splitter. If rule is matched but its position is in the margin (position > bufferLength - margin) then the matching is ignored, and more text is read and rule is matched again.

See Also:

Constant Field Values

BUFFER_LENGTH_PARAMETER

public static final String BUFFER_LENGTH_PARAMETER

Reader buffer size. Segments cannot be longer than this value.

See Also:

Constant Field Values

MAX_LOOKBEHIND_CONSTRUCT_LENGTH_PARAMETER

public static final String MAX_LOOKBEHIND_CONSTRUCT_LENGTH_PARAMETER

Maximum length of a regular expression construct that occurs in lookbehind.

See Also:

Constant Field Values

DEFAULT_MARGIN

public static final int DEFAULT_MARGIN

Default margin size.

See Also:

Constant Field Values

DEFAULT_BUFFER_LENGTH

public static final int DEFAULT_BUFFER_LENGTH

Default size of read buffer when using streaming version of this class. Any segment cannot be longer than buffer size.

See Also:

Constant Field Values

DEFAULT_MAX_LOOKBEHIND_CONSTRUCT_LENGTH

public static final int DEFAULT_MAX_LOOKBEHIND_CONSTRUCT_LENGTH

Default max lookbehind construct length parameter.

See Also:

Constant Field Values

Constructor Detail

SrxTextIterator

public SrxTextIterator(SrxDocument document,
                       String languageCode,
                       CharSequence text,
                       Map<String,Object> parameterMap)

Creates text iterator that obtains language rules form given document using given language code. This constructor version is not streaming because it receives whole text as a string. Supported parameters: MAX_LOOKBEHIND_CONSTRUCT_LENGTH_PARAMETER.

Parameters:

document - SRX document

languageCode - text language code of text used to retrieve the rules

text -

parameterMap - additional segmentation parameters

SrxTextIterator

public SrxTextIterator(SrxDocument document,
                       String languageCode,
                       CharSequence text)

Creates text iterator with no additional parameters.

Parameters:

document - SRX document

languageCode - text language code of text used to retrieve the rules

text -

See Also:

SrxTextIterator(SrxDocument, String, CharSequence, Map)

SrxTextIterator

public SrxTextIterator(SrxDocument document,
                       String languageCode,
                       Reader reader,
                       Map<String,Object> parameterMap)

Creates text iterator that obtains language rules from given document using given language code. This is streaming constructor - it reads text from reader using buffer with given size and margin. Single segment cannot be longer than buffer size. If rule is matched but its position is in the margin (position > bufferLength - margin) then the matching is ignored, and more text is read and rule is matched again. This is needed because incomplete rule can be located at the end of the buffer and never matched. Supported parameters: BUFFER_LENGTH_PARAMETER, MARGIN_PARAMETER, MAX_LOOKBEHIND_CONSTRUCT_LENGTH_PARAMETER.

Parameters:

document - SRX document

languageCode - text language code of text used to retrieve the rules

reader - reader from which read the text

parameterMap - additional segmentation parameters

SrxTextIterator

public SrxTextIterator(SrxDocument document,
                       String languageCode,
                       Reader reader)

Creates streaming text iterator with no additional parameters.

Parameters:

document - SRX document

languageCode - text language code of text used to retrieve the rules

reader - reader from which read the text

See Also:

SrxTextIterator(SrxDocument, String, Reader, Map)

Method Detail

next

public String next()

Finds the next segment in the text and returns it.

Returns:

next segment or null if it doesn't exist

Throws:

IllegalStateException - if buffer is too small to hold the segment

IORuntimeException - if IO error occurs when reading the text

hasNext

public boolean hasNext()

Returns:

true if there are more segments