Package com.norconex.collector.http.delay.impl

Class AbstractDelayResolver

java.lang.Object
com.norconex.collector.http.delay.impl.AbstractDelayResolver
All Implemented Interfaces:
IDelayResolver, IXMLConfigurable
Direct Known Subclasses:
GenericDelayResolver, ReferenceDelayResolver
public abstract class AbstractDelayResolver extends Object implements IDelayResolver, IXMLConfigurable

Base implementation for creating voluntary delays between URL downloads. This base class offers a few ways the actual delay value can be defined (in order):

  1. Takes the delay specify by a robots.txt file. Only applicable if robots.txt files and its robots crawl delays are not ignored.
  2. Takes an explicitly specified delay, as per implementing class.
  3. Use the specified default delay or 3 seconds, if none is specified.

One of these following scope dictates how the delay is applied, listed in order from the best behaved to the least.

  • crawler: the delay is applied between each URL download within a crawler instance, regardless how many threads are defined within that crawler, or whether URLs are from the same site or not. This is the default scope.
  • site: the delay is applied between each URL download from the same site within a crawler instance, regardless how many threads are defined. A site is defined by a URL protocol and its domain (e.g. http://example.com).
  • thread: the delay is applied between each URL download from any given thread. The more threads you have the less of an impact the delay will have.

XML configuration usage:

The following should be shared across concrete implementations (which can add more configurable attributes and tags). 


<delay
    class="(implementing class)"
    default="(milliseconds)"
    ignoreRobotsCrawlDelay="[false|true]"
    scope="[crawler|site|thread]"/>
Since:
2.5.0
Author:
Pascal Essiembre

  • Field Details

  • Constructor Details

    • AbstractDelayResolver

      public AbstractDelayResolver()

  • Method Details

    • delay

      public void delay(RobotsTxt robotsTxt, String url)
      Description copied from interface: IDelayResolver
      Delay crawling activities (if applicable).
      Specified by:
      delay in interface IDelayResolver
      Parameters:
      robotsTxt - robots.txt instance (if applicable)
      url - the URL being crawled

    • getDefaultDelay

      public long getDefaultDelay()
      Gets the default delay in milliseconds.
      Returns:
      default delay

    • setDefaultDelay

      public void setDefaultDelay(long defaultDelay)
      Sets the default delay in milliseconds.
      Parameters:
      defaultDelay - default deleay

    • isIgnoreRobotsCrawlDelay

      public boolean isIgnoreRobotsCrawlDelay()
      Gets whether to ignore crawl delays specified in a site robots.txt file. Not applicable when robots.txt are ignored.
      Returns:
      true if ignoring robots.txt crawl delay

    • setIgnoreRobotsCrawlDelay

      public void setIgnoreRobotsCrawlDelay(boolean ignoreRobotsCrawlDelay)
      Sets whether to ignore crawl delays specified in a site robots.txt file. Not applicable when robots.txt are ignored.
      Parameters:
      ignoreRobotsCrawlDelay - true if ignoring robots.txt crawl delay

    • getScope

      public String getScope()
      Gets the delay scope.
      Returns:
      delay scope

    • setScope

      public void setScope(String scope)
      Sets the delay scope.
      Parameters:
      scope - one of "crawler", "site", or "thread".

    • resolveExplicitDelay

      protected abstract long resolveExplicitDelay(String url)
      Resolves explicitly specified delay, in milliseconds. This method is only invoked when there are no delays from robots.txt. If the implementing class does not have a delay resolution, -1 is returned (the default delay will be used).
      Parameters:
      url - URL for which to resolve delay
      Returns:
      delay in millisecond, or -1

    • loadFromXML

      public final void loadFromXML(XML xml)
      Specified by:
      loadFromXML in interface IXMLConfigurable

    • loadDelaysFromXML

      protected void loadDelaysFromXML(XML xml)
      Loads explicit configuration of delays form XML. Implementors should override this method if they wish to add extra configurable elements. Default implementation does nothing.
      Parameters:
      xml - configuration

    • saveToXML

      public final void saveToXML(XML xml)
      Specified by:
      saveToXML in interface IXMLConfigurable

    • saveDelaysToXML

      protected void saveDelaysToXML(XML xml)
      Saves explicit configuration of delays to XML. Implementors should override this method if they wish to add extra configurable elements. Default implementation does nothing.
      Parameters:
      xml - XML

    • equals

      public boolean equals(Object other)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object