plugin(插件)為nutch提供了一些功能強(qiáng)大的部件,舉個(gè)例子, HtmlParser 就是使用比較普遍的用來(lái)分析nutch抓取的html文件的插件。
?????? 為什么nutch要使用這樣的plugin系統(tǒng)?
???? ??? 有三個(gè)原因:
1:可擴(kuò)展性
?????? 通過(guò)plugin,nutch允許任何人擴(kuò)展它的功能,而我們要做的只是對(duì)給定的接口做簡(jiǎn)單的實(shí)現(xiàn),舉個(gè)例子:MSWordParser這個(gè)插件是用來(lái)分析wordwendang的,它就是一個(gè)對(duì)parser這個(gè)接口的實(shí)現(xiàn)
2:靈活性
????? 因?yàn)槊總€(gè)人都可以根據(jù)自己的需求而寫(xiě)自己的plugin,這樣plugin就會(huì)有一個(gè)很強(qiáng)大的資源庫(kù)。這樣對(duì)與應(yīng)用nutch程序員來(lái)說(shuō),他可以在自己的搜索引擎上安裝符合自己需求的插件,而這些插件就在nutch的plugins中。這對(duì)于正在應(yīng)用nutch的開(kāi)發(fā)者來(lái)說(shuō)應(yīng)該是一個(gè)巨大的福音,因?yàn)槟阌辛烁嗟年P(guān)于內(nèi)容抽取的算法來(lái)選擇,很容易就增加了pdf的分析。
3:可維護(hù)性
每個(gè)開(kāi)發(fā)者只要關(guān)注自己的問(wèn)題。對(duì)于內(nèi)核的開(kāi)發(fā)者在為引擎內(nèi)核擴(kuò)展的同時(shí),為a plug添加一個(gè)描述它的接口就可以了。一個(gè)plugin的開(kāi)發(fā)者只要關(guān)注這個(gè)plugin所要實(shí)現(xiàn)的功能,而不需要知道整個(gè)系統(tǒng)是怎么工作的。它們僅僅需要知道的是plugin和plug之間交換的數(shù)據(jù)類(lèi)型。這使得內(nèi)核更加簡(jiǎn)單,更容易維護(hù)。
?????? plugin相關(guān)--什么是plugin,plugin的工作原理
nutch的 plugin系統(tǒng)是基于Eclipse 2.x中對(duì)插件的使用。plugins對(duì)nutch的工作是很重要的。所有的nutch中的parsing(分析),indexing(索引),searching(查詢)都是通過(guò)不同的plugins來(lái)實(shí)現(xiàn)的。
在編寫(xiě)一個(gè)plugin的時(shí)候,你要為一個(gè)擴(kuò)展點(diǎn)添加一個(gè)或者更多的擴(kuò)展項(xiàng)。這些Nutch的擴(kuò)展點(diǎn)是Nutch在一個(gè)plugin中已經(jīng)定義好了,這個(gè)plugin是 NutchExtensionPoints (所有的擴(kuò)展點(diǎn)都會(huì)在NutchExtensionPoints plugin.xml 這個(gè)文件中列出)。每一個(gè)擴(kuò)展點(diǎn)都定義了一個(gè)接口,這個(gè)接口在擴(kuò)展時(shí)必須被實(shí)現(xiàn)。這些擴(kuò)展點(diǎn)如下:
??? onlineClusterer-為在線的查詢結(jié)果提供分組算法的擴(kuò)展點(diǎn)的接口
??? indexingFiltering-允許為所索引中的Field添加元數(shù)據(jù)。所有的實(shí)現(xiàn)了這個(gè)接口plugin會(huì)在分析的過(guò)程中順序的逐個(gè)運(yùn)行
??? Ontology
??? Parser
??? 實(shí)現(xiàn)這個(gè)接口的parser讀取所抓取的document,摘取將被索引的數(shù)據(jù)。如果你要在nutch中為擴(kuò)展分析一個(gè)新內(nèi)容類(lèi)型或者從現(xiàn)有的可分析的內(nèi)容摘取更多的數(shù)據(jù)。
HtmlParseFilter
為html parser添加額外的元數(shù)據(jù)
protocol
實(shí)現(xiàn)Protocol的plugin可以使得nutch能使用更多的網(wǎng)絡(luò)協(xié)議(ftp,http)去抓取數(shù)據(jù)
QueryFilter
為查詢轉(zhuǎn)換的擴(kuò)展點(diǎn)
URLFileter
實(shí)現(xiàn)這個(gè)擴(kuò)展點(diǎn)的plugin會(huì)對(duì)nutch要抓取的網(wǎng)頁(yè)的urls進(jìn)行限制,RegexURLFilter提供了通過(guò)正則表達(dá)式來(lái)對(duì)Nutch爬行網(wǎng)頁(yè)的urls的控制。如果你對(duì)urls還有更加復(fù)雜的控制要求,你可以編寫(xiě)對(duì)這個(gè)urlfilter的實(shí)現(xiàn)
NutchAnalyser
為許多語(yǔ)言特定的分析器提供了擴(kuò)展點(diǎn)
源文件
在plugin的源文件目錄中你會(huì)找到以下的文件
plugin.xml???? 向nutch描述這個(gè)plugin的信息
build.xml????? 告訴ant怎樣編譯這個(gè)plugin
plugin的源碼
在Nutch使用plugin
如果要在Nutch使用一個(gè)給定的plugin,你需要對(duì)conf/nutch-site.xml進(jìn)行編輯并且把plugin的名字添加到plugin.includes中
Nutch plugin系統(tǒng)中的一些概念
?
編寫(xiě)一個(gè)pluginExample
??????? 思考編寫(xiě)這樣的一個(gè)plugin:我們想為一個(gè)給定的search term推薦一些與之相關(guān)的網(wǎng)頁(yè)。舉個(gè)例子,假設(shè)我們正在索引網(wǎng)頁(yè),當(dāng)我們注意到有一組網(wǎng)頁(yè)的內(nèi)容是關(guān)于plugin的,所以我們想如果當(dāng)某人查詢plugin的時(shí)候,我們可以推薦他到pluginCentral這個(gè)網(wǎng)頁(yè),但是同時(shí),也要返回在一般邏輯中的查詢結(jié)果所有的hits。所以我們將查詢結(jié)果分成了推薦結(jié)果和一般查詢結(jié)果。
??????? 你瀏覽你的網(wǎng)頁(yè)然后把一個(gè)meta-tags加入網(wǎng)頁(yè)中,它會(huì)告訴plugin這個(gè)網(wǎng)頁(yè)是應(yīng)該被推薦的。這個(gè)tags應(yīng)該像這樣
<meta name="recommended" content="plugins" />
為了達(dá)到目標(biāo)我們需要寫(xiě)一個(gè)plugin,這個(gè)plugin擴(kuò)展3個(gè)不同的擴(kuò)展點(diǎn),它們是:
HTMLParser:從meta-tags得到推薦的terms
IndexingFilter:增加一個(gè)推薦Field在索引中。
QueryFilter:增加對(duì)索引中新Field的查詢能力
要建立的文件
首先在plugin的目錄中新建一個(gè)目錄來(lái)盛放自己的的plugin,整個(gè)plugin我們?nèi)∶麨閞ecommended,然后在這個(gè)目錄里面
依次建立以下文件:
a plugin.xml,這個(gè)文件用來(lái)向Nutch描述我們新建的plugin
a build.xml這個(gè)文件告訴編譯器應(yīng)該怎樣build這個(gè)plugin
plugin的源代碼則保存在/src/java/org/apache/nutch/parse/recommended/[這里]
Plugin.xml
你所建立的plugin.xml應(yīng)該這樣:??
<?xml version="1.0" encoding="UTF-8"?> <plugin id="recommended" name="Recommended Parser/Filter" version="0.0.1" provider-name="nutch.org"> <runtime> <!-- As defined in build.xml this plugin will end up bundled as recommended.jar --> <library name="recommended.jar"> <export name="*"/> </library> </runtime> <!-- The RecommendedParser extends the HtmlParseFilter to grab the contents of any recommended meta tags --> <extension id="org.apache.nutch.parse.recommended.recommendedfilter" name="Recommended Parser" point="org.apache.nutch.parse.HtmlParseFilter"> <implementation id="RecommendedParser" class="org.apache.nutch.parse.recommended.RecommendedParser"/> </extension> <!-- TheRecommendedIndexer extends the IndexingFilter in order to add the contents of the recommended meta tags (as found by the RecommendedParser) to the lucene index. --> <extension id="org.apache.nutch.parse.recommended.recommendedindexer" name="Recommended identifier filter" point="org.apache.nutch.indexer.IndexingFilter"> <implementation id="RecommendedIndexer" class="org.apache.nutch.parse.recommended.RecommendedIndexer"/> </extension> <!-- The RecommendedQueryFilter gets called when you perform a search. It runs a search for the user's query against the recommended fields.??? In order to get add this to the list of filters that gets run by default, you have to use "fields=DEFAULT". --> <extension id="org.apache.nutch.parse.recommended.recommendedSearcher" name="Recommended Search Query Filter" point="org.apache.nutch.searcher.QueryFilter"> <implementation id="RecommendedQueryFilter" class="org.apache.nutch.parse.recommended.RecommendedQueryFilter" fields="DEFAULT"/> </extension> </plugin>
Build.xml
<?xml version="1.0"?> <project name="recommended" default="jar"> <import file="../build-plugin.xml"/> </project>
???
?
The HTML Parser Extension
這是對(duì)HtmlParserExtension這個(gè)擴(kuò)展點(diǎn)的實(shí)現(xiàn),它的作用是抓取那些標(biāo)meta-tags的內(nèi)容,這樣把它們加入正在分析的document中。.
package org.apache.nutch.parse.recommended; // JDK imports import java.util.Enumeration; import java.util.Properties; import java.util.logging.Logger; // Nutch imports import org.apache.nutch.parse.HTMLMetaTags; import org.apache.nutch.parse.Parse; import org.apache.nutch.parse.HtmlParseFilter; import org.apache.nutch.protocol.Content; import org.apache.nutch.util.LogFormatter; public class RecommendedParser implements HtmlParseFilter { private static final Logger LOG = LogFormatter .getLogger(RecommendedParser.class.getName()); /** The Recommended meta data attribute name */ public static final String META_RECOMMENDED_NAME="Recommended"; /** * 在html文件中尋找有沒(méi)有標(biāo)有meta-tags的內(nèi)容???? */ public Parse filter(Content content, Parse parse, HTMLMetaTags metaTags, DocumentFragment doc) { // Trying to find the document's recommended term String recommendation = null; Properties generalMetaTags = metaTags.getGeneralTags(); for (Enumeration tagNames = generalMetaTags.propertyNames(); tagNames.hasMoreElements(); ) { if (tagNames.nextElement().equals("recommended")) { recommendation = generalMetaTags.getProperty("recommended"); LOG.info("Found a Recommendation for " + recommendation); } } if (recommendation == null) { LOG.info("No Recommendataion"); } else { LOG.info("Adding Recommendation for " + recommendation); parse.getData().getMetadata().put(META_RECOMMENDED_NAME, recommendation); } return parse; } }
The Indexer Extension
這是對(duì)索引點(diǎn)的擴(kuò)展,如果查找到帶有meta-tags的內(nèi)容,就把它命名”recommended’的field中,然后加入document建立索引??
package org.apache.nutch.parse.recommended; // JDK import import java.util.logging.Logger; // Nutch imports import org.apache.nutch.util.LogFormatter; import org.apache.nutch.fetcher.FetcherOutput; import org.apache.nutch.indexer.IndexingFilter; import org.apache.nutch.indexer.IndexingException; import org.apache.nutch.parse.Parse; // Lucene imports import org.apache.lucene.document.Field; import org.apache.lucene.document.Document; public class RecommendedIndexer implements IndexingFilter { public static final Logger LOG = LogFormatter.getLogger(RecommendedIndexer.class.getName()); public RecommendedIndexer() { } public Document filter(Document doc, Parse parse, FetcherOutput fo) throws IndexingException { String recommendation = parse.getData().get("Recommended"); if (recommendation != null) { Field recommendedField = Field.Text("recommended", recommendation); recommendedField.setBoost(5.0f); doc.add(recommendedField); LOG.info("Added " + recommendation + " to the recommended Field"); } return doc; } }
The QueryFilter
當(dāng)用戶進(jìn)行查找操作的時(shí)候,QueryFilter就會(huì)被調(diào)用,而且對(duì)于recommeded中的boost值會(huì)影響查詢結(jié)果的排序。
package org.apache.nutch.parse.recommended; import org.apache.nutch.searcher.FieldQueryFilter; import java.util.logging.Logger; import org.apache.nutch.util.LogFormatter; public class RecommendedQueryFilter extends FieldQueryFilter { private static final Logger LOG = LogFormatter .getLogger(RecommendedParser.class.getName()); public RecommendedQueryFilter() { super("recommended", 5f); LOG.info("Added a recommended query"); } }
讓Nutch可以使用你的plugin
為了讓Nutch使用你的plugin,你需要對(duì)conf/nuthc-site.xml這個(gè)文件進(jìn)行編輯,把
以下的代碼加入
<property> <name>plugin.includes</name> <value>nutch-extensionpoints|protocol-http|urlfilter-regex|parse-(text|html)|index-basic|query-(basic|site|url)|recommended
</value> <description>Regular expression naming plugin directory 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>
使用Ant對(duì)你的plugin進(jìn)行編譯
在之前我們要編輯一下src/plugin/build.xml 這個(gè)文件,這是對(duì)編譯和部署做一些設(shè)置
你會(huì)看到有很多如下形式的行
<ant dir="[plugin-name]" target="deploy" />
在</target>前添加一新行
??? <ant dir="reccomended" target="deploy" />
Running ‘a(chǎn)nt’ in the root of your checkout directory should get everything compiled and jared up. The next time you run a crawl your parser and index filter should get used.
You’ll need to run ‘a(chǎn)nt war’ to compile a new ROOT.war file. Once you’ve deployed that, your query filter should get used when searches are performed.
plugins和class加載到nutch的問(wèn)題集合
對(duì)plugin開(kāi)發(fā)者來(lái)說(shuō)最棒的事情就是自由了,可以不去理會(huì)別的plugin的開(kāi)發(fā)者在做什么,可以自由的使用第三方的jar庫(kù)。
nutch是怎樣解決類(lèi)加載這個(gè)問(wèn)題的?
Nutch使用了一個(gè)非常容易的方法,每一個(gè)plugin都有一個(gè)屬于自己的類(lèi)加載器,這個(gè)class-loader在plugin啟動(dòng)以前將會(huì)被初始化
???????? 寫(xiě)plugin-by stefan
nutch 0.7中的plugins
如果你要在nutch中應(yīng)用這些插件,你只需要編輯conf/nutch-site.xml,把你所要用的plugin的名字加入plugin.includes的列表中
- clustering-carrot2 ?– Online Search Results Clustering using Carrot2’s Lingo component.
- creativecommons ?– Support for crawling and searching Creative-Commons licensed content.
- index-basic ?– Adds url, content and anchor fields to the index.
- index-more ?– Adds date, content-length, contentType, primaryType and subtype fields to the index.
- languageidentifier ?– Adds a lang field to the index and allows you to query against it.
- ontology ?– Helps refine queries based on owl files.
- parse-ext ?– A wrapper that invokes external command to do real parsing job.
- parse-html ?– Parses HTML documents
- parse-js ?– Parses JavaScript
- parse-mp3 ?– Parses MP3s
- parse-msword ?– Parses MS Word documents
- parse-pdf ?– Parses PDFs
- parse-rss ?– Parses RSS feeds
- parse-rtf ?– Parses RTF files
- parse-text ?– Parses text documents
- protocol-file ?– Retreives documents from the filesystem
- protocol-ftp ?– Retreives documents through ftp
- protocol-http ?– Retreives documents through http
- protocol-httpclient ?– Retreives documents through http and https
- query-basic ?– Runs queries against content, url and anchor fields
- query-more ?– Runs queries against date, content-length, contentType, primaryType and subType fields.
- query-site ?– Runs queries against site field
- query-url ?– Runs queries against url field.
- urlfilter-prefix
- urlfilter-regex
Additional Plugins in Dev Branch (0.8)
- analysis-de
- analysis-fr
- lib-commons-httpclient
- lib-http
- lib-jakarta-poi
- lib-log4j
- lib-lucene-analyzers
- lib-nekohtml
- lib-parsems
- parse-msexcel ?– Parses MS Excel documents
- parse-mspowerpoint ?– Parses MS Powerpoint documents
- parse-oo ?– Parses Open Office and Star Office documents (Extentsions: ODT, OTT, ODH, ODM, ODS, OTS, ODP, OTP, SXW, STW, SXC, STC, SXI, STI)
- parse-swf ?– Parses Flash SWF files
-
microformats-reltag
?– Adds?
?rel-tag ?fields to the index and runs queries against them.
- parse-zip
?原文地址: http://blog.csdn.net/geogre_jsj/article/details/5726646
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