Package org.odpi.openmetadata.frameworks.connectors.properties

Class PagingIterator

java.lang.Object
org.odpi.openmetadata.frameworks.connectors.properties.beans.PropertyBase
org.odpi.openmetadata.frameworks.connectors.properties.PagingIterator
All Implemented Interfaces:
Iterator<ElementBase>
public class PagingIterator extends PropertyBase implements Iterator<ElementBase>

PagingIterator supports an iterator over a list of objects that extend ElementBase. Callers can use it to step through the list just once. If they want to parse the list again, they could use the copy/clone constructor to create a new iterator.

PagingIterator provides paging support to enable the list in the iterator to be much bigger than can be stored in memory. It maintains pointers for the full list, and a potentially smaller cached list that is used to batch up elements being retrieved from the property (metadata) server.

Thus is combines the ability to process very large lists whilst minimising the chatter with the property server. The class uses a number of pointers and counts. Imagine a list of 4000 columns in a table. We can not retrieve all 4000 columns on one call. So we retrieve subsets over a number of REST calls as the caller walks through the full list.

  • maxCacheSize is the maximum elements we can retrieve in one call
  • cachedElementList.size() is how many elements we have in memory at this time.

  • Field Details

    • maxCacheSize

      protected int maxCacheSize
      Maximum that can be returned on each retrieve

    • cachedElementStart

      protected int cachedElementStart
      StartFrom used on calls to the repository

    • cachedElementList

      protected List<ElementBase> cachedElementList
      Elements retrieved from the repository

    • cachedElementPointer

      protected int cachedElementPointer
      Pointer in the cached list to the next item to return.

    • iterator

      protected PropertyIteratorBase iterator
      Implementation that retrieves values from the repository.

    • log

      protected static final org.slf4j.Logger log
      Logging destination.

  • Constructor Details

    • PagingIterator

      public PagingIterator(PropertyIteratorBase iterator, int maxCacheSize)
      Typical Constructor creates an iterator with the supplied list of comments.
      Parameters:
      iterator - type-specific iterator that wraps this paging iterator.
      maxCacheSize - maximum number of elements that should be retrieved from the property server and cached in the element list at any one time. If a number less than one is supplied, 1 is used.

    • PagingIterator

      public PagingIterator(PropertyIteratorBase iterator, PagingIterator templateIterator)
      Copy/clone constructor. Used to reset iterator element pointer to 0;
      Parameters:
      iterator - type-specific iterator that wraps this paging iterator.
      templateIterator - template to copy; null to create an empty iterator

  • Method Details

    • hasNext

      public boolean hasNext()
      The iterator can only be used once to step through the elements. This method returns a boolean to indicate if it has got to the end of the list yet.
      Specified by:
      hasNext in interface Iterator<ElementBase>
      Returns:
      boolean indicating whether there are more elements.

    • next

      public ElementBase next()
      Return the next element in the list
      Specified by:
      next in interface Iterator<ElementBase>
      Returns:
      ElementBase next element.
      Throws:
      OMFRuntimeException - if there are no more elements in the list or there are problems retrieving elements from the property (metadata) server.

    • remove

      public void remove()
      Remove the current element in the iterator. This call is not supported and results in an exception
      Specified by:
      remove in interface Iterator<ElementBase>

    • toString

      public String toString()
      Standard toString method.
      Overrides:
      toString in class Object
      Returns:
      print out of variables in a JSON-style