现象，这个网站我总计能抽取将近500个URL，但实际只抽取了100条

解析：nutch默认从一个页面解析出的链接，只取前 100 个。 

<property>

  <name>db.max.outlinks.per.page</name>

  <value></value>

  <description>The maximum number of outlinks that we'll process for a page.

  If this value is nonnegative (>=), at most db.max.outlinks.per.page outlinks

  will be processed for a page; otherwise, all outlinks will be processed.

  </description>

</property>

将这个值改大一些 1000 .