perl5util.java

java实现正则表达式的代码

/*
 * $Id: Perl5Util.java,v 1.19 2003/11/07 20:16:25 dfs Exp $
 *
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 * The Apache Software License, Version 1.1
 *
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 * reserved.
 *
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 * modification, are permitted provided that the following conditions
 * are met:
 *
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package org.apache.oro.text.perl;

import java.util.*;

import org.apache.oro.text.*;
import org.apache.oro.text.regex.*;
import org.apache.oro.util.*;

/**
 * This is a utility class implementing the 3 most common Perl5 operations
 * involving regular expressions:
 * <ul>
 * <li> [m]/pattern/[i][m][s][x],
 * <li> s/pattern/replacement/[g][i][m][o][s][x],
 * <li> and split().
 * </ul>
 * As with Perl, any non-alphanumeric character can be used in lieu of
 * the slashes.
 *  <p>
 * 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
 * {@link 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.
 * <p>
 * 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.
 * <p>
 * You might use the class as follows:
 * <pre>
 * 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);
 * }
 * </pre>
 * <p>
 * A couple of things to remember when using this class are that the
 * {@link #match match()} methods have the same meaning as
 * {@link org.apache.oro.text.regex.Perl5Matcher#contains
 *  Perl5Matcher.contains()}
 * and <code>=~ m/pattern/</code> in Perl.  The methods are named match
 * to more closely associate them with Perl and to differentiate them
 * from {@link org.apache.oro.text.regex.Perl5Matcher#matches
 * Perl5Matcher.matches()}.
 * A further thing to keep in mind is that the
 * {@link 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.
 * <p>
 * Finally, as a convenience Perl5Util implements 
 * the {@link org.apache.oro.text.regex.MatchResult MatchResult} interface.
 * The methods are merely wrappers which call the corresponding method of
 * the last {@link org.apache.oro.text.regex.MatchResult MatchResult}
 * found (which can be accessed with {@link #getMatch()}) by a match or
 * substitution (or even a split, but this isn't particularly useful).
 * At the moment, the
 * {@link org.apache.oro.text.regex.MatchResult MatchResult} returned
 * by {@link #getMatch()} is not stored in a thread-local variable.  Therefore
 * concurrent calls to {@link #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 {@link #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.
 *
 * @version @version@
 * @since 1.0
 * @see MalformedPerl5PatternException
 * @see org.apache.oro.text.PatternCache
 * @see org.apache.oro.text.PatternCacheLRU
 * @see org.apache.oro.text.regex.MatchResult
 */
public final class Perl5Util implements MatchResult {
  /** The regular expression to use to parse match expression. */
  private static final String __matchExpression = "m?(\\W)(.*)\\1([imsx]*)";

  /** The pattern cache to compile and store patterns */
  private PatternCache __patternCache;
  /** The hashtable to cache higher-level expressions */
  private Cache __expressionCache;
  /** The pattern matcher to perform matching operations. */
  private Perl5Matcher __matcher;
  /** The compiled match expression parsing regular expression. */
  private Pattern __matchPattern;
  /** The last match from a successful call to a matching method. */
  private MatchResult __lastMatch;
  /**
   * A container for temporarily holding the results of a split before
   * deleting trailing empty fields.
   */
  private ArrayList __splitList;

  /**
   * Keeps track of the original input (for postMatch() and preMatch())
   * methods.  This will be discarded if the preMatch() and postMatch()
   * methods are moved into the MatchResult interface.
   */
  private Object __originalInput;

  /**
   * Keeps track of the begin and end offsets of the original input for
   * the postMatch() and preMatch() methods.
   */
  private int __inputBeginOffset, __inputEndOffset;

  /** Used for default return value of post and pre Match() */
  private static final String __nullString = "";

  /**
   * A constant passed to the {@link #split split()} methods indicating
   * that all occurrences of a pattern should be used to split a string. 
   */
  public static final int SPLIT_ALL = Util.SPLIT_ALL;

  /**
   * 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:
   * <pre>
   * // 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));
   * </pre>
   * or
   * <pre>
   * // 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));
   * </pre>
   */
  public Perl5Util(PatternCache cache) {
    __splitList    = new ArrayList();
    __matcher      = new Perl5Matcher();
    __patternCache = cache;
    __expressionCache = new CacheLRU(cache.capacity());
    __compilePatterns();
  }

  /**
   * 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.
   */
  public Perl5Util() {
    this(new PatternCacheLRU());
  }

  /**
   * Compiles the patterns (currently only the match expression) used to
   * parse Perl5 expressions.  Right now it initializes __matchPattern.
   */
  private void __compilePatterns() {
    Perl5Compiler compiler = new Perl5Compiler();

    try {
      __matchPattern = 
	compiler.compile(__matchExpression, Perl5Compiler.SINGLELINE_MASK);
    } catch(MalformedPatternException e) {
      // This should only happen during debugging.
      //e.printStackTrace();
      throw new RuntimeException(e.getMessage());
    }
  }

  /**
   * 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.
   * <p>
   * @param pattern  The Perl5 match expression to parse.
   * @exception MalformedPerl5PatternException If there is an error parsing
   *            the expression.
   */
  private Pattern __parseMatchExpression(String pattern)
       throws MalformedPerl5PatternException 
  {
    int index, compileOptions;
    String options, regex;
    MatchResult result;
    Object obj;
    Pattern ret;

    obj = __expressionCache.getElement(pattern);

    // Must catch ClassCastException because someone might incorrectly 
    // pass an s/// expression.  try block is cheaper than checking
    // instanceof
    try {
      if(obj != null)
	return (Pattern)obj;
    } catch(ClassCastException e) {
      // Fall through and parse expression
    }

    if(!__matcher.matches(pattern, __matchPattern))
      throw new
	MalformedPerl5PatternException("Invalid expression: " +
				       pattern);

    result = __matcher.getMatch();

    regex = result.group(2);
    compileOptions = Perl5Compiler.DEFAULT_MASK;

    options = result.group(3);

    if(options != null) {
      index = options.length();

      while(index-- > 0) {
	switch(options.charAt(index)) {
	case 'i' :
	  compileOptions |= Perl5Compiler.CASE_INSENSITIVE_MASK;
	  break;
	case 'm' : compileOptions |= Perl5Compiler.MULTILINE_MASK; break;
	case 's' : compileOptions |= Perl5Compiler.SINGLELINE_MASK; break;
	case 'x' : compileOptions |= Perl5Compiler.EXTENDED_MASK; break;
	default  :
	  throw new
	    MalformedPerl5PatternException("Invalid options: " + options);