org.odpi.openmetadata.frameworks.connectors.properties

Class AssetPagingIterator

java.lang.Object

org.odpi.openmetadata.frameworks.connectors.properties.AssetPropertyElementBase

org.odpi.openmetadata.frameworks.connectors.properties.AssetPropertyBase

org.odpi.openmetadata.frameworks.connectors.properties.AssetPagingIterator

All Implemented Interfaces:

Serializable, Iterator<AssetPropertyBase>

public class AssetPagingIterator
extends AssetPropertyBase
implements Iterator<AssetPropertyBase>

PagingIterator supports an iterator over a list of objects that extend AssetPropertyBase. 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.

cachedElementList.size() is set to maxCacheSize() for all retrieves except for processing the last cache of elements. For example, if the totalElement is 25 and the maxCacheSize() is 10 then we would retrieve 3 caches - the first two would have 10 elements in them and the third will have 5 elements. In the first 2 retrieves, maxCacheSize and cachedElementList.size() are set to 10. In the last one, maxCacheSize==10 and cachedElementList.size()==5.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected List<AssetPropertyBase>	cachedElementList
protected int	cachedElementPointer
protected int	cachedElementStart
protected AssetPropertyIteratorBase	iterator
protected int	maxCacheSize
protected int	totalElementCount

Fields inherited from class org.odpi.openmetadata.frameworks.connectors.properties.AssetPropertyBase

parentAsset

Constructor Summary

Constructors

Constructor and Description
AssetPagingIterator(AssetDescriptor parentAsset, AssetPropertyIteratorBase iterator, AssetPagingIterator templateIterator) Copy/clone constructor.
AssetPagingIterator(AssetDescriptor parentAsset, AssetPropertyIteratorBase iterator, int totalElementCount, int maxCacheSize) Typical Constructor creates an iterator with the supplied list of comments.

Method Summary

Modifier and Type	Method and Description
int	getElementCount() Return the number of elements in the list.
boolean	hasNext() The iterator can only be used once to step through the elements.
AssetPropertyBase	next() Return the next element in the list
void	remove() Remove the current element in the iterator.
String	toString() Standard toString method.

Methods inherited from class org.odpi.openmetadata.frameworks.connectors.properties.AssetPropertyBase

equals, getParentAsset, getParentAssetName, getParentAssetTypeName, hashCode

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Iterator

forEachRemaining

Field Detail

maxCacheSize

protected int maxCacheSize

totalElementCount

protected int totalElementCount

cachedElementStart

protected int cachedElementStart

cachedElementList

protected List<AssetPropertyBase> cachedElementList

cachedElementPointer

protected int cachedElementPointer

iterator

protected AssetPropertyIteratorBase iterator

Constructor Detail

AssetPagingIterator

public AssetPagingIterator(AssetDescriptor parentAsset,
                           AssetPropertyIteratorBase iterator,
                           int totalElementCount,
                           int maxCacheSize)

Typical Constructor creates an iterator with the supplied list of comments.

Parameters:

parentAsset - descriptor of parent asset.

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.

AssetPagingIterator

public AssetPagingIterator(AssetDescriptor parentAsset,
                           AssetPropertyIteratorBase iterator,
                           AssetPagingIterator templateIterator)

Copy/clone constructor. Used to reset iterator element pointer to 0;

Parameters:

parentAsset - descriptor of parent asset

iterator - type-specific iterator that wraps this paging iterator.

templateIterator - template to copy; null to create an empty iterator

Method Detail

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<AssetPropertyBase>

Returns:

boolean indicating whether there are more elements.

next

public AssetPropertyBase next()

Return the next element in the list

Specified by:

next in interface Iterator<AssetPropertyBase>

Returns:

AssetPropertyBase next element.

Throws:

OCFRuntimeException - if there are no more elements in the list or there are problems retrieving elements from the property (metadata) server.

getElementCount

public int getElementCount()

Return the number of elements in the list.

Returns:

elementCount

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<AssetPropertyBase>

toString

public String toString()

Standard toString method.

Overrides:

toString in class Object

Returns:

print out of variables in a JSON-style