Heritrix3.x自定义扩展Extractor

一、引言：

　　Heritrix3.x与Heritrix1.x版本差异比较大，全新配置模式的引入+扩展接口的变化，同时由于说明文档的匮乏，给Heritrix的开发者带来困惑，前面的文章已经就Heritrix的配置部署和运行做了说明，本文就Heritrix3.x版本就Extractor扩展做出实例说明。

二、配置说明

　　Heritrix3.x的WebUI发生了变化，不在是原来那种WebUI选择模式，而是变成了在线配置文件直接编辑模式。在这里自定义的Extractor要想加入Heritrix运行，首先需要修改配置文件，降自定义扩展的Extractor加入到Heritrix的Processor队列。完整配置文件如下所示：

　　2.1 配置文件

<!-- FETCH CHAIN --> 
 <!-- processors declared as named beans -->
 <bean id="preselector" class="org.archive.crawler.prefetch.Preselector">
 </bean>
 <bean id="preconditions" class="org.archive.crawler.prefetch.PreconditionEnforcer">
 </bean>
 <bean id="fetchDns" class="org.archive.modules.fetcher.FetchDNS">
 </bean>
 <bean id="fetchHttp" class="org.archive.modules.fetcher.FetchHTTP">
 </bean>
 <bean id="extractorHttp" class="org.archive.modules.extractor.ExtractorHTTP">
 </bean>
-------------------------------自定义Extractor------------------------------------
 <bean id="SohuNewsExtractor" class="my.SohuNewsExtractor">
 </bean>
---------------------------------------------------------------------------------
 <bean id="extractorHtml" class="org.archive.modules.extractor.ExtractorHTML">
 </bean>
 <bean id="extractorCss" class="org.archive.modules.extractor.ExtractorCSS">
 </bean> 
 <bean id="extractorJs" class="org.archive.modules.extractor.ExtractorJS">
 </bean>
 <bean id="extractorSwf" class="org.archive.modules.extractor.ExtractorSWF">
 </bean>    
 <!-- assembled into ordered FetchChain bean -->
 <bean id="fetchProcessors" class="org.archive.modules.FetchChain">
  <property name="processors">
   <list>
    <!-- recheck scope, if so enabled... -->
    <ref bean="preselector"/>
    <!-- ...then verify or trigger prerequisite URIs fetched, allow crawling... -->
    <ref bean="preconditions"/>
    <!-- ...fetch if DNS URI... -->
    <ref bean="fetchDns"/>
    <!-- ...fetch if HTTP URI... -->
    <ref bean="fetchHttp"/>
    <!-- ...extract oulinks from HTTP headers... -->
    <ref bean="extractorHttp"/>

----------------------------自定义Extractor----------------------------------------------
    <!-- ...extract oulinks from HTTP content... -->
    <ref bean="SohuNewsExtractor"/>
---------------------------------------------------------------------------------------
    <!-- ...extract oulinks from HTML content... -->
    <ref bean="extractorHtml"/>
    <!-- ...extract oulinks from CSS content... -->
    <ref bean="extractorCss"/>
    <!-- ...extract oulinks from Javascript content... -->
    <ref bean="extractorJs"/>
    <!-- ...extract oulinks from Flash content... -->
    <ref bean="extractorSwf"/>
   </list>
  </property>
 </bean>

　　2.2 添加Bean和配置调度列表

250  <bean id="extractorHttp" class="org.archive.modules.extractor.ExtractorHTTP">
251  </bean>
-------------------------------自定义Extractor------------------------------------
252  <bean id="SohuNewsExtractor" class="my.SohuNewsExtractor">
253  </bean>
---------------------------------------------------------------------------------
...
----------------------------自定义Extractor---------------------------------------
285     <!-- ...extract oulinks from HTTP content... -->
286     <ref bean="SohuNewsExtractor"/>
---------------------------------------------------------------------------------
配置完成以上部分，既可以实现自定义Extractor参与Processor任务处理的调度。

 三、程序说明

　　3.1 Extractor基类

　　Extractor基类发生了变化，新增了新的接口方法：

1     @Override
2     protected boolean shouldProcess(CrawlURI uri) {
3         // TODO Auto-generated method stub
4         return false;
5     }

　　如果不实现此方法，自定义扩展的Extractor的函数void extract(CrawlURI uri)将不会被调度。

　　3.2 构造函数

　　1.x版本的构造函数如下：　　

   public Extractor(String name, String description) {
        super(name, description);
        // TODO Auto-generated constructor stub
    }