Apache Nutch with Custom Parser

Table of Content

1 Introduction
2 Use Case
3 Solution
4 Conclusion
5 References

Introduction

This is third in the multi part series that talks about Apache Nutch with custom parser. Now let’s see how to create a custom parser plug-in and configure it with Nutch to scrape content. It is essential to have a basic understanding of Nutch and its configuration which is detailed in our first and second blog, “Apache Nutch – A Web Crawler Framework” and “Apache Nutch with customized Mime – Type” respectively.

Use Case

Let’s reuse RSS feed example discussed in the first blog to understand URL crawling, and indexing documents using custom Feed plug-in, instead of using pre-defined parse-tika plug-in.

What we need to do:

Write a Feed program to parse the content
Prepare metadata files of custom plug-in (plugin.xml and build.xml) with required configuration
Build the custom parser
Reconfigure the parse-plugin.xml with custom parse
Crawl and index the content

Solution

Before solving our use case, let’s get some pre-requisites satisfied. Fortunately, to create custom feed parser plug-in, only a couple of jar files are needed.

Pre-requisites:

Download rome.jar

http://repo1.maven.org/maven2/rome/rome/0.9/rome-0.9.jar

Download jdom.jar

http://repo1.maven.org/maven2/jdom/jdom/1.0/jdom-1.0.jar

Configure other required jars from Nutch library folder

${nutch_home}/lib/nutch1.1.jar
${nutch_home}/lib/hadoop-0.20.2-core.jar
${nutch_home}/lib/commons-logging-1.0.4.jar

Note: Configure all above jars in Eclipse or in any preferable environment, to develop this plug-in.

Write a Feed program to parse the content:

ParseFeed.java

package com.treselle.parse.feed;

import java.io.ByteArrayInputStream;
import java.util.Iterator;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.util.StringUtils;
import org.apache.nutch.metadata.Metadata;
import org.apache.nutch.parse.Outlink;
import org.apache.nutch.parse.ParseData;
import org.apache.nutch.parse.ParseResult;
import org.apache.nutch.parse.ParseStatus;
import org.apache.nutch.parse.ParseText;
import org.apache.nutch.protocol.Content;
import org.apache.nutch.util.EncodingDetector;
import org.xml.sax.InputSource;

import com.sun.syndication.feed.synd.SyndEntry;
import com.sun.syndication.feed.synd.SyndFeed;
import com.sun.syndication.io.SyndFeedInput;

public class ParseFeed implements org.apache.nutch.parse.Parser {
	public static final Log LOG = LogFactory.getLog("com.treselle.parse.feed");
	private Configuration conf = null;
	private String defaultEncoding = null;

	@Override
	public Configuration getConf() {
		return this.conf;
	}

	@Override
	public void setConf(Configuration conf) {
		this.defaultEncoding = conf.get("parser.character.encoding.default",
				"ISO-8859-1");
		this.conf = conf;
	}

	@Override
	public ParseResult getParse(Content content) {
		SyndFeed feed = null;
		ParseResult parseResult = new ParseResult(content.getBaseUrl());

		EncodingDetector detector = new EncodingDetector(this.conf);
		detector.autoDetectClues(content, true);
		String encoding = detector.guessEncoding(content, this.defaultEncoding);
		try {
			String feedContent = new String(content.getContent());
			InputSource input = new InputSource(new ByteArrayInputStream(feedContent.getBytes()));
			input.setEncoding(encoding);
			SyndFeedInput feedInput = new SyndFeedInput();

			feed = feedInput.build(input);
		} catch (Exception e) {
			LOG.warn("Parse failed: url: " + content.getUrl() + ", exception: "	+ StringUtils.stringifyException(e));
			return new ParseStatus(e).getEmptyParseResult(content.getUrl(), getConf());
		}
		List<SyndEntry> entries = feed.getEntries();
		String feedLink = feed.getLink();
		for (Iterator<SyndEntry> i = entries.iterator(); i.hasNext();) {
			SyndEntry entry = i.next();
			addToMap(parseResult, feedLink, entry, content);
		}
		return parseResult;
	}

			/**
* This methods get Metadatas from Each entry (SyndEntry) and add those results with parseResult object
			 * @param parseResult
			 * @param feedLink
			 * @param entry
	 	    	 * @param content
	 */
	private void addToMap(ParseResult parseResult, String feedLink, SyndEntry entry, Content content) {
		LOG.info("The feedlink is " + feedLink);
		String link = entry.getLink();
String title = entry.getTitle();
String description = entry.getDescription().getValue();
		Metadata parseMeta = new Metadata();
		Metadata contentMeta = content.getMetadata();

		LOG.info("entry Link is : " + link);
		LOG.info("entry Title is : " + title);
		LOG.info("entry Description is : " + description);
		LOG.info("entry Updated Date is : " + entry.getUpdatedDate());
		LOG.info("entry published date is : " + entry.getPublishedDate());

		parseMeta.set("title ", title);
		parseMeta.set("description ", description);
		parseMeta.set("linkurl ", link);

		if (entry.getPublishedDate() != null) {
			parseMeta.set("date", entry.getPublishedDate().toString());
		}
		if (entry.getUpdatedDate() != null) {
			parseMeta.set("date", entry.getUpdatedDate().toString());
		}
		LOG.info("Date  " + parseMeta.get("date"));

		parseResult.put(link, new ParseText(description), new ParseData(ParseStatus.STATUS_SUCCESS, title, new Outlink[0], contentMeta, parseMeta));
	}
}

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package com.treselle.parse.feed;

import java.io.ByteArrayInputStream;

import java.util.Iterator;

import java.util.List;

import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.util.StringUtils;

import org.apache.nutch.metadata.Metadata;

import org.apache.nutch.parse.Outlink;

import org.apache.nutch.parse.ParseData;

import org.apache.nutch.parse.ParseResult;

import org.apache.nutch.parse.ParseStatus;

import org.apache.nutch.parse.ParseText;

import org.apache.nutch.protocol.Content;

import org.apache.nutch.util.EncodingDetector;

import org.xml.sax.InputSource;

import com.sun.syndication.feed.synd.SyndEntry;

import com.sun.syndication.feed.synd.SyndFeed;

import com.sun.syndication.io.SyndFeedInput;

public class ParseFeed implements org.apache.nutch.parse.Parser {

public static final Log LOG = LogFactory.getLog("com.treselle.parse.feed");

private Configuration conf = null;

private String defaultEncoding = null;

@Override

public Configuration getConf() {

return this.conf;

}

@Override

public void setConf(Configuration conf) {

this.defaultEncoding = conf.get("parser.character.encoding.default",

"ISO-8859-1");

this.conf = conf;

}

@Override

public ParseResult getParse(Content content) {

SyndFeed feed = null;

ParseResult parseResult = new ParseResult(content.getBaseUrl());

EncodingDetector detector = new EncodingDetector(this.conf);

detector.autoDetectClues(content, true);

String encoding = detector.guessEncoding(content, this.defaultEncoding);

try {

String feedContent = new String(content.getContent());

InputSource input = new InputSource(new ByteArrayInputStream(feedContent.getBytes()));

input.setEncoding(encoding);

SyndFeedInput feedInput = new SyndFeedInput();

feed = feedInput.build(input);

} catch (Exception e) {

LOG.warn("Parse failed: url: " + content.getUrl() + ", exception: " + StringUtils.stringifyException(e));

return new ParseStatus(e).getEmptyParseResult(content.getUrl(), getConf());

}

List<SyndEntry> entries = feed.getEntries();

String feedLink = feed.getLink();

for (Iterator<SyndEntry> i = entries.iterator(); i.hasNext();) {

SyndEntry entry = i.next();

addToMap(parseResult, feedLink, entry, content);

}

return parseResult;

}

/**

* This methods get Metadatas from Each entry (SyndEntry) and add those results with parseResult object

* @param parseResult

* @param feedLink

* @param entry

* @param content

private void addToMap(ParseResult parseResult, String feedLink, SyndEntry entry, Content content) {

LOG.info("The feedlink is " + feedLink);

String link = entry.getLink();

String title = entry.getTitle();

String description = entry.getDescription().getValue();

Metadata parseMeta = new Metadata();

Metadata contentMeta = content.getMetadata();

LOG.info("entry Link is : " + link);

LOG.info("entry Title is : " + title);

LOG.info("entry Description is : " + description);

LOG.info("entry Updated Date is : " + entry.getUpdatedDate());

LOG.info("entry published date is : " + entry.getPublishedDate());

parseMeta.set("title ", title);

parseMeta.set("description ", description);

parseMeta.set("linkurl ", link);

if (entry.getPublishedDate() != null) {

parseMeta.set("date", entry.getPublishedDate().toString());

}

if (entry.getUpdatedDate() != null) {

parseMeta.set("date", entry.getUpdatedDate().toString());

}

LOG.info("Date " + parseMeta.get("date"));

parseResult.put(link, new ParseText(description), new ParseData(ParseStatus.STATUS_SUCCESS, title, new Outlink[0], contentMeta, parseMeta));

}

Compile the Java file and save it as parse-feed.jar and put it in

${nutch_home}/plugins/${plugin_name}/parse-feed.jar directory.

Prepare metadata files:

Using custom plug-in (plugin.xml and build.xml) prepare metadata files with required configuration:

plugin.xml

<?xml version="1.0"?>
<plugin id="parse-feed" name="Feed Parse Plug-in" version="1.0.0"
	 provider-name="nutch.org">
    <runtime>
      <library name="parse-feed.jar">
        <export name="*" />
      </library>
      <library name="rome-0.9.jar" />
      <library name="jdom.jar" />
    </runtime>

    <requires>
      <import plugin="nutch-extensionpoints" />
    </requires>

    <extension id="com.treselle.parse.feed" name="Feed Parser"
      point="org.apache.nutch.parse.Parser">

      <implementation id="com.treselle.parse.feed.ParseFeed"
         class="com.treselle.parse.feed.ParseFeed">
         <parameter name="contentType" value="application/xml" />
          <parameter name="contentType" value="text/xml" />
		<parameter name="pathSuffix" value="rss" />
     </implementation>
    </extension>
</plugin>

<?xml version="1.0"?>

<plugin id="parse-feed" name="Feed Parse Plug-in" version="1.0.0"

provider-name="nutch.org">

</library>

</runtime>

</requires>

<extension id="com.treselle.parse.feed" name="Feed Parser"

point="org.apache.nutch.parse.Parser">

<implementation id="com.treselle.parse.feed.ParseFeed"

class="com.treselle.parse.feed.ParseFeed">

</implementation>

</extension>

</plugin>

This file needs to be located in
${nutch_home}/plugins/${plugin_name}/
This plugin.xml file instructs Nutch about parse-feed plugin.
The parser plug-in is mapped to two mime-types: application/xml and text/xml which is highlighted in bold.
Plugin id is very important in order to point out the respective plug-in.

build.xml
- Build the ant file with importing build-plugin.xml file which performs all the basic operations or targets of all plug-ins.
  
  build.xml
  
  <?xml version="1.0"?> <project name="parse-feed" default="jar-core"> <import file="../build-plugin.xml" /> </project>
  
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  <?xml version="1.0"?>
  
  <project name="parse-feed" default="jar-core">
  
  <import file="../build-plugin.xml" />
  
  </project>
- This build file imports the build-plugin.xml file which is highlighted in bold.

Create a Plug-in with Ant:

Plug-in Structure: The plug-in source files (ParseFeed.java), plugin.xml, and its build.xml files must be located as in below directory structure.

Build with ant : To build the parse-feed parser plug-in, add the lines given below in build.xml file which is located in ${nutch_home}/src/plugin

<target name="deploy"> <ant dir="parse-feed" target="deploy"/> </target>

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<target name="deploy">
<ant dir="parse-feed" target="deploy"/>
</target>
Create and copy the parse-feed plug-in
- Run the ant for ${nutch_home}/build.xml in command prompt, when all the files have been created, edited and saved in its locations, then compile and generate the parse-feed.jar.
  
  C:\Nutch\apache-nutch-1.1-bin> ant
  
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  C:\Nutch\apache-nutch-1.1-bin> ant
- This will build all the plugins in ${nutch_home}/build directory and create parse-feed plug-in with required files and jars in ${nutch_home}/build/plugins/parse-feed.
- Copy parse-feed folder (plugin) from ${nutch_home}/build/plugins directory and paste it in ${nutch_home}/plugins/parse-feed location.
- Parse-feed directory contains parse-feed’s plugin.xml, parse-feed.jar and its dependency jars which are located in lib folder of parse-feed parser directory.

Reconfigure with custom Parser:

parse-plugin.xml

By default, RSS mime-types: application/xml and text/xml are mapped with parse-tika pre-defined parser. So comment those mapping in parse-plugin.xml file.

Add application/xml and text/xml mime-type mapping with custom parser as shown below

<mimeType name="text/xml">
	<plugin id="parse-feed" />			
</mimeType>
<mimeType name="application/xml">
	<plugin id="parse-feed" />			
</mimeType>

</mimeType>

</mimeType>

Add alias mappings for parse-feed to the actual extension implementation ids described in parse-feed plugin’s plugin.xml file

<aliases> <alias name="parse-feed" extension-id="com.treselle.parse.feed.ParseFeed" /> </aliases>

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<aliases>
<alias name="parse-feed" extension-id="com.treselle.parse.feed.ParseFeed" />
</aliases>
To know more about parse-plugin.xml mapping, refer second series of the blog.

To crawl and index the content

If we want Nutch to use this parse-feed plugin, we have to add parse-feed id name to plugin.includes in conf/nutch-site.xml, which is given below in highlighted text. Remove parse-tika parser id if it is added in plugin.includes.

<property>
  	<name>plugin.includes</name>
<value>protocol-(http|ftp|httpclient)|urlfilter-regex|parse-feed|index-(basic|more)|scoring-opic|urlnormalizer-(pass|regex|basic)</value>
<description>Regular expression naming plug-in directory names to include. Any plug-in not matching   this expression is excluded. In any case you need at least include the nutch-extensionpoints plug-in. By  default Nutch includes crawling just HTML and plain text via HTTP, and basic indexing and search plugins. </description>
</property>

<name>plugin.includes</name>

<description>Regular expression naming plug-in directory names to include. Any plug-in not matching this expression is excluded. In any case you need at least include the nutch-extensionpoints plug-in. By default Nutch includes crawling just HTML and plain text via HTTP, and basic indexing and search plugins. </description>

</property>

Use the command given below in cygwin command prompt to crawl and index the content of a page

User@Pc-name /cygdrive/c/Nutch/apache-nutch-1.1-bin $ bin/nutch crawl seed.txt -dir crawler -depth 1 -topN 5

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User@Pc-name /cygdrive/c/Nutch/apache-nutch-1.1-bin
$ bin/nutch crawl seed.txt -dir crawler -depth 1 -topN 5
After the successful completion of crawling process using parse-feed parser plugin, run luke-all jar tool, and open crawler/index directory in that tool. We can see the details of the index such as number of documents, number of fields, field values for each document in luke-all application as given below:

Compare the result image given above with the result image in the first blog (Apache Nutch – A Web Crawler Framework).

We will be able to notice changes in the documents count.

This parse-feed adapter will add one document in each SyndEntry available in the RSS pages. This process helps us to get accurate content from each URL.

Conclusion

Apache Nutch plugin-in architecture enables us to extend with our own logic with Nutch, using interface like parse, index, and ScoringFilter.

The later series will focus on Apache Nutch integration with Hadoop MapReduce concept where we will see how Nutch executes all jobs.

References

Writing plug-in in Nutch:

http://wiki.apache.org/nutch/WritingPluginExample-1.2

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Piyush Golapkar

Im currently using apache-nutch 1.9.
i hav integrated it with elasticsearch 1.3.2 so the data gets indexed in elasticsearch.
now i need to write a plugin within nutch which will parse the data before idexing it.It should only take the data as per my requirements.can u plz help me with this..
Asmat Ali

Exactly the same question as Piyush asked for nutch 1.12 and Solr 6.3. Could you help any please?

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