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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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/*
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 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2015 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
 * %%
 * 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.
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package org.scijava.convert;

import java.lang.reflect.Type;
import java.util.Collection;
import java.util.List;
import java.util.Set;

import org.scijava.object.ObjectService;
import org.scijava.plugin.HandlerPlugin;
import org.scijava.plugin.Plugin;

/**
 * Extensible conversion {@link Plugin} for converting between classes and
 * types.
 *
 * @see ConversionRequest
 * @author Mark Hiner
 */
public interface Converter extends HandlerPlugin {

	/**
	 * Checks whether a given {@ConversionRequest} can be
	 * processed, by converting the desired
	 * {@link ConversionRequest#sourceClass()} to its
	 * {@link ConversionRequest#destClass()} or
	 * {@link ConversionRequest#destType()}.
	 *
	 * @see #convert(ConversionRequest)
	 */
	boolean canConvert(ConversionRequest request);

	/**
	 * Checks whether the given object's type can be converted to the specified
	 * type.
	 * 
	 * Note that this does not necessarily entail that
	 * {@link #convert(Object, Type)} on that specific object will succeed. For
	 * example: {@code canConvert("5.1", int.class)} will return {@code true}
	 * because a {@link String} can in general be converted to an {@code int}, but
	 * calling {@code convert("5.1", int.class)} will throw a
	 * {@link NumberFormatException} when the conversion is actually attempted via
	 * the {@link Integer#Integer(String)} constructor.
	 * 
	 *
	 * @see #convert(Object, Type)
	 */
	boolean canConvert(Object src, Type dest);

	/**
	 * Checks whether the given object's type can be converted to the specified
	 * type.
	 * 
	 * Note that this does not necessarily entail that
	 * {@link #convert(Object, Class)} on that specific object will succeed. For
	 * example: {@code canConvert("5.1", int.class)} will return {@code true}
	 * because a {@link String} can in general be converted to an {@code int}, but
	 * calling {@code convert("5.1", int.class)} will throw a
	 * {@link NumberFormatException} when the conversion is actually attempted via
	 * the {@link Integer#Integer(String)} constructor.
	 * 
	 *
	 * @see #convert(Object, Class)
	 */
	boolean canConvert(Object src, Class dest);

	/**
	 * As {@link #convert(Object, Class)} but capable of creating and populating
	 * multi-element objects ({@link Collection}s and array types). If a single
	 * element type is provided, it will be converted the same as
	 * {@link #convert(Object, Class)}. If a multi-element type is detected, then
	 * the value parameter will be interpreted as potential collection of values.
	 * An appropriate container will be created, and the full set of values will
	 * be type converted and added.
	 * 
	 * NB: This method should be capable of creating any array type, but if a
	 * {@link Collection} interface or abstract class is provided we can only make
	 * a best guess as to what container type to instantiate. Defaults are
	 * provided for {@link Set} and {@link List} subclasses.
	 * 
	 *
	 * @param src The object to convert.
	 * @param dest Type to which the object should be converted.
	 */
	Object convert(Object src, Type dest);

	/**
	 * Converts the given object to an object of the specified type. The object is
	 * casted directly if possible, or else a new object is created using the
	 * destination type's public constructor that takes the original object as
	 * input (except when converting to {@link String}, which uses the
	 * {@link Object#toString()} method instead). In the case of primitive types,
	 * returns an object of the corresponding wrapped type. If the destination
	 * type does not have an appropriate constructor, returns null.
	 *
	 * @param  Type to which the object should be converted.
	 * @param src The object to convert.
	 * @param dest Type to which the object should be converted.
	 */
	 T convert(Object src, Class dest);

	/**
	 * Converts the given {@link ConversionRequest#sourceObject()} to the
	 * specified {@link ConversionRequest#destClass()} or
	 * {@link ConversionRequest#destType()}.
	 *
	 * @see #convert(Object, Class)
	 * @see #convert(Object, Type)
	 * @param request {@link ConversionRequest} to process.
	 * @return The conversion output
	 */
	Object convert(ConversionRequest request);

	/**
	 * Populates the given collection with objects which are known to exist, and
	 * which are usable as inputs for this converter.
	 * 
	 * That is: each such object added to the collection would return {@code true}
	 * if queried with {@code converter.canConvert(object)}, and hence would
	 * produce an output of type {@link #getOutputType()} if passed to
	 * {@code converter.convert(object)}.
	 * 
	 * 
	 * The means by which "known objects" are determined is implementation
	 * dependent, although the most typical use case is to query the
	 * {@link ObjectService} for known objects of type {@link #getInputType()},
	 * and return those. But other behaviors are possible, depending on the
	 * converter implementation.
	 * 
	 * 
	 * @param objects an initialized collection into which appropriate objects
	 *          will be inserted.
	 */
	void populateInputCandidates(Collection