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org.apache.regexp
Class RE

java.lang.Object
  |
  +--org.apache.regexp.RE
public class RE
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 = getParenStart(0);   // startWholeExpr will be index 1
     int endWholeExpr = getParenEnd(0);       // endWholeExpr will be index 6
     int lenWholeExpr = getParenLength(0);    // lenWholeExpr will be 5

 


     int startInside = getParenStart(1);      // startInside will be index 1
     int endInside = getParenEnd(1);          // endInside will be index 5
     int lenInside = 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 described here: 


 


  Characters

 


    unicodeChar          Matches any identical unicode character
    \                    Used to quote a meta-character (like '*')
    \\                   Matches a single '\' character
    \0nnn                Matches a given octal character
    \xhh                 Matches a given 8-bit hexadecimal character
    \\uhhhh               Matches a given 16-bit hexadecimal character
    \t                   Matches an ASCII tab character
    \n                   Matches an ASCII newline character
    \r                   Matches an ASCII return character
    \f                   Matches an ASCII form feed character

 


  Character Classes

 


    [abc]                Simple character class
    [a-zA-Z]             Character class with ranges
    [^abc]               Negated character class

 


  Standard POSIX Character Classes

 


    [:alnum:]            Alphanumeric characters. 
    [:alpha:]            Alphabetic characters. 
    [:blank:]            Space and tab characters. 
    [:cntrl:]            Control characters. 
    [:digit:]            Numeric characters. 
    [:graph:]            Characters that are printable and are also visible. (A space is printable, but not visible, while an `a' is both.) 
    [:lower:]            Lower-case alphabetic characters. 
    [:print:]            Printable characters (characters that are not control characters.) 
    [:punct:]            Punctuation characters (characters that are not letter, digits, control characters, or space characters). 
    [:space:]            Space characters (such as space, tab, and formfeed, to name a few). 
    [:upper:]            Upper-case alphabetic characters. 
    [:xdigit:]           Characters that are hexadecimal digits.
         
 


  Non-standard POSIX-style Character Classes

 


    [:javastart:]        Start of a Java identifier
    [:javapart:]         Part of a Java identifier

 

         
  Predefined Classes

 


    .                    Matches any character other than newline
    \w                   Matches a "word" character (alphanumeric plus "_")
    \W                   Matches a non-word character
    \s                   Matches a whitespace character
    \S                   Matches a non-whitespace character
    \d                   Matches a digit character
    \D                   Matches a non-digit character

 


  Boundary Matchers

 


    ^                    Matches only at the beginning of a line
    $                    Matches only at the end of a line
    \b                   Matches only at a word boundary
    \B                   Matches only at a non-word boundary

 


  Greedy Closures

 


    A*                   Matches A 0 or more times (greedy)
    A+                   Matches A 1 or more times (greedy)
    A?                   Matches A 1 or 0 times (greedy)
    A{n}                 Matches A exactly n times (greedy)
    A{n,}                Matches A at least n times (greedy)
    A{n,m}               Matches A at least n but not more than m times (greedy)

 


  Reluctant Closures

 


    A*?                  Matches A 0 or more times (reluctant)
    A+?                  Matches A 1 or more times (reluctant)
    A??                  Matches A 0 or 1 times (reluctant)

 


  Logical Operators

 


    AB                   Matches A followed by B
    A|B                  Matches either A or B
    (A)                  Used for subexpression grouping

 


  Backreferences

 


    \1                   Backreference to 1st parenthesized subexpression
    \2                   Backreference to 2nd parenthesized subexpression
    \3                   Backreference to 3rd parenthesized subexpression
    \4                   Backreference to 4th parenthesized subexpression
    \5                   Backreference to 5th parenthesized subexpression
    \6                   Backreference to 6th parenthesized subexpression
    \7                   Backreference to 7th parenthesized subexpression
    \8                   Backreference to 8th parenthesized subexpression
    \9                   Backreference to 9th parenthesized subexpression

All closure operators (+, *, ?, {m,n}) are greedy by default, meaning that they match as many elements of the string as possible without causing the overall match to fail. If you want a closure to be reluctant (non-greedy), you can simply follow it with a '?'. A reluctant closure will match as few elements of the string as possible when finding matches. {m,n} closures don't currently support reluctancy.

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).


ISSUES:

See Also:
recompile, RECompiler

Field Summary
static int MATCH_CASEINDEPENDENT
          Flag to indicate that matching should be case-independent (folded)
static int MATCH_MULTILINE
          Newlines should match as BOL/EOL (^ and $)
static int MATCH_NORMAL
          Specifies normal, case-sensitive matching behaviour.
static int MATCH_SINGLELINE
          Consider all input a single body of text - newlines are matched by .
static int REPLACE_ALL
          Flag bit that indicates that subst should replace all occurrences of this regular expression.
static int REPLACE_FIRSTONLY
          Flag bit that indicates that subst should only replace the first occurrence of this regular expression.
 
Constructor Summary
RE()
          Constructs a regular expression matcher with no initial program.
RE(REProgram program)
          Construct a matcher for a pre-compiled regular expression from program (bytecode) data.
RE(REProgram program, int matchFlags)
          Construct a matcher for a pre-compiled regular expression from program (bytecode) data.
RE(java.lang.String pattern)
          Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler.
RE(java.lang.String pattern, int matchFlags)
          Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler.
 
Method Summary
 int getMatchFlags()
          Returns the current match behaviour flags.
 java.lang.String 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 getParenLength(int which)
          Returns the length 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.
 java.lang.String[] grep(java.lang.Object[] search)
          Returns an array of Strings, whose toString representation matches a regular expression.
protected  void internalError(java.lang.String s)
          Throws an Error representing an internal error condition probably resulting from a bug in the regular expression compiler (or possibly data corruption).
 boolean match(CharacterIterator search, int i)
          Matches the current regular expression program against a character array, starting at a given index.
 boolean match(java.lang.String search)
          Matches the current regular expression program against a String.
 boolean match(java.lang.String search, int i)
          Matches the current regular expression program against a character array, starting at a given index.
protected  boolean matchAt(int i)
          Match the current regular expression program against the current input string, starting at index i of the input string.
protected  int matchNodes(int firstNode, int lastNode, int idxStart)
          Try to match a string against a subset of nodes in the program
 void setMatchFlags(int matchFlags)
          Sets match behaviour flags which alter the way RE does matching.
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.
static java.lang.String simplePatternToFullRegularExpression(java.lang.String pattern)
          Converts a 'simplified' regular expression to a full regular expression
 java.lang.String[] split(java.lang.String s)
          Splits a string into an array of strings on regular expression boundaries.
 java.lang.String subst(java.lang.String substituteIn, java.lang.String substitution)
          Substitutes a string for this regular expression in another string.
 java.lang.String subst(java.lang.String substituteIn, java.lang.String substitution, int flags)
          Substitutes a string for this regular expression in another string.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

MATCH_NORMAL

public static final int MATCH_NORMAL
Specifies normal, case-sensitive matching behaviour.

MATCH_CASEINDEPENDENT

public static final int MATCH_CASEINDEPENDENT
Flag to indicate that matching should be case-independent (folded)

MATCH_MULTILINE

public static final int MATCH_MULTILINE
Newlines should match as BOL/EOL (^ and $)

MATCH_SINGLELINE

public static final int MATCH_SINGLELINE
Consider all input a single body of text - newlines are matched by .

REPLACE_ALL

public static final int REPLACE_ALL
Flag bit that indicates that subst should replace all occurrences of this regular expression.

REPLACE_FIRSTONLY

public static final int REPLACE_FIRSTONLY
Flag bit that indicates that subst should only replace the first occurrence of this regular expression.

Constructor Detail

RE

public RE(java.lang.String pattern)
   throws RESyntaxException
Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler. If you will be compiling many expressions, you may prefer to use a single RECompiler object instead.

Parameters:
pattern - The regular expression pattern to compile.
Throws:
RESyntaxException - Thrown if the regular expression has invalid syntax.
See Also:
RECompiler, recompile

RE

public RE(java.lang.String pattern,
          int matchFlags)
   throws RESyntaxException
Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler. If you will be compiling many expressions, you may prefer to use a single RECompiler object instead.

Parameters:
pattern - The regular expression pattern to compile.
matchFlags - The matching style
Throws:
RESyntaxException - Thrown if the regular expression has invalid syntax.
See Also:
RECompiler, recompile

RE

public RE(REProgram program,
          int matchFlags)
Construct a matcher for a pre-compiled regular expression from program (bytecode) data. Permits special flags to be passed in to modify matching behaviour.

Parameters:
program - Compiled regular expression program (see RECompiler and/or recompile)
matchFlags - One or more of the RE match behaviour flags (RE.MATCH_*): 

   MATCH_NORMAL              // Normal (case-sensitive) matching
   MATCH_CASEINDEPENDENT     // Case folded comparisons
   MATCH_MULTILINE           // Newline matches as BOL/EOL
See Also:
RECompiler, REProgram, recompile

RE

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

Parameters:
program - Compiled regular expression program
See Also:
RECompiler, recompile

RE

public RE()
Constructs a regular expression matcher with no initial program. This is likely to be an uncommon practice, but is still supported.

Method Detail

simplePatternToFullRegularExpression

public static java.lang.String simplePatternToFullRegularExpression(java.lang.String pattern)
Converts a 'simplified' regular expression to a full regular expression

Parameters:
pattern - The pattern to convert
Returns:
The full regular expression

setMatchFlags

public void setMatchFlags(int matchFlags)
Sets match behaviour flags which alter the way RE does matching.

Parameters:
matchFlags - One or more of the RE match behaviour flags (RE.MATCH_*): 

   MATCH_NORMAL              // Normal (case-sensitive) matching
   MATCH_CASEINDEPENDENT     // Case folded comparisons
   MATCH_MULTILINE           // Newline matches as BOL/EOL

getMatchFlags

public int getMatchFlags()
Returns the current match behaviour flags.

Returns:
Current match behaviour flags (RE.MATCH_*). 

   MATCH_NORMAL              // Normal (case-sensitive) matching
   MATCH_CASEINDEPENDENT     // Case folded comparisons
   MATCH_MULTILINE           // Newline matches as BOL/EOL
See Also:
setMatchFlags(int)

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, recompile

getProgram

public REProgram getProgram()
Returns the current regular expression program in use by this matcher object.

Returns:
Regular expression program
See Also:
setProgram(org.apache.regexp.REProgram)

getParenCount

public int getParenCount()
Returns the number of parenthesized subexpressions available after a successful match.

Returns:
Number of available parenthesized subexpressions

getParen

public java.lang.String 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

getParenLength

public final int getParenLength(int which)
Returns the length of a given paren level.

Parameters:
which - Nesting level of subexpression
Returns:
Number of characters in the parenthesized subexpression

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

internalError

protected void internalError(java.lang.String s)
                      throws java.lang.Error
Throws an Error representing an internal error condition probably resulting from a bug in the regular expression compiler (or possibly data corruption). In practice, this should be very rare.

Parameters:
s - Error description

matchNodes

protected int matchNodes(int firstNode,
                         int lastNode,
                         int idxStart)
Try to match a string against a subset of nodes in the program

Parameters:
firstNode - Node to start at in program
lastNode - Last valid node (used for matching a subexpression without matching the rest of the program as well).
idxStart - Starting position in character array
Returns:
Final input array index if match succeeded. -1 if not.

matchAt

protected boolean matchAt(int i)
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
Returns:
True if the input matched the expression

match

public boolean match(java.lang.String 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(CharacterIterator 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.lang.String[] split(java.lang.String 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]".

Parameters:
s - String to split on this regular exression
Returns:
Array of strings

subst

public java.lang.String subst(java.lang.String substituteIn,
                              java.lang.String substitution)
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-".

Parameters:
substituteIn - String to substitute within
substitution - String to substitute for all 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).

subst

public java.lang.String subst(java.lang.String substituteIn,
                              java.lang.String substitution,
                              int flags)
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-".

Parameters:
substituteIn - String to substitute within
substitution - String to substitute for matches of this regular expression
flags - One or more bitwise flags from REPLACE_*. If the REPLACE_FIRSTONLY flag bit is set, only the first occurrence of this regular expression is replaced. If the bit is not set (REPLACE_ALL), all occurrences of this pattern will be replaced.
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).

grep

public java.lang.String[] grep(java.lang.Object[] search)
Returns an array of Strings, whose toString representation matches a regular expression. This method works like the Perl function of the same name. Given a regular expression of "a*b" and an array of String objects of [foo, aab, zzz, aaaab], the array of Strings returned by grep would be [aab, aaaab].

Parameters:
search - Array of Objects to search
Returns:
Array of Objects whose toString value matches this regular expression.
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