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Package org.geotools.factory

Utility classes which enable dynamic binding to factory implementations at runtime.

See: Description

Package org.geotools.factory Description

Utility classes which enable dynamic binding to factory implementations at runtime.

Because Geotools core API consists almost exclusively of interfaces (including GeoAPI), factories play a role in how developers use the API. Although the interfaces that are declared in GeoAPI are implemented in various Geotools packages you should not use those classes directly. Instead you should use factories.

J2SE's ServiceRegistry provides a general way (even if it is defined in a javax.imageio subpackage) to instantiate and manage factories (also called providers). Each factory implementation should be declared in META-INF/services directory, usually bundled in every JAR file. For example if a JAR file provides one or more DatumFactory implementations, then it must provide the following file:

META-INF/services/org.opengis.referencing.datum.DatumFactory

with a content similar to the one below:

com.mycompany.MyDatumFactory1
com.mycompany.MyDatumFactory2
com.mycompany.MyDatumFactory3

The ordering is initially unspecified. Users can set an ordering explicitly themselves, or implementations can do that automatically on registration. The AbstractFactory class provides a simple way to setup ordering on registration on the basis of a priority number.

If a user wants a specific implementation, he can iterates through registered ones and pickup the desired implementation himself. An alternative is to bundle the criterions in a map of hints and lets the registry selects an implementation accordingly. This later functionality is not provided by the standard ServiceRegistry, but is provided by Geotools's FactoryRegistry extension. This class extends the service registry API with the following functionalities:

Note that the hints, if provided, don't need to apply directly to the requested factory category. They may apply indirectly through some dependency. A typical example is a request for any GeometryFactory instance, providing that this instance uses a particular CoordinateSequenceFactory implementation.

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