RobotsFilter.java

/**
 * Licensed to DigitalPebble Ltd under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * DigitalPebble 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 com.digitalpebble.stormcrawler.filtering.robots;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.Map;

import com.digitalpebble.stormcrawler.Metadata;
import com.digitalpebble.stormcrawler.filtering.URLFilter;
import com.digitalpebble.stormcrawler.protocol.HttpRobotRulesParser;
import com.digitalpebble.stormcrawler.protocol.ProtocolFactory;
import com.fasterxml.jackson.databind.JsonNode;

import org.apache.storm.Config;
import crawlercommons.robots.BaseRobotRules;

/**
 * URLFilter which discards URLs based on the robots.txt directives. This is
 * meant to be used on small, limited crawls where the number of hosts is
 * finite. Using this on a larger or open crawl would have a negative impact on
 * performance as the filter would try to retrieve the robots.txt files for any
 * host found.
 **/
public class RobotsFilter implements URLFilter {

    private com.digitalpebble.stormcrawler.protocol.HttpRobotRulesParser robots;
    private ProtocolFactory factory;
    private boolean limitToSameHost = false;

    @Override
    public String filter(URL sourceUrl, Metadata sourceMetadata,
            String urlToFilter) {
        URL target;
        try {
            target = new URL(urlToFilter);
        } catch (MalformedURLException e) {
            return null;
        }

        // check whether the source and target have the same hostname
        if (limitToSameHost) {
            if (!target.getHost().equalsIgnoreCase(sourceUrl.getHost())) {
                return urlToFilter;
            }
        }

        BaseRobotRules rules = robots.getRobotRulesSet(
                factory.getProtocol(target), urlToFilter);
        if (!rules.isAllowed(urlToFilter)) {
            return null;
        }
        return urlToFilter;
    }

    @Override
    public void configure(Map stormConf, JsonNode filterParams) {
        Config conf = new Config();
        conf.putAll(stormConf);
        factory = new ProtocolFactory(conf);
        robots = new HttpRobotRulesParser(conf);

        JsonNode node = filterParams.get("limitToSameHost");
        if (node != null && node.isBoolean()) {
            limitToSameHost = node.booleanValue();
        }
    }

}