net.sf.saxon.regex

Class REMatcher

java.lang.Object

net.sf.saxon.regex.REMatcher

public class REMatcher
extends java.lang.Object

RE is an efficient, lightweight regular expression evaluator/matcher class. Regular expressions are pattern descriptions which enable sophisticated matching of strings. In addition to being able to match a string against a pattern, you can also extract parts of the match. This is especially useful in text parsing! Details on the syntax of regular expression patterns are given below.

To compile a regular expression (RE), you can simply construct an RE matcher object from the string specification of the pattern, like this:

  RE r = new RE("a*b");
 

Once you have done this, you can call either of the RE.match methods to perform matching on a String. For example:

  boolean matched = r.match("aaaab");
 

will cause the boolean matched to be set to true because the pattern "a*b" matches the string "aaaab".

If you were interested in the number of a's which matched the first part of our example expression, you could change the expression to "(a*)b". Then when you compiled the expression and matched it against something like "xaaaab", you would get results like this:

  RE r = new RE("(a*)b");                  // Compile expression
  boolean matched = r.match("xaaaab");     // Match against "xaaaab"

  String wholeExpr = r.getParen(0);        // wholeExpr will be 'aaaab'
  String insideParens = r.getParen(1);     // insideParens will be 'aaaa'

  int startWholeExpr = r.getParenStart(0); // startWholeExpr will be index 1
  int endWholeExpr = r.getParenEnd(0);     // endWholeExpr will be index 6
  int lenWholeExpr = r.getParenLength(0);  // lenWholeExpr will be 5

  int startInside = r.getParenStart(1);    // startInside will be index 1
  int endInside = r.getParenEnd(1);        // endInside will be index 5
  int lenInside = r.getParenLength(1);     // lenInside will be 4
 

You can also refer to the contents of a parenthesized expression within a regular expression itself. This is called a 'backreference'. The first backreference in a regular expression is denoted by \1, the second by \2 and so on. So the expression:

  ([0-9]+)=\1
 

will match any string of the form n=n (like 0=0 or 2=2).

The full regular expression syntax accepted by RE is as defined in the XSD 1.1 specification, modified by the XPath 2.0 or 3.0 specifications.

Line terminators

A line terminator is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators:

• A newline (line feed) character ('\n'),
• A carriage-return character followed immediately by a newline character ("\r\n"),
• A standalone carriage-return character ('\r'),
• A next-line character ('…'),
• A line-separator character ('
'), or
• A paragraph-separator character ('
).

RE runs programs compiled by the RECompiler class. But the RE matcher class does not include the actual regular expression compiler for reasons of efficiency. In fact, if you want to pre-compile one or more regular expressions, the 'recompile' class can be invoked from the command line to produce compiled output like this:

    // Pre-compiled regular expression "a*b"
    char[] re1Instructions =
    {
        0x007c, 0x0000, 0x001a, 0x007c, 0x0000, 0x000d, 0x0041,
        0x0001, 0x0004, 0x0061, 0x007c, 0x0000, 0x0003, 0x0047,
        0x0000, 0xfff6, 0x007c, 0x0000, 0x0003, 0x004e, 0x0000,
        0x0003, 0x0041, 0x0001, 0x0004, 0x0062, 0x0045, 0x0000,
        0x0000,
    };


    REProgram re1 = new REProgram(re1Instructions);
 

You can then construct a regular expression matcher (RE) object from the pre-compiled expression re1 and thus avoid the overhead of compiling the expression at runtime. If you require more dynamic regular expressions, you can construct a single RECompiler object and re-use it to compile each expression. Similarly, you can change the program run by a given matcher object at any time. However, RE and RECompiler are not threadsafe (for efficiency reasons, and because requiring thread safety in this class is deemed to be a rare requirement), so you will need to construct a separate compiler or matcher object for each thread (unless you do thread synchronization yourself). Once expression compiled into the REProgram object, REProgram can be safely shared across multiple threads and RE objects.

ISSUES:

• Not *all* possibilities are considered for greediness when backreferences are involved (as POSIX suggests should be the case). The POSIX RE "(ac*)c*d[ac]*\1", when matched against "acdacaa" should yield a match of acdacaa where \1 is "a". This is not the case in this RE package, and actually Perl doesn't go to this extent either! Until someone actually complains about this, I'm not sure it's worth "fixing". If it ever is fixed, test #137 in RETest.txt should be updated.

This library is based on the Apache Jakarta regex library as downloaded on 3 January 2012. Changes have been made to make the grammar and semantics conform to XSD and XPath rules; these changes are listed in source code comments in the RECompiler source code module.

Author:

Jonathan Locke, Tobias Schäfer, Michael Kay

See Also:

RECompiler

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	REMatcher.State

Constructor Summary

Constructors

Constructor and Description
REMatcher(REProgram program) Construct a matcher for a pre-compiled regular expression from program (bytecode) data.

Method Summary

Modifier and Type	Method and Description
boolean	anchoredMatch(UnicodeString search) Tests whether the regex matches a string in its entirety, anchored at both ends
REMatcher.State	captureState()
protected void	clearCapturedGroupsBeyond(int pos) Clear any captured groups whose start position is at or beyond some specified position
UnicodeString	getParen(int which) Gets the contents of a parenthesized subexpression after a successful match.
int	getParenCount() Returns the number of parenthesized subexpressions available after a successful match.
int	getParenEnd(int which) Returns the end index of a given paren level.
int	getParenStart(int which) Returns the start index of a given paren level.
REProgram	getProgram() Returns the current regular expression program in use by this matcher object.
boolean	match(java.lang.String search) Matches the current regular expression program against a String.
boolean	match(UnicodeString search, int i) Matches the current regular expression program against a character array, starting at a given index.
protected boolean	matchAt(int i, boolean anchored) Match the current regular expression program against the current input string, starting at index i of the input string.
java.lang.CharSequence	replace(UnicodeString in, UnicodeString replacement) Substitutes a string for this regular expression in another string.
void	resetState(REMatcher.State state)
protected void	setParenEnd(int which, int i) Sets the end of a paren level
protected void	setParenStart(int which, int i) Sets the start of a paren level
void	setProgram(REProgram program) Sets the current regular expression program used by this matcher object.
java.util.List<UnicodeString>	split(UnicodeString s) Splits a string into an array of strings on regular expression boundaries.

Methods inherited from class java.lang.Object

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

Constructor Detail

REMatcher

public REMatcher(REProgram program)

Construct a matcher for a pre-compiled regular expression from program (bytecode) data.

Parameters:

program - Compiled regular expression program

See Also:

RECompiler

Method Detail

setProgram

public void setProgram(REProgram program)

Sets the current regular expression program used by this matcher object.

Parameters:

program - Regular expression program compiled by RECompiler.

See Also:

RECompiler, REProgram

getProgram

public REProgram getProgram()

Returns the current regular expression program in use by this matcher object.

Returns:

Regular expression program

See Also:

setProgram(net.sf.saxon.regex.REProgram)

getParenCount

public int getParenCount()

Returns the number of parenthesized subexpressions available after a successful match.

Returns:

Number of available parenthesized subexpressions

getParen

public UnicodeString getParen(int which)

Gets the contents of a parenthesized subexpression after a successful match.

Parameters:

which - Nesting level of subexpression

Returns:

String

getParenStart

public final int getParenStart(int which)

Returns the start index of a given paren level.

Parameters:

which - Nesting level of subexpression

Returns:

String index

getParenEnd

public final int getParenEnd(int which)

Returns the end index of a given paren level.

Parameters:

which - Nesting level of subexpression

Returns:

String index

setParenStart

protected final void setParenStart(int which,
                                   int i)

Sets the start of a paren level

Parameters:

which - Which paren level

i - Index in input array

setParenEnd

protected final void setParenEnd(int which,
                                 int i)

Sets the end of a paren level

Parameters:

which - Which paren level

i - Index in input array

clearCapturedGroupsBeyond

protected void clearCapturedGroupsBeyond(int pos)

Clear any captured groups whose start position is at or beyond some specified position

Parameters:

pos - the specified position

matchAt

protected boolean matchAt(int i,
                          boolean anchored)

Match the current regular expression program against the current input string, starting at index i of the input string. This method is only meant for internal use.

Parameters:

i - The input string index to start matching at

anchored - true if the regex must match all characters up to the end of the string

Returns:

True if the input matched the expression

anchoredMatch

public boolean anchoredMatch(UnicodeString search)

Tests whether the regex matches a string in its entirety, anchored at both ends

Parameters:

search - the string to be matched

Returns:

true if the regex matches the whols string

match

public boolean match(UnicodeString search,
                     int i)

Matches the current regular expression program against a character array, starting at a given index.

Parameters:

search - String to match against

i - Index to start searching at

Returns:

True if string matched

match

public boolean match(java.lang.String search)

Matches the current regular expression program against a String.

Parameters:

search - String to match against

Returns:

True if string matched

split

public java.util.List<UnicodeString> split(UnicodeString s)

Splits a string into an array of strings on regular expression boundaries. This function works the same way as the Perl function of the same name. Given a regular expression of "[ab]+" and a string to split of "xyzzyababbayyzabbbab123", the result would be the array of Strings "[xyzzy, yyz, 123]".

Please note that the first string in the resulting array may be an empty string. This happens when the very first character of input string is matched by the pattern.

Parameters:

s - String to split on this regular exression

Returns:

Array of strings

replace

public java.lang.CharSequence replace(UnicodeString in,
                                      UnicodeString replacement)

Substitutes a string for this regular expression in another string. This method works like the Perl function of the same name. Given a regular expression of "a*b", a String to substituteIn of "aaaabfooaaabgarplyaaabwackyb" and the substitution String "-", the resulting String returned by subst would be "-foo-garply-wacky-".

It is also possible to reference the contents of a parenthesized expression with $0, $1, ... $9. A regular expression of "http://[\\.\\w\\-\\?/~_@&=%]+", a String to substituteIn of "visit us: http://www.apache.org!" and the substitution String "<a href=\"$0\">$0</a>", the resulting String returned by subst would be "visit us: <a href=\"http://www.apache.org\">http://www.apache.org</a>!".

Note: $0 represents the whole match.

Parameters:

in - String to substitute within

replacement - String to substitute for matches of this regular expression

Returns:

The string substituteIn with zero or more occurrences of the current regular expression replaced with the substitution String (if this regular expression object doesn't match at any position, the original String is returned unchanged).

captureState

public REMatcher.State captureState()

resetState

public void resetState(REMatcher.State state)