Class PagingIterator
java.lang.Object
org.odpi.openmetadata.frameworks.connectors.properties.beans.PropertyBase
org.odpi.openmetadata.frameworks.connectors.properties.PagingIterator
- All Implemented Interfaces:
Serializable
,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.
- totalElement is 4000 - ie how many elements there are in total.
- maxCacheSize is the maximum elements we can retrieve in one call
- cachedElementList.size() is how many elements we have in memory at this time.
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected List<ElementBase>
protected int
protected int
protected PropertyIteratorBase
protected static final org.slf4j.Logger
protected int
protected int
Fields inherited from class org.odpi.openmetadata.frameworks.connectors.properties.beans.PropertyBase
CURRENT_AUDIT_HEADER_VERSION
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Constructor Summary
ConstructorsConstructorDescriptionPagingIterator
(PropertyIteratorBase iterator, int totalElementCount, int maxCacheSize) Typical Constructor creates an iterator with the supplied list of comments.PagingIterator
(PropertyIteratorBase iterator, PagingIterator templateIterator) Copy/clone constructor. -
Method Summary
Modifier and TypeMethodDescriptionint
Return the number of elements in the list.boolean
hasNext()
The iterator can only be used once to step through the elements.next()
Return the next element in the listvoid
remove()
Remove the current element in the iterator.toString()
Standard toString method.Methods inherited from class org.odpi.openmetadata.frameworks.connectors.properties.beans.PropertyBase
equals, getHeaderVersion, hashCode, setHeaderVersion
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Methods inherited from interface java.util.Iterator
forEachRemaining
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Field Details
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maxCacheSize
protected int maxCacheSize -
totalElementCount
protected int totalElementCount -
cachedElementStart
protected int cachedElementStart -
cachedElementList
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cachedElementPointer
protected int cachedElementPointer -
iterator
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log
protected static final org.slf4j.Logger log
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Constructor Details
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PagingIterator
Typical Constructor creates an iterator with the supplied list of comments.- Parameters:
iterator
- type-specific iterator that wraps this paging iterator.totalElementCount
- the total number of elements to process. A negative value is converted to 0.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.
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PagingIterator
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
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Method Details
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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 interfaceIterator<ElementBase>
- Returns:
- boolean indicating whether there are more elements.
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next
Return the next element in the list- Specified by:
next
in interfaceIterator<ElementBase>
- Returns:
- ElementBase next element.
- Throws:
OCFRuntimeException
- if there are no more elements in the list or there are problems retrieving elements from the property (metadata) server.
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getElementCount
public int getElementCount()Return the number of elements in the list.- Returns:
- elementCount
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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 interfaceIterator<ElementBase>
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toString
Standard toString method.
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