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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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/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2017 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, Max Planck
 * Institute of Molecular Cell Biology and Genetics, University of
 * Konstanz, and KNIME GmbH.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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package org.scijava.plugin;

import java.util.List;

/**
 * A service for managing {@link HandlerPlugin}s of a particular type.
 * 
 * For any given data object, the service is capable of determining the most
 * appropriate handler by sequentially querying each handler plugin on its list
 * (via {@link HandlerPlugin#supports}).
 * 
 * 
 * @author Curtis Rueden
 * @param  Base data type handled by the handlers.
 * @param  Plugin type of the handlers.
 * @see HandlerPlugin
 */
public interface HandlerService> extends
	SingletonService, TypedService
{

	/**
	 * Gets the most appropriate handler for the given data object, or null if no
	 * handler supports it.
	 */
	default PT getHandler(final DT data) {
		for (final PT handler : getInstances()) {
			if (handler.supports(data)) return handler;
		}
		return null;
	}

	// -- SingletonService methods --

	/**
	 * Gets the list of handlers. There will be one singleton instance for each
	 * available handler plugin.
	 */
	@Override
	List getInstances();

	// -- Typed methods --

	/** Gets whether the given data object is supported. */
	@Override
	default boolean supports(final DT data) {
		return getHandler(data) != null;
	}
}