Class Perl5Util

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

public final class Perl5Util extends 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). At the moment, the MatchResult returned by getMatch() is not stored in a thread-local variable. Therefore concurrent calls to getMatch() will produce unpredictable results. So if your concurrent program requires the match results, you must protect the matching and the result retrieval in a critical section. If you do not need match results, you don't need to do anything special. If you feel the J2SE implementation of getMatch() should use a thread-local variable and obviate the need for a critical section, please express your views on the oro-dev mailing list.

Since:
1.0
See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final Cache
    The hashtable to cache higher-level expressions
    private MatchResult
    The last match from a successful call to a matching method.
    private final Perl5Matcher
    The pattern matcher to perform matching operations.
    private static final String
    The regular expression to use to parse match expression.
    private Pattern
    The compiled match expression parsing regular expression.
    private final PatternCache
    The pattern cache to compile and store patterns
  • Constructor Summary

    Constructors
    Constructor
    Description
    Default constructor for Perl5Util.
    A secondary constructor for Perl5Util.
  • Method Summary

    Modifier and Type
    Method
    Description
    private void
    Compiles the patterns (currently only the match expression) used to parse Perl5 expressions.
    private Pattern
    Parses a match expression and returns a compiled pattern.
    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.
    Returns the last match found by a call to a match(), substitute(), or split() method.
    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
     
    int
    Returns the length of the last match found.
    boolean
    match(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(String pattern, String input)
    Searches for the first pattern match in a String taking a pattern specified in Perl5 native format:
    Returns the same as group(0).

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
  • Field Details

    • __matchExpression

      private static final String __matchExpression
      The regular expression to use to parse match expression.
      See Also:
    • __patternCache

      private final PatternCache __patternCache
      The pattern cache to compile and store patterns
    • __expressionCache

      private final Cache __expressionCache
      The hashtable to cache higher-level expressions
    • __matcher

      private final Perl5Matcher __matcher
      The pattern matcher to perform matching operations.
    • __matchPattern

      private Pattern __matchPattern
      The compiled match expression parsing regular expression.
    • __lastMatch

      private MatchResult __lastMatch
      The last match from a successful call to a matching method.
  • Constructor Details

    • Perl5Util

      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 Details

    • __compilePatterns

      private void __compilePatterns()
      Compiles the patterns (currently only the match expression) used to parse Perl5 expressions. Right now it initializes __matchPattern.
    • __parseMatchExpression

      private Pattern __parseMatchExpression(String pat) throws MalformedPerl5PatternException
      Parses a match expression and returns a compiled pattern. First checks the expression cache and if the pattern is not found, then parses the expression and fetches a compiled pattern from the pattern cache. Otherwise, just uses the pattern found in the expression cache. __matchPattern is used to parse the expression.

      Parameters:
      pat - The Perl5 match expression to parse.
      Throws:
      MalformedPerl5PatternException - If there is an error parsing the expression.
    • match

      public boolean match(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(String pattern, 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.
    • 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.
    • 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 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 String toString()
      Returns the same as group(0).

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