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Jakarta-ORO 2.0.6 API: Class Perl5Util
Jakarta ORO

org.apache.oro.text.perl
Class Perl5Util

java.lang.Object
  |
  +--org.apache.oro.text.perl.Perl5Util
All Implemented Interfaces:
MatchResult

public final class Perl5Util
extends java.lang.Object
implements MatchResult

This is a utility class implementing the 3 most common Perl5 operations involving regular expressions:

  • [m]/pattern/[i][m][s][x],
  • s/pattern/replacement/[g][i][m][o][s][x],
  • and split().
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

The objective of the class is to minimize the amount of code a Java programmer using Jakarta-ORO has to write to achieve the same results as Perl by transparently handling regular expression compilation, caching, and matching. A second objective is to use the same Perl pattern matching syntax to ease the task of Perl programmers transitioning to Java (this also reduces the number of parameters to a method). All the state affecting methods are synchronized to avoid the maintenance of explicit locks in multithreaded programs. This philosophy differs from the org.apache.oro.text.regex package, where you are expected to either maintain explicit locks, or more preferably create separate compiler and matcher instances for each thread.

To use this class, first create an instance using the default constructor or initialize the instance with a PatternCache of your choosing using the alternate constructor. The default cache used by Perl5Util is a PatternCacheLRU of capacity GenericPatternCache.DEFAULT_CAPACITY. You may want to create a cache with a different capacity, a different cache replacement policy, or even devise your own PatternCache implementation. The PatternCacheLRU is probably the best general purpose pattern cache, but your specific application may be better served by a different cache replacement policy. You should remember that you can front-load a cache with all the patterns you will be using before initializing a Perl5Util instance, or you can just let Perl5Util fill the cache as you use it.

You might use the class as follows:

 Perl5Util util = new Perl5Util();
 String line;
 DataInputStream input;
 PrintStream output;
 
 // Initialization of input and output omitted
 while((line = input.readLine()) != null) {
     // First find the line with the string we want to substitute because
     // it is cheaper than blindly substituting each line.
     if(util.match("/HREF=\"description1.html\"/")) {
        line = util.substitute("s/description1\\.html/about1.html/", line);
     }
    output.println(line);
 }
 

A couple of things to remember when using this class are that the match() methods have the same meaning as Perl5Matcher.contains() and =~ m/pattern/ in Perl. The methods are named match to more closely associate them with Perl and to differentiate them from Perl5Matcher.matches(). A further thing to keep in mind is that the MalformedPerl5PatternException class is derived from RuntimeException which means you DON'T have to catch it. The reasoning behind this is that you will detect your regular expression mistakes as you write and debug your program when a MalformedPerl5PatternException is thrown during a test run. However, we STRONGLY recommend that you ALWAYS catch MalformedPerl5PatternException whenever you deal with a DYNAMICALLY created pattern. Relying on a fatal MalformedPerl5PatternException being thrown to detect errors while debugging is only useful for dealing with static patterns, that is, actual pregenerated strings present in your program. Patterns created from user input or some other dynamic method CANNOT be relied upon to be correct and MUST be handled by catching MalformedPerl5PatternException for your programs to be robust.

Finally, as a convenience Perl5Util implements the MatchResult interface. The methods are merely wrappers which call the corresponding method of the last MatchResult found (which can be accessed with getMatch() by a match or substitution (or even a split, but this isn't particularly useful).

Since:
1.0
Version:
2.0.6
Author:
Daniel F. Savarese
See Also:
MalformedPerl5PatternException, PatternCache, PatternCacheLRU, MatchResult

Field Summary
static int SPLIT_ALL
          A constant passed to the split() methods indicating that all occurrences of a pattern should be used to split a string.
 
Constructor Summary
Perl5Util()
          Default constructor for Perl5Util.
Perl5Util(PatternCache cache)
          A secondary constructor for Perl5Util.
 
Method Summary
 int begin(int group)
          Returns the begin offset of the subgroup of the last match found relative the beginning of the match.
 int beginOffset(int group)
          Returns an offset marking the beginning of the last pattern match found relative to the beginning of the input from which the match was extracted.
 int end(int group)
          Returns the end offset of the subgroup of the last match found relative the beginning of the match.
 int endOffset(int group)
          Returns an offset marking the end of the last pattern match found relative to the beginning of the input from which the match was extracted.
 MatchResult getMatch()
          Returns the last match found by a call to a match(), substitute(), or split() method.
 java.lang.String group(int group)
          Returns the contents of the parenthesized subgroups of the last match found according to the behavior dictated by the MatchResult interface.
 int groups()
           
 int length()
          Returns the length of the last match found.
 boolean match(java.lang.String pattern, char[] input)
          Searches for the first pattern match somewhere in a character array taking a pattern specified in Perl5 native format:
 boolean match(java.lang.String pattern, PatternMatcherInput input)
          Searches for the next pattern match somewhere in a org.apache.oro.text.regex.PatternMatcherInput instance, taking a pattern specified in Perl5 native format:
 boolean match(java.lang.String pattern, java.lang.String input)
          Searches for the first pattern match in a String taking a pattern specified in Perl5 native format:
 java.lang.String postMatch()
          Returns the part of the input following the last match found.
 char[] postMatchCharArray()
          Returns the part of the input following the last match found as a char array.
 java.lang.String preMatch()
          Returns the part of the input preceding the last match found.
 char[] preMatchCharArray()
          Returns the part of the input preceding the last match found as a char array.
 void split(java.util.Collection results, java.lang.String input)
          Splits input in the default Perl manner, splitting on all whitespace.
 void split(java.util.Collection results, java.lang.String pattern, java.lang.String input)
          This method is identical to calling:
 void split(java.util.Collection results, java.lang.String pattern, java.lang.String input, int limit)
          Splits a String into strings that are appended to a List, but no more than a specified limit.
 java.util.Vector split(java.lang.String input)
          Deprecated. Use split(Collection results, String input) instead.
 java.util.Vector split(java.lang.String pattern, java.lang.String input)
          Deprecated. Use split(Collection results, String pattern, String input) instead.
 java.util.Vector split(java.lang.String pattern, java.lang.String input, int limit)
          Deprecated. Use split(Collection results, String pattern, String input, int limit) instead.
 int substitute(java.lang.StringBuffer result, java.lang.String expression, java.lang.String input)
          Substitutes a pattern in a given input with a replacement string.
 java.lang.String substitute(java.lang.String expression, java.lang.String input)
          Substitutes a pattern in a given input with a replacement string.
 java.lang.String toString()
          Returns the same as group(0).
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

SPLIT_ALL

public static final int SPLIT_ALL
A constant passed to the split() methods indicating that all occurrences of a pattern should be used to split a string.
Constructor Detail

Perl5Util

public Perl5Util(PatternCache cache)
A secondary constructor for Perl5Util. It initializes the Perl5Matcher used by the class to perform matching operations, but requires the programmer to provide a PatternCache instance for the class to use to compile and store regular expressions. You would want to use this constructor if you want to change the capacity or policy of the cache used. Example uses might be:
 // We know we're going to use close to 50 expressions a whole lot, so
 // we create a cache of the proper size.
 util = new Perl5Util(new PatternCacheLRU(50));
 
or
 // We're only going to use a few expressions and know that second-chance
 // fifo is best suited to the order in which we are using the patterns.
 util = new Perl5Util(new PatternCacheFIFO2(10));
 

Perl5Util

public Perl5Util()
Default constructor for Perl5Util. This initializes the Perl5Matcher used by the class to perform matching operations and creates a default PatternCacheLRU instance to use to compile and cache regular expressions. The size of this cache is GenericPatternCache.DEFAULT_CAPACITY.
Method Detail

match

public boolean match(java.lang.String pattern,
                     char[] input)
              throws MalformedPerl5PatternException
Searches for the first pattern match somewhere in a character array taking a pattern specified in Perl5 native format:
 [m]/pattern/[i][m][s][x]
 
The m prefix is optional and the meaning of the optional trailing options are:
i
case insensitive match
m
treat the input as consisting of multiple lines
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

If the input contains the pattern, the org.apache.oro.text.regex.MatchResult can be obtained by calling getMatch(). However, Perl5Util implements the MatchResult interface as a wrapper around the last MatchResult found, so you can call its methods to access match information.

Parameters:
pattern - The pattern to search for.
input - The char[] input to search.
Returns:
True if the input contains the pattern, false otherwise.
Throws:
MalformedPerl5PatternException - If there is an error in the pattern. You are not forced to catch this exception because it is derived from RuntimeException.

match

public boolean match(java.lang.String pattern,
                     java.lang.String input)
              throws MalformedPerl5PatternException
Searches for the first pattern match in a String taking a pattern specified in Perl5 native format:
 [m]/pattern/[i][m][s][x]
 
The m prefix is optional and the meaning of the optional trailing options are:
i
case insensitive match
m
treat the input as consisting of multiple lines
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

If the input contains the pattern, the MatchResult can be obtained by calling getMatch(). However, Perl5Util implements the MatchResult interface as a wrapper around the last MatchResult found, so you can call its methods to access match information.

Parameters:
pattern - The pattern to search for.
input - The String input to search.
Returns:
True if the input contains the pattern, false otherwise.
Throws:
MalformedPerl5PatternException - If there is an error in the pattern. You are not forced to catch this exception because it is derived from RuntimeException.

match

public boolean match(java.lang.String pattern,
                     PatternMatcherInput input)
              throws MalformedPerl5PatternException
Searches for the next pattern match somewhere in a org.apache.oro.text.regex.PatternMatcherInput instance, taking a pattern specified in Perl5 native format:
 [m]/pattern/[i][m][s][x]
 
The m prefix is optional and the meaning of the optional trailing options are:
i
case insensitive match
m
treat the input as consisting of multiple lines
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

If the input contains the pattern, the MatchResult can be obtained by calling getMatch(). However, Perl5Util implements the MatchResult interface as a wrapper around the last MatchResult found, so you can call its methods to access match information. After the call to this method, the PatternMatcherInput current offset is advanced to the end of the match, so you can use it to repeatedly search for expressions in the entire input using a while loop as explained in the PatternMatcherInput documentation.

Parameters:
pattern - The pattern to search for.
input - The PatternMatcherInput to search.
Returns:
True if the input contains the pattern, false otherwise.
Throws:
MalformedPerl5PatternException - If there is an error in the pattern. You are not forced to catch this exception because it is derived from RuntimeException.

getMatch

public MatchResult getMatch()
Returns the last match found by a call to a match(), substitute(), or split() method. This method is only intended for use to retrieve a match found by the last match found by a match() method. This method should be used when you want to save MatchResult instances. Otherwise, for simply accessing match information, it is more convenient to use the Perl5Util methods implementing the MatchResult interface.

Returns:
The org.apache.oro.text.regex.MatchResult instance containing the last match found.

substitute

public int substitute(java.lang.StringBuffer result,
                      java.lang.String expression,
                      java.lang.String input)
               throws MalformedPerl5PatternException
Substitutes a pattern in a given input with a replacement string. The substitution expression is specified in Perl5 native format:
 s/pattern/replacement/[g][i][m][o][s][x]
 
The s prefix is mandatory and the meaning of the optional trailing options are:
g
Substitute all occurrences of pattern with replacement. The default is to replace only the first occurrence.
i
perform a case insensitive match
m
treat the input as consisting of multiple lines
o
If variable interopolation is used, only evaluate the interpolation once (the first time). This is equivalent to using a numInterpolations argument of 1 in Util.substitute(). The default is to compute each interpolation independently. See Util.substitute() and Perl5Substitution for more details on variable interpolation in substitutions.
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes. This is helpful to avoid backslashing. For example, using slashes you would have to do:
 numSubs = util.substitute(result, "s/foo\\/bar/goo\\/\\/baz/", input);
 
when you could more easily write:
 numSubs = util.substitute(result, "s#foo/bar#goo//baz#", input);
 
where the hashmarks are used instead of slashes.

There is a special case of backslashing that you need to pay attention to. As demonstrated above, to denote a delimiter in the substituted string it must be backslashed. However, this can be a problem when you want to denote a backslash at the end of the substituted string. As of PerlTools 1.3, a new means of handling this situation has been implemented. In previous versions, the behavior was that

"... a double backslash (quadrupled in the Java String) always represents two backslashes unless the second backslash is followed by the delimiter, in which case it represents a single backslash."

The new behavior is that a backslash is always a backslash in the substitution portion of the expression unless it is used to escape a delimiter. A backslash is considered to escape a delimiter if an even number of contiguous backslashes preceed the backslash and the delimiter following the backslash is not the FINAL delimiter in the expression. Therefore, backslashes preceding final delimiters are never considered to escape the delimiter. The following, which used to be an invalid expression and require a special-case extra backslash, will now replace all instances of / with \:

 numSubs = util.substitute(result, "s#/#\\#g", input);
 

Parameters:
result - The StringBuffer in which to store the result of the substitutions. The buffer is only appended to.
expression - The Perl5 substitution regular expression.
input - The input on which to perform substitutions.
Returns:
The number of substitutions made.
Throws:
MalformedPerl5PatternException - If there is an error in the expression. You are not forced to catch this exception because it is derived from RuntimeException.
Since:
2.0.6

substitute

public java.lang.String substitute(java.lang.String expression,
                                   java.lang.String input)
                            throws MalformedPerl5PatternException
Substitutes a pattern in a given input with a replacement string. The substitution expression is specified in Perl5 native format.
Calling this method is the same as:
      String result;
      StringBuffer buffer = new StringBuffer();
      perl.substitute(buffer, expression, input);
      result = buffer.toString();
     
Parameters:
expression - The Perl5 substitution regular expression.
input - The input on which to perform substitutions.
Returns:
The input as a String after substitutions have been performed.
Throws:
MalformedPerl5PatternException - If there is an error in the expression. You are not forced to catch this exception because it is derived from RuntimeException.
Since:
1.0
See Also:
substitute(java.lang.StringBuffer, java.lang.String, java.lang.String)

split

public void split(java.util.Collection results,
                  java.lang.String pattern,
                  java.lang.String input,
                  int limit)
           throws MalformedPerl5PatternException
Splits a String into strings that are appended to a List, but no more than a specified limit. The String is split using a regular expression as the delimiter. The regular expression is a pattern specified in Perl5 native format:
 [m]/pattern/[i][m][s][x]
 
The m prefix is optional and the meaning of the optional trailing options are:
i
case insensitive match
m
treat the input as consisting of multiple lines
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

The limit parameter causes the string to be split on at most the first limit - 1 number of pattern occurences.

Of special note is that this split method performs EXACTLY the same as the Perl split() function. In other words, if the split pattern contains parentheses, additional Vector elements are created from each of the matching subgroups in the pattern. Using an example similar to the one from the Camel book:

 split(list, "/([,-])/", "8-12,15,18")
 
produces the Vector containing:
 { "8", "-", "12", ",", "15", ",", "18" }
 
The Util.split() method does NOT implement this particular behavior because it is intended to be usable with Pattern instances other than Perl5Pattern.

Parameters:
results - A List to which the substrings of the input that occur between the regular expression delimiter occurences are appended. The input will not be split into any more substrings than the specified limit. A way of thinking of this is that only the first limit - 1 matches of the delimiting regular expression will be used to split the input.
pattern - The regular expression to use as a split delimiter.
input - The String to split.
limit - The limit on the size of the returned Vector. Values <= 0 produce the same behavior as the SPLIT_ALL constant which causes the limit to be ignored and splits to be performed on all occurrences of the pattern. You should use the SPLIT_ALL constant to achieve this behavior instead of relying on the default behavior associated with non-positive limit values.
Throws:
MalformedPerl5PatternException - If there is an error in the expression. You are not forced to catch this exception because it is derived from RuntimeException.

split

public void split(java.util.Collection results,
                  java.lang.String pattern,
                  java.lang.String input)
           throws MalformedPerl5PatternException
This method is identical to calling:
 split(results, pattern, input, SPLIT_ALL);
 

split

public void split(java.util.Collection results,
                  java.lang.String input)
           throws MalformedPerl5PatternException
Splits input in the default Perl manner, splitting on all whitespace. This method is identical to calling:
 split(results, "/\\s+/", input);
 

split

public java.util.Vector split(java.lang.String pattern,
                              java.lang.String input,
                              int limit)
                       throws MalformedPerl5PatternException
Deprecated. Use split(Collection results, String pattern, String input, int limit) instead.

Splits a String into strings contained in a Vector of size no greater than a specified limit. The String is split using a regular expression as the delimiter. The regular expression is a pattern specified in Perl5 native format:
 [m]/pattern/[i][m][s][x]
 
The m prefix is optional and the meaning of the optional trailing options are:
i
case insensitive match
m
treat the input as consisting of multiple lines
s
treat the input as consisting of a single line
x
enable extended expression syntax incorporating whitespace and comments
As with Perl, any non-alphanumeric character can be used in lieu of the slashes.

The limit parameter causes the string to be split on at most the first limit - 1 number of pattern occurences.

Of special note is that this split method performs EXACTLY the same as the Perl split() function. In other words, if the split pattern contains parentheses, additional Vector elements are created from each of the matching subgroups in the pattern. Using an example similar to the one from the Camel book:

 split("/([,-])/", "8-12,15,18")
 
produces the Vector containing:
 { "8", "-", "12", ",", "15", ",", "18" }
 
The Util.split() method does NOT implement this particular behavior because it is intended to be usable with Pattern instances other than Perl5Pattern.

Parameters:
pattern - The regular expression to use as a split delimiter.
input - The String to split.
limit - The limit on the size of the returned Vector. Values <= 0 produce the same behavior as the SPLIT_ALL constant which causes the limit to be ignored and splits to be performed on all occurrences of the pattern. You should use the SPLIT_ALL constant to achieve this behavior instead of relying on the default behavior associated with non-positive limit values.
Returns:
A Vector containing the substrings of the input that occur between the regular expression delimiter occurences. The input will not be split into any more substrings than the specified limit. A way of thinking of this is that only the first limit - 1 matches of the delimiting regular expression will be used to split the input.
Throws:
MalformedPerl5PatternException - If there is an error in the expression. You are not forced to catch this exception because it is derived from RuntimeException.

split

public java.util.Vector split(java.lang.String pattern,
                              java.lang.String input)
                       throws MalformedPerl5PatternException
Deprecated. Use split(Collection results, String pattern, String input) instead.

This method is identical to calling:
 split(pattern, input, SPLIT_ALL);
 

split

public java.util.Vector split(java.lang.String input)
                       throws MalformedPerl5PatternException
Deprecated. Use split(Collection results, String input) instead.

Splits input in the default Perl manner, splitting on all whitespace. This method is identical to calling:
 split("/\\s+/", input);
 

length

public int length()
Returns the length of the last match found.

Specified by:
length in interface MatchResult
Returns:
The length of the last match found.

groups

public int groups()
Specified by:
groups in interface MatchResult
Returns:
The number of groups contained in the last match found. This number includes the 0th group. In other words, the result refers to the number of parenthesized subgroups plus the entire match itself.

group

public java.lang.String group(int group)
Returns the contents of the parenthesized subgroups of the last match found according to the behavior dictated by the MatchResult interface.

Specified by:
group in interface MatchResult
Parameters:
group - The pattern subgroup to return.
Returns:
A string containing the indicated pattern subgroup. Group 0 always refers to the entire match. If a group was never matched, it returns null. This is not to be confused with a group matching the null string, which will return a String of length 0.

begin

public int begin(int group)
Returns the begin offset of the subgroup of the last match found relative the beginning of the match.

Specified by:
begin in interface MatchResult
Parameters:
group - The pattern subgroup.
Returns:
The offset into group 0 of the first token in the indicated pattern subgroup. If a group was never matched or does not exist, returns -1. Be aware that a group that matches the null string at the end of a match will have an offset equal to the length of the string, so you shouldn't blindly use the offset to index an array or String.

end

public int end(int group)
Returns the end offset of the subgroup of the last match found relative the beginning of the match.

Specified by:
end in interface MatchResult
Parameters:
group - The pattern subgroup.
Returns:
Returns one plus the offset into group 0 of the last token in the indicated pattern subgroup. If a group was never matched or does not exist, returns -1. A group matching the null string will return its start offset.

beginOffset

public int beginOffset(int group)
Returns an offset marking the beginning of the last pattern match found relative to the beginning of the input from which the match was extracted.

Specified by:
beginOffset in interface MatchResult
Parameters:
group - The pattern subgroup.
Returns:
The offset of the first token in the indicated pattern subgroup. If a group was never matched or does not exist, returns -1.

endOffset

public int endOffset(int group)
Returns an offset marking the end of the last pattern match found relative to the beginning of the input from which the match was extracted.

Specified by:
endOffset in interface MatchResult
Parameters:
group - The pattern subgroup.
Returns:
Returns one plus the offset of the last token in the indicated pattern subgroup. If a group was never matched or does not exist, returns -1. A group matching the null string will return its start offset.

toString

public java.lang.String toString()
Returns the same as group(0).

Specified by:
toString in interface MatchResult
Overrides:
toString in class java.lang.Object
Returns:
A string containing the entire match.

preMatch

public java.lang.String preMatch()
Returns the part of the input preceding the last match found.

Returns:
The part of the input following the last match found.

postMatch

public java.lang.String postMatch()
Returns the part of the input following the last match found.

Returns:
The part of the input following the last match found.

preMatchCharArray

public char[] preMatchCharArray()
Returns the part of the input preceding the last match found as a char array. This method eliminates the extra buffer copying caused by preMatch().toCharArray().

Returns:
The part of the input following the last match found as a char[]. If the result is of zero length, returns null instead of a zero length array.

postMatchCharArray

public char[] postMatchCharArray()
Returns the part of the input following the last match found as a char array. This method eliminates the extra buffer copying caused by preMatch().toCharArray().

Returns:
The part of the input following the last match found as a char[]. If the result is of zero length, returns null instead of a zero length array.

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