org.geotools.feature

Interface FeatureCollection<T extends FeatureType,F extends Feature>

All Known Subinterfaces:

RandomFeatureAccess, SimpleFeatureCollection, XmlFeatureCollection

All Known Implementing Classes:

AbstractFeatureCollection, AdaptorFeatureCollection, ArcSdeFeatureCollection, BaseFeatureCollection, BaseSimpleFeatureCollection, CollectionFeatureSource.SubCollection, CompositeFeatureCollection, ContentFeatureCollection, DataFeatureCollection, DecoratingFeatureCollection, DecoratingSimpleFeatureCollection, DefaultFeatureCollection, DefaultFeatureResults, EmptyFeatureCollection, FilteringFeatureCollection, FilteringSimpleFeatureCollection, ForceCoordinateSystemFeatureResults, GMLFeatureCollection, IndexedFeatureResults, ListFeatureCollection, MappingFeatureCollection, MaxFeaturesFeatureCollection, MaxSimpleFeatureCollection, MemoryFeatureCollection, PreGeneralizedFeatureCollection, ProcessingCollection, ReprojectFeatureResults, ReprojectingFeatureCollection, ReTypingFeatureCollection, SampleDataAccessFeatureCollection, SimpleProcessingCollection, SortedSimpleFeatureCollection, SpatialIndexFeatureCollection, SubFeatureCollection, SubFeatureList, TreeSetFeatureCollection, WFSContentComplexFeatureCollection

public interface FeatureCollection<T extends FeatureType,F extends Feature>

Collection of features, often handled as a result set.

Where possible FeatureCollection is method compatible with Collection.

SimpleFeatureCollection house rules:

• Each iterator is considered a live connection which must be closed (see example below)
• Features are not specifically ordered within the SimpleFeatureCollection
• Two Feature instances cannot exist with the same FeatureId

FeatureIterator close

FeatureCollection provides streaming access with the following restriction on the use of FeatureIterator: You must call FeatureIterator.close(). This allows FeatureCollection to clean up any operating system resources used to access information.

Example (safe) use:

 FeatureIterator iterator = featureCollection.features();
 try {
     while( iterator.hasNext() ){
          Feature feature = iterator.next();
          System.out.println( feature.getID() );
     }
 }
 finally {
     iterator.close();
 }
 

And in Java 7:

 try ( FeatureIterator iterator = featureCollection.features() ){
     while( iterator.hasNext() ){
          Feature feature = iterator.next();
          System.out.println( feature.getID() );
     }
 }
 

Handy Tip: Although many resource backed collections will choose to release resources at when the iterator has reached the end of its contents this is not something you should rely on.

FeatureCollection Implementation Tips

Auto close: Try and close up resources when you can detect that an Iterator is no longer in use.

Lazy Connect: FeatureCollection is used in two fashions, as a result set, where each iterator acts as a cursor over the content. Also as a predefined query which can be refined further. An example is using featureCollection.subCollection( Filter ) or featureCollection.sort( SortBy ) before listing features out of a FeatureCollection.

Author:

Ian Turton, CCG, Rob Hranac, VFNY, Ian Schneider, USDA-ARS, Jody Garnett, LISAsoft

See Also:

org.geotools.Feature

Method Summary

Modifier and Type	Method and Description
void	accepts(FeatureVisitor visitor, ProgressListener progress) Visit the contents of a feature collection.
boolean	contains(Object o)
boolean	containsAll(Collection<?> o)
FeatureIterator<F>	features() Obtain a FeatureIterator of the Features within this FeatureCollection.
ReferencedEnvelope	getBounds() Get the total bounds of this collection which is calculated by doing a union of the bounds of each feature inside of it
String	getID() ID used when serializing to GML
T	getSchema() The schema for the child feature members of this collection.
boolean	isEmpty() Returns true if this feature collection contains no features.
int	size() Please note this operation may be expensive when working with remote content.
FeatureCollection<T,F>	sort(SortBy order) Obtained sorted contents.
FeatureCollection<T,F>	subCollection(Filter filter) SimpleFeatureCollection "view" indicated by provided filter.
Object[]	toArray()
<O> O[]	toArray(O[] a)

Method Detail

features

FeatureIterator<F> features()

Obtain a FeatureIterator of the Features within this FeatureCollection.

The implementation of FeatureIterator must adhere to the rules of fail-fast concurrent modification. In addition (to allow for resource backed collections) the FeatureIterator.close() method must be called.

Example use:

 FeatureIterator iterator=collection.features();
 try {
     while( iterator.hasNext()  ){
          Feature feature = iterator.next();
          System.out.println( feature.getID() );
     }
 }
 finally {
     iterator.close();
 }
 

GML Note: The contents of this iterator are considered to be defined by featureMember tags (and/or the single allowed FeatureMembers tag). Please see getFeatureType for more details.

Returns:

A FeatureIterator.

getSchema

T getSchema()

The schema for the child feature members of this collection.

Represents the most general FeatureType in common to all the features in this collection.

• For a collection backed by a shapefiles (or database tables) the FeatureType returned by getSchema() will complete describe each and every child in the collection.
• For mixed content FeatureCollections you will need to check the FeatureType of each Feature as it is retrived from the collection
• The degenerate case returns the "_Feature" FeatureType, where the only thing known is that the contents are Features.

Returns:

FeatureType describing the "common" schema to all child features of this collection

getID

String getID()

ID used when serializing to GML

accepts

void accepts(FeatureVisitor visitor,
             ProgressListener progress)
      throws IOException

Visit the contents of a feature collection.

The order of traversal is dependent on the FeatureCollection implementation; some collections are able to make efficient use of an internal index in order to quickly visit features located in the same region.

Parameters:

visitor - Closure applied to each feature in turn.

progress - Used to report progress, may be used to interrupt the operation

Throws:

IOException

Since:

2.5

subCollection

FeatureCollection<T,F> subCollection(Filter filter)

SimpleFeatureCollection "view" indicated by provided filter.

The contents of the returned SimpleFeatureCollection are determined by applying the provider Filter to the entire contents of this FeatureCollection. The result is "live" and modifications will be shared.

This method is used cut down on the number of filter based methods required for a useful SimpleFeatureCollection construct. The FeatureCollections returned really should be considered as a temporary "view" used to control the range of a removeAll, or modify operation.

Example Use:

 collection.subCollection( filter ).clear();
 

The above recommended use is agreement with the Collections API precident of List.subList( start, end ).

The results of subCollection:

• are to be considered unordered
• may be an ordered FeatureList if requested when sortBy is indicated

Parameters:

filter -

Returns:

SimpleFeatureCollection identified as subset.

See Also:

FeatureList

sort

FeatureCollection<T,F> sort(SortBy order)

Obtained sorted contents.

This method may not be supported by all implementations, consider the use of FeatureSource.features( Query ).

Parameters:

order - Sort order

Returns:

FeatureCollection sorted in the indicated order

getBounds

ReferencedEnvelope getBounds()

Get the total bounds of this collection which is calculated by doing a union of the bounds of each feature inside of it

Returns:

An Envelope containing the total bounds of this collection.

contains

boolean contains(Object o)

See Also:

Collection.contains(Object)

containsAll

boolean containsAll(Collection<?> o)

See Also:

Collection.containsAll(Collection)

isEmpty

boolean isEmpty()

Returns true if this feature collection contains no features.

Returns:

true if this collection contains no features

size

int size()

Please note this operation may be expensive when working with remote content.

See Also:

Collection.size()

toArray

Object[] toArray()

See Also:

Collection.toArray()

toArray

<O> O[] toArray(O[] a)

See Also:

Collection.toArray(Object[])