nutch-core/src/main/java/org/apache/nutch/parse/OutlinkExtractor.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.nutch.parse;

import java.lang.invoke.MethodHandles;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hadoop.conf.Configuration;
import org.apache.oro.text.regex.MatchResult;
import org.apache.oro.text.regex.Pattern;
import org.apache.oro.text.regex.PatternCompiler;
import org.apache.oro.text.regex.PatternMatcher;
import org.apache.oro.text.regex.PatternMatcherInput;
import org.apache.oro.text.regex.Perl5Compiler;
import org.apache.oro.text.regex.Perl5Matcher;

/**
 * Extractor to extract {@link org.apache.nutch.parse.Outlink}s / URLs from
 * plain text using Regular Expressions.
 * 
 * @see <a
 *      href="http://wiki.java.net/bin/view/Javapedia/RegularExpressions">Comparison
 *      of different regexp-Implementations </a>
 * @see <a href="http://regex.info/java.html">Overview about Java Regexp APIs
 *      </a>
 * 
 * @author Stephan Strittmatter - http://www.sybit.de
 * @version 1.0
 * @since 0.7
 */
public class OutlinkExtractor {
  private static final Logger LOG = LoggerFactory
      .getLogger(MethodHandles.lookup().lookupClass());

  /**
   * Regex pattern to get URLs within a plain text.
   * 
   * @see <a
   *      href="http://www.truerwords.net/articles/ut/urlactivation.html">http://www.truerwords.net/articles/ut/urlactivation.html

   *      </a>
   */
  private static final String URL_PATTERN = "([A-Za-z][A-Za-z0-9+.-]{1,120}:[A-Za-z0-9/](([A-Za-z0-9$_.+!*,;/?:@&~=-])|%[A-Fa-f0-9]{2}){1,333}(#([a-zA-Z0-9][a-zA-Z0-9$_.+!*,;/?:@&~=%-]{0,1000}))?)";

  /**
   * Extracts <code>Outlink</code> from given plain text. Applying this method
   * to non-plain-text can result in extremely lengthy runtimes for parasitic
   * cases (postscript is a known example).
   * 
   * @param plainText
   *          the plain text from which URLs should be extracted.
   * 
   * @return Array of <code>Outlink</code>s within found in plainText
   */
  public static Outlink[] getOutlinks(final String plainText, Configuration conf) {
    return OutlinkExtractor.getOutlinks(plainText, "", conf);
  }

  /**
   * Extracts <code>Outlink</code> from given plain text and adds anchor to the
   * extracted <code>Outlink</code>s
   * 
   * @param plainText
   *          the plain text from wich URLs should be extracted.
   * @param anchor
   *          the anchor of the url
   * 
   * @return Array of <code>Outlink</code>s within found in plainText
   */
  public static Outlink[] getOutlinks(final String plainText, String anchor,
      Configuration conf) {
    long start = System.currentTimeMillis();
    final List<Outlink> outlinks = new ArrayList<>();

    try {
      final PatternCompiler cp = new Perl5Compiler();
      final Pattern pattern = cp.compile(URL_PATTERN,
          Perl5Compiler.CASE_INSENSITIVE_MASK | Perl5Compiler.READ_ONLY_MASK
              | Perl5Compiler.MULTILINE_MASK);
      final PatternMatcher matcher = new Perl5Matcher();

      final PatternMatcherInput input = new PatternMatcherInput(plainText);

      MatchResult result;
      String url;

      // loop the matches
      while (matcher.contains(input, pattern)) {
        // if this is taking too long, stop matching
        // (SHOULD really check cpu time used so that heavily loaded systems
        // do not unnecessarily hit this limit.)
        if (System.currentTimeMillis() - start >= 60000L) {
          if (LOG.isWarnEnabled()) {
            LOG.warn("Time limit exceeded for getOutLinks");
          }
          break;
        }
        result = matcher.getMatch();
        url = result.group(0);
        try {
          outlinks.add(new Outlink(url, anchor));
        } catch (MalformedURLException mue) {
          LOG.warn("Invalid url: '" + url + "', skipping.");
        }
      }
    } catch (Exception ex) {
      // if the matcher fails (perhaps a malformed URL) we just log it and move
      // on
      if (LOG.isErrorEnabled()) {
        LOG.error("getOutlinks", ex);
      }
    }

    final Outlink[] retval;

    // create array of the Outlinks
    if (outlinks != null && outlinks.size() > 0) {
      retval = outlinks.toArray(new Outlink[0]);
    } else {
      retval = new Outlink[0];
    }

    return retval;
  }

}