code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.regexp;
  
  import java.util.regex.Matcher;
  
  import com.puppycrawl.tools.checkstyle.api.FileText;
  import com.puppycrawl.tools.checkstyle.api.LineColumn;
  
  /**
   * A detector that matches across multiple lines.
   */
  class MultilineDetector {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_REGEXP_EXCEEDED = "regexp.exceeded";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_REGEXP_MINIMUM = "regexp.minimum";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_EMPTY = "regexp.empty";
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_STACKOVERFLOW = "regexp.StackOverflowError";
  
      /** The detection options to use. */
      private final DetectorOptions options;
      /** Tracks the number of matches. */
      private int currentMatches;
      /** The matcher. */
      private Matcher matcher;
      /** The file text content. */
      private FileText text;
  
      /**
       * Creates an instance.
       *
       * @param options the options to use.
       */
      /* package */ MultilineDetector(DetectorOptions options) {
          this.options = options;
      }
  
      /**
       * Processes an entire text file looking for matches.
       *
       * @param fileText the text to process
       */
      public void processLines(FileText fileText) {
          text = new FileText(fileText);
          resetState();
  
          final String format = options.getFormat();
          if (format == null || format.isEmpty()) {
              options.getReporter().log(1, MSG_EMPTY);
          }
          else {
              matcher = options.getPattern().matcher(fileText.getFullText());
              findMatch();
              finish();
          }
      }
  
      /** Method that finds the matches. */
      private void findMatch() {
          try {
              boolean foundMatch = matcher.find();
  
              while (foundMatch) {
                  currentMatches++;
                  if (currentMatches > options.getMaximum()) {
                      final LineColumn start = text.lineColumn(matcher.start());
                      if (options.getMessage().isEmpty()) {
                          options.getReporter().log(start.getLine(),
                                  MSG_REGEXP_EXCEEDED, matcher.pattern().toString());
                      }
                      else {
                          options.getReporter()
                                  .log(start.getLine(), options.getMessage());
                      }
                  }
                  foundMatch = matcher.find();
              }
          }
          // see http://bugs.java.com/bugdatabase/view_bug.do?bug_id=6337993 et al.
          catch (StackOverflowError ignored) {
              // OK http://blog.igorminar.com/2008/05/catching-stackoverflowerror-and-bug-in.html
              // http://programmers.stackexchange.com/questions/
              //        209099/is-it-ever-okay-to-catch-stackoverflowerror-in-java
              options.getReporter().log(1, MSG_STACKOVERFLOW, matcher.pattern().toString());
          }
      }
  
      /** Perform processing at the end of a set of lines. */
      private void finish() {
          if (currentMatches < options.getMinimum()) {
              if (options.getMessage().isEmpty()) {
                  options.getReporter().log(1, MSG_REGEXP_MINIMUM,
                          options.getMinimum(), options.getFormat());
              }
              else {
                  options.getReporter().log(1, options.getMessage());
              }
          }
      }
  
      /**
       * Reset the state of the detector.
       */
      private void resetState() {
          currentMatches = 0;
      }
  
  }
  