[How to] Make custom search with Nutch(v 1.0)?

Posted by {"name"=>"Palash Ray", "email"=>"paawak@gmail.com", "url"=>"https://www.linkedin.com/in/palash-ray/"} on April 29, 2009 · 6 mins read

What is Nutch?

Nutch is an open source web crawler + search engine based on Lucene. These are a few things that make it great:

  1. Open source
  2. Has a web-crawler which understands and indexes html, rtf and pdf format + all links that it might encounter
  3. Its search engine is based on Lucene
  4. Has a plugin based architecture, which means we can have our own plugins for indexing and searching, without a single line of code change to the core nutch.jar
  5. Uses Hadoop for storing indexes, so its pretty scalable

Use case

Suppose we want to search for the author of the website by his email id.

First things first: lets index our custom data

Before we can search for our custom data, we need to index it. Nutch has a plugin architecture very similar to that of Eclipse. We can write our own plugin for indexing. Here is the source code:

package com.swayam.nutch.plugins.indexfilter;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Text;
import org.apache.nutch.crawl.CrawlDatum;
import org.apache.nutch.crawl.Inlinks;
import org.apache.nutch.indexer.IndexingException;
import org.apache.nutch.indexer.IndexingFilter;
import org.apache.nutch.indexer.NutchDocument;
import org.apache.nutch.indexer.lucene.LuceneWriter;
import org.apache.nutch.parse.Parse;
/**
 *@author paawak
 */
public class EmailIndexingFilter implements IndexingFilter {
    private static final Log LOG = LogFactory.getLog(EmailIndexingFilter.class);
    private static final String KEY_CREATOR_EMAIL = "email";
    private Configuration conf;
    public NutchDocument filter(NutchDocument doc, Parse parse, Text url,
            CrawlDatum datum, Inlinks inlinks) throws IndexingException {
        // look up email of the author based on the url of the site
        String creatorEmail = EmailLookup.getCreatorEmail(url.toString());
        LOG.info("######## creatorEmail = " + creatorEmail);
        if (creatorEmail != null) {
            doc.add(KEY_CREATOR_EMAIL, creatorEmail);
        }
        return doc;
    }
    public void addIndexBackendOptions(Configuration conf) {
        LuceneWriter.addFieldOptions(KEY_CREATOR_EMAIL, LuceneWriter.STORE.YES,
                LuceneWriter.INDEX.TOKENIZED, conf);
    }
    public Configuration getConf() {
        return conf;
    }
    public void setConf(Configuration conf) {
        this.conf = conf;
    }
}

Also, you need to create a plugin.xml:

This done, create a new folder in the $NUTCH_HOME/plugins and put the jar and the plugin.xml there.
Now we have to activate this plugin. To do this, we have to edit the conf/nutch-site.xml.


  plugin.includes
  nutch-extensionpoints|protocol-http|parse-(text|html)|index-(basic|email)|query-(basic|site|url)
  Regular expression naming plugin id names to
  include.  Any plugin not matching this expression is excluded.
  In any case you need at least include the nutch-extensionpoints plugin. By
  default Nutch includes crawling just HTML and plain text via HTTP,
  and basic indexing and search plugins.

Now, how do I search my indexed data?

Option 1 [cumbersome]:

Add my own query plugin:

package com.swayam.nutch.plugins.queryfilter;
import org.apache.nutch.searcher.FieldQueryFilter;
/**
 *@author paawak
 */
public class MyEmailQueryFilter extends FieldQueryFilter {
    public MyEmailQueryFilter() {
        super("email");
    }
}

Do not forget to edit the plugin.xml.

This line is particularly important:

If you skip this line, you will never be able to see this in search results.
The only catch here is you have to prepend the keyword email: to the search key. For example, if you want to search for jsmith@mydomain.com, you have to search for email:jsmith@mydomain.com or email:jsmith.
There is an easier and more elegant way :), read on...

Option 2 [smart]

Use the existing query-basic plugin.
This involves editing just one file: conf/nutch-default.xml.
In the default distribution, you can see some commented lines like this:

All you have to do is un-comment them and put your custom field, email, in our case in place of description. The resulting fragment will look like:


  query.basic.email.boost
  1.0
   Queries the author of the site by his email-id

With this while looking for jsmith@mydomain.com, you can simply enter jsmith@mydomain.com or a part the name like jsmit.

Building a Nutch plugin

The preferred way is by ant, but I have used maven with the following dependencies:


...
	
		...
		
		
			org.apache.lucene
      		lucene-core
      		2.4.0
      		provided
		
		
			org.apache.lucene
      		lucene-misc
      		2.4.0
      		provided
		
		
			org.apache.nutch
      		nutch
      		1.0
      		provided
		
		
			org.apache.taglibs
      		taglibs-i18n
      		1.0.N20030822
      		provided
		
		
			org.apache.tika
			tika
			0.1-incubating
			provided
		
		
			xerces
			xerces
			2.6.2
			provided
		
		
			xerces
			xerces-apis
			2.6.2
			provided
		
		
			org.jets3t.service
			jets3t
			0.6.1
			provided
		
		
			oro
  			oro
  			2.0.8
  			provided
		
		
			com.ibm.icu
  			icu4j
  			4.0.1
  			provided
		
		
			org.apache.hadoop
  			hadoop-core
  			0.19.1
  			provided
		
		
			org.apache.solr
  			solr-common
  			1.3.0
  			provided
		
		
			org.apache.solr
  			solrj
  			1.3.0
  			provided
		
		
	    ...
	
...

Useful links

Be warned that these are a bit out dated, so they may not be correct verbatim.

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