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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
/*
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* SciJava Common shared library for SciJava software.
* %%
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* Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
* Institute of Molecular Cell Biology and Genetics, University of
* Konstanz, and KNIME GmbH.
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* modification, are permitted provided that the following conditions are met:
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* 1. Redistributions of source code must retain the above copyright notice,
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package org.scijava.service;
import java.util.List;
import org.scijava.object.SortedObjectIndex;
/**
* Data structure for tracking registered services.
*
* @author Curtis Rueden
*/
public class ServiceIndex extends SortedObjectIndex {
public ServiceIndex() {
super(Service.class);
}
// -- ServiceIndex methods --
/** Gets the first available service compatible with the given class. */
public S getService(final Class c) {
return getService(c, null, 0);
}
/**
* Gets the highest priority service compatible with class {@code c}, which is
* lower priority than the {@code ref} service.
*/
public S getNextService(final Class c,
final Class ref)
{
return getService(c, ref, 1);
}
/**
* Gets the lowest priority service compatible with class {@code c}, which is
* higher priority than the {@code ref} service.
*/
public S getPrevService(final Class c,
final Class ref)
{
return getService(c, ref, -1);
}
// -- Helper methods --
/**
* Gets the service compatible with the base class {@code c}, with the
* modified priority relative to the given reference service, or the highest
* priority service if no reference is given.
*
* @param c - Base class to find compatible services
* @param ref - Reference service class for priority comparisons. If null,
* highest priority service is returned.
* @param priorityMod - Relative priority value. If {@code ref} is non-null,
* this value is applied to the {@code ref} service's index in the
* list of compatible services to determine the returned service. For
* example, a value of +1 will return the next lowest priority
* service, and a value of -1 will return the next highest priority
* service - as the services are sorted from highest to lowest
* priority.
* @return Service matching the given criteria, or null if no applicable
* service.
*/
private S getService(final Class c,
final Class ref, final int priorityMod)
{
final List list = get(c);
if (list.isEmpty()) return null;
int index = 0;
if (ref != null) {
// find the ref class's index
for (; index < list.size() && !list.get(index).getClass().equals(ref); index++)
{}
// ref class wasn't on the list
if (index == list.size()) return null;
// Update the index for the desired relative priority
index += priorityMod;
}
// If the priorityMod took the index outside the list bounds, then there is
// no appropriate
// service to return.
if (index < 0 || index >= list.size()) return null;
@SuppressWarnings("unchecked")
final S service = (S) list.get(index);
return service;
}
}