    1   /* PatternMatcherRecycler
    2   *
    3   * $Id: PatternMatcherRecycler.java 4644 2006-09-20 22:40:21Z paul_jack $
    4   *
    5   * Created on Dec 21, 2004
    6   *
    7   * Copyright (C) 2004 Internet Archive.
    8   *
    9   * This file is part of the Heritrix web crawler (crawler.archive.org).
    10  *
    11  * Heritrix is free software; you can redistribute it and/or modify
    12  * it under the terms of the GNU Lesser Public License as published by
    13  * the Free Software Foundation; either version 2.1 of the License, or
    14  * any later version.
    15  *
    16  * Heritrix is distributed in the hope that it will be useful,
    17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
    18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    19  * GNU Lesser Public License for more details.
    20  *
    21  * You should have received a copy of the GNU Lesser Public License
    22  * along with Heritrix; if not, write to the Free Software
    23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    24  */
    25  package org.archive.util;
    26
    27  import java.util.EmptyStackException;
    28  import java.util.Stack;
    29  import java.util.regex.Matcher;
    30  import java.util.regex.Pattern;
    31
    32  /***
    33   * Utility class to retain a compiled Pattern and multiple corresponding
    34   * Matcher instances for reuse.
    35   *
    36   * @author gojomo
    37   */
    38  public class PatternMatcherRecycler {
    39      /***
    40       * Upper-bound on Matcher Stacks.
    41       * Profiling has the size of these Stacks tending upward over
    42       * the life of a crawl.  TODO: do something better than an
    43       * a coarse upperbound; do something that can get GC'd in
    44       * low-memory conditions.
    45       */
    46      private final static int MAXIMUM_STACK_SIZE = 10;
    47
    48      private Pattern pattern;
    49      private Stack<Matcher> matchers;
    50
    51      public PatternMatcherRecycler(Pattern p) {
    52          this.pattern = p;
    53          this.matchers = new Stack<Matcher>();
    54      }
    55
    56      public Pattern getPattern() {
    57          return this.pattern;
    58      }
    59
    60      /***
    61       * Get a Matcher for the internal Pattern, against the given
    62       * input sequence. Reuse an old Matcher if possible, otherwise
    63       * create a new one.
    64       *
    65       * @param input CharSequence to match
    66       * @return Matcher set against the the input sequence
    67       */
    68      public Matcher getMatcher(CharSequence input) {
    69          if (input == null) {
    70              throw new IllegalArgumentException("CharSequence 'input' must not be null");
    71          }
    72          try {
    73              return ((Matcher)matchers.pop()).reset(input);
    74          } catch (EmptyStackException e) {
    75              return this.pattern.matcher(input);
    76          }
    77      }
    78
    79      /***
    80       * Return the given Matcher to the reuse stack, if stack is
    81       * not already at its maximum size.
    82       *
    83       * @param m the Matcher to save for reuse
    84       */
    85      public void freeMatcher(Matcher m) {
    86          if(this.matchers.size() < MAXIMUM_STACK_SIZE) {
    87              matchers.push(m);
    88          }
    89      }
    90  }
    91