http://wiki.apache.org/nutch/HowToMakeCustomSearch?highlight=%28search%29%7C%28custom%29
Use Case
Suppose we want to search for the author of the website by his email id.
Indexing the email id
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:
<plugin id="index-email" name="Email Indexing Filter" version="1.0.0"
provider-name="swayam">
<runtime>
<library name="EmailIndexingFilterPlugin.jar">
<export name="*" />
</library>
</runtime>
<requires>
<import plugin="nutch-extensionpoints" />
</requires>
<extension id="com.swayam.nutch.plugins.indexfilter.EmailIndexingFilter"
name="Email Indexing Filter"
point="org.apache.nutch.indexer.IndexingFilter">
<implementation id="index-email"
class="com.swayam.nutch.plugins.indexfilter.EmailIndexingFilter" />
</extension>
</plugin>
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.
<property> <name>plugin.includes</name> <value>nutch-extensionpoints|protocol-http|parse-(text|html)|index-(basic|email)|query-(basic|site|url)</value> <description>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. </description> </property>
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.
<plugin
id="query-email"
name="Email Query Filter"
version="1.0.0"
provider-name="swayam">
<runtime>
<library name="EmailQueryFilterPlugin.jar">
<export name="*"/>
</library>
</runtime>
<requires>
<import plugin="nutch-extensionpoints"/>
</requires>
<extension id="com.swayam.nutch.plugins.queryfilter.MyEmailQueryFilter"
name="Email Query Filter"
point="org.apache.nutch.searcher.QueryFilter">
<implementation id="query-email"
class="com.swayam.nutch.plugins.queryfilter.MyEmailQueryFilter">
<parameter name="fields" value="email"/>
</implementation>
</extension>
</plugin>
This line is particularly important:
<parameter name=”fields” value=”email”/>
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.
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:
<!-- <property> <name>query.basic.description.boost</name> <value>1.0</value> <description> Declares a custom field and its boost to be added to the default fields of the Lucene query. </description> </property> -->
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:
<property> <name>query.basic.email.boost</name> <value>1.0</value> <description> Queries the author of the site by his email-id </description> </property>
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/official way is by ant, but I have used maven with the following dependencies:
<project>
...
<dependencies>
...
<!-- nutch -->
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-core</artifactId>
<version>2.4.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.lucene</groupId>
<artifactId>lucene-misc</artifactId>
<version>2.4.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.nutch</groupId>
<artifactId>nutch</artifactId>
<version>1.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.taglibs</groupId>
<artifactId>taglibs-i18n</artifactId>
<version>1.0.N20030822</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.tika</groupId>
<artifactId>tika</artifactId>
<version>0.1-incubating</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>xerces</groupId>
<artifactId>xerces</artifactId>
<version>2.6.2</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>xerces</groupId>
<artifactId>xerces-apis</artifactId>
<version>2.6.2</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.jets3t.service</groupId>
<artifactId>jets3t</artifactId>
<version>0.6.1</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>oro</groupId>
<artifactId>oro</artifactId>
<version>2.0.8</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.ibm.icu</groupId>
<artifactId>icu4j</artifactId>
<version>4.0.1</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-core</artifactId>
<version>0.19.1</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.solr</groupId>
<artifactId>solr-common</artifactId>
<version>1.3.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.solr</groupId>
<artifactId>solrj</artifactId>
<version>1.3.0</version>
<scope>provided</scope>
</dependency>
<!-- end nutch -->
...
</dependencies>
...
</project>