Merge pull request #123 from scijava/convertable-inputs

Converters can now populate candidate input lists when their output types are requested.

Author: hinerm

src/main/java/org/scijava/convert/AbstractConvertService.java

@@ -43,7 +43,7 @@
  * @author Mark Hiner
  */
 public abstract class AbstractConvertService extends
-	AbstractHandlerService<ConversionRequest, Converter> implements
+	AbstractHandlerService<ConversionRequest, Converter<?, ?>> implements
 	ConvertService
 {
 
@@ -58,13 +58,13 @@ public Object convert(Object src, Type dest) {
 	public <T> T convert(Object src, Class<T> dest) {
 		// NB: repeated code with convert(ConversionRequest), because the
 		// handler's convert method respects the T provided
-		Converter handler = getHandler(src, dest);
+		Converter<?, ?> handler = getHandler(src, dest);
 		return handler == null ? null : handler.convert(src, dest);
 	}
 
 	@Override
 	public Object convert(ConversionRequest request) {
-		Converter handler = getHandler(request);
+		Converter<?, ?> handler = getHandler(request);
 		return handler == null ? null : handler.convert(request);
 	}
 

src/main/java/org/scijava/convert/AbstractConverter.java

@@ -31,22 +31,30 @@
 
 package org.scijava.convert;
 
+import java.util.Collection;
+
 import org.scijava.plugin.AbstractHandlerPlugin;
 
 /**
- * Abstract superclass for {@link Converter} plugins. Performs
- * appropriate dispatching of {@link #canConvert(ConversionRequest)} and
+ * Abstract superclass for {@link Converter} plugins. Performs appropriate
+ * dispatching of {@link #canConvert(ConversionRequest)} and
  * {@link #convert(ConversionRequest)} calls based on the actual state of the
  * given {@link ConversionRequest}.
  * <p>
  * Note that the {@link #supports(ConversionRequest)} method is overridden as
  * well, to delegate to the appropriate {@link #canConvert}.
  * </p>
+ * <p>
+ * NB: by default, the {@link #populateInputCandidates(Collection)} method has a
+ * dummy implementation. Effectively, this is opt-in behavior. If a converter
+ * implementation would like to suggest candidates for conversion, this method
+ * can be overridden.
+ * </p>
  *
  * @author Mark Hiner
  */
-public abstract class AbstractConverter extends
-	AbstractHandlerPlugin<ConversionRequest> implements Converter
+public abstract class AbstractConverter<I, O> extends
+	AbstractHandlerPlugin<ConversionRequest> implements Converter<I, O>
 {
 
 	// -- ConversionHandler methods --
@@ -74,6 +82,11 @@ public Object convert(final ConversionRequest request) {
 		return null;
 	}
 
+	@Override
+	public void populateInputCandidates(final Collection<Object> objects) {
+		// No-op
+	}
+
 	// -- Typed methods --
 
 	@Override

src/main/java/org/scijava/convert/ConvertService.java

@@ -32,6 +32,7 @@
 package org.scijava.convert;
 
 import java.lang.reflect.Type;
+import java.util.Collection;
 
 import org.scijava.plugin.HandlerService;
 
@@ -45,7 +46,7 @@
  * @author Mark Hiner
  */
 public interface ConvertService extends
-	HandlerService<ConversionRequest, Converter>
+	HandlerService<ConversionRequest, Converter<?, ?>>
 {
 	/**
 	 * @see Converter#convert(Object, Type)
@@ -65,22 +66,22 @@ public interface ConvertService extends
 	/**
 	 * @see #getHandler(ConversionRequest)
 	 */
-	Converter getHandler(Object src, Class<?> dest);
+	Converter<?, ?> getHandler(Object src, Class<?> dest);
 
 	/**
 	 * @see #getHandler(ConversionRequest)
 	 */
-	Converter getHandler(Class<?> src, Class<?> dest);
+	Converter<?, ?> getHandler(Class<?> src, Class<?> dest);
 
 	/**
 	 * @see #getHandler(ConversionRequest)
 	 */
-	Converter getHandler(Object src, Type dest);
+	Converter<?, ?> getHandler(Object src, Type dest);
 
 	/**
 	 * @see #getHandler(ConversionRequest)
 	 */
-	Converter getHandler(Class<?> src, Type dest);
+	Converter<?, ?> getHandler(Class<?> src, Type dest);
 
 	/**
 	 * @see #supports(ConversionRequest)
@@ -101,4 +102,6 @@ public interface ConvertService extends
 	 * @see #supports(ConversionRequest)
 	 */
 	boolean supports(Class<?> src, Type dest);
+
+	Collection<Object> getCompatibleInputs(Class<?> dest);
 }

src/main/java/org/scijava/convert/Converter.java

@@ -36,6 +36,7 @@
 import java.util.List;
 import java.util.Set;
 
+import org.scijava.object.ObjectService;
 import org.scijava.plugin.HandlerPlugin;
 import org.scijava.plugin.Plugin;
 
@@ -46,7 +47,8 @@
  * @see ConversionRequest
  * @author Mark Hiner
  */
-public interface Converter extends HandlerPlugin<ConversionRequest> {
+public interface Converter<I, O> extends HandlerPlugin<ConversionRequest>
+{
 
 	/**
 	 * Checks whether a given {@ConversionRequest} can be
@@ -155,4 +157,36 @@ public interface Converter extends HandlerPlugin<ConversionRequest> {
 	 * @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.
+	 * <p>
+	 * 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)}.
+	 * </p>
+	 * <p>
+	 * 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.
+	 * </p>
+	 * 
+	 * @param objects an initialized collection into which appropriate objects
+	 *          will be inserted.
+	 */
+	void populateInputCandidates(Collection<Object> objects);
+
+	/**
+	 * @return The base {@code Class} this {@code Converter} produces as output.
+	 */
+	Class<O> getOutputType();
+
+	/**
+	 * @return The base {@code Class} this {@code Converter} accepts as input.
+	 */
+	Class<I> getInputType();
 }

src/main/java/org/scijava/convert/DefaultConvertService.java

@@ -32,6 +32,10 @@
 package org.scijava.convert;
 
 import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.Set;
 
 import org.scijava.plugin.Plugin;
 import org.scijava.service.Service;
@@ -45,9 +49,10 @@
 public class DefaultConvertService extends AbstractConvertService
 {
 
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	@Override
-	public Class<Converter> getPluginType() {
-		return Converter.class;
+	public Class<Converter<?, ?>> getPluginType() {
+		return (Class)Converter.class;
 	}
 
 	@Override
@@ -58,22 +63,22 @@ public Class<ConversionRequest> getType() {
 	// -- ConversionService methods --
 
 	@Override
-	public Converter getHandler(final Object src, final Class<?> dest) {
+	public Converter<?, ?> getHandler(final Object src, final Class<?> dest) {
 		return getHandler(new ConversionRequest(src, dest));
 	}
 
 	@Override
-	public Converter getHandler(final Class<?> src, final Class<?> dest) {
+	public Converter<?, ?> getHandler(final Class<?> src, final Class<?> dest) {
 		return getHandler(new ConversionRequest(src, dest));
 	}
 
 	@Override
-	public Converter getHandler(final Object src, final Type dest) {
+	public Converter<?, ?> getHandler(final Object src, final Type dest) {
 		return getHandler(new ConversionRequest(src, dest));
 	}
 
 	@Override
-	public Converter getHandler(final Class<?> src, final Type dest) {
+	public Converter<?, ?> getHandler(final Class<?> src, final Type dest) {
 		return getHandler(new ConversionRequest(src, dest));
 	}
 
@@ -96,4 +101,17 @@ public boolean supports(final Object src, final Type dest) {
 	public boolean supports(final Class<?> src, final Type dest) {
 		return supports(new ConversionRequest(src, dest));
 	}
+
+	@Override
+	public Collection<Object> getCompatibleInputs(Class<?> dest) {
+		Set<Object> objects = new LinkedHashSet<Object>();
+
+		for (final Converter<?, ?> c : getInstances()) {
+			if (dest.isAssignableFrom(c.getOutputType())) {
+				c.populateInputCandidates(objects);
+			}
+		}
+
+		return new ArrayList<Object>(objects);
+	}
 }

src/main/java/org/scijava/convert/DefaultConverter.java

@@ -55,7 +55,7 @@
  * @author Mark Hiner
  */
 @Plugin(type = Converter.class)
-public class DefaultConverter extends AbstractConverter {
+public class DefaultConverter extends AbstractConverter<Object, Object> {
 
 	// -- ConversionHandler methods --
 
@@ -265,6 +265,16 @@ public <T> T convert(final Object src, final Class<T> dest) {
 		}
 	}
 
+	@Override
+	public Class<Object> getOutputType() {
+		return Object.class;
+	}
+
+	@Override
+	public Class<Object> getInputType() {
+		return Object.class;
+	}
+
 	// -- Helper methods --
 
 	private Constructor<?> getConstructor(final Class<?> type,

src/main/java/org/scijava/util/ConversionUtils.java

@@ -51,7 +51,7 @@ public class ConversionUtils {
 
 	private static ConvertService convertService;
 
-	private static Converter converterNoContext;
+	private static Converter<?, ?> converterNoContext;
 
 	private static double servicePriority = 0.0;
 
@@ -195,7 +195,7 @@ public static void setDelegateService(final ConvertService convertService,
 	 */
 	@Deprecated
 	public static Object convert(final Object src, final Type dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? null : handler.convert(src, dest));
 	}
 
@@ -205,7 +205,7 @@ public static Object convert(final Object src, final Type dest) {
 	 */
 	@Deprecated
 	public static <T> T convert(final Object src, final Class<T> dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? null : handler.convert(src, dest));
 	}
 
@@ -215,7 +215,7 @@ public static <T> T convert(final Object src, final Class<T> dest) {
 	 */
 	@Deprecated
 	public static boolean canConvert(final Class<?> src, final Type dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? false : handler.canConvert(src, dest));
 	}
 
@@ -225,7 +225,7 @@ public static boolean canConvert(final Class<?> src, final Type dest) {
 	 */
 	@Deprecated
 	public static boolean canConvert(final Class<?> src, final Class<?> dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? false : handler.canConvert(src, dest));
 	}
 
@@ -235,7 +235,7 @@ public static boolean canConvert(final Class<?> src, final Class<?> dest) {
 	 */
 	@Deprecated
 	public static boolean canConvert(final Object src, final Type dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? false : handler.canConvert(src, dest));
 	}
 
@@ -245,7 +245,7 @@ public static boolean canConvert(final Object src, final Type dest) {
 	 */
 	@Deprecated
 	public static boolean canConvert(final Object src, final Class<?> dest) {
-		final Converter handler = handler(new ConversionRequest(src, dest));
+		final Converter<?, ?> handler = handler(new ConversionRequest(src, dest));
 		return (handler == null ? false : handler.canConvert(src, dest));
 	}
 
@@ -270,7 +270,7 @@ public static Class<?> getComponentClass(final Type type) {
 	 *
 	 * @return The {@link Converter} to use for handling the given request.
 	 */
-	private static Converter handler(final ConversionRequest data) {
+	private static Converter<?, ?> handler(final ConversionRequest data) {
 		if (convertService != null) return convertService.getHandler(data);
 
 		if (converterNoContext == null) converterNoContext = new DefaultConverter();

src/main/java/org/scijava/widget/AbstractInputHarvester.java

@@ -35,6 +35,7 @@
 import java.util.List;
 
 import org.scijava.AbstractContextual;
+import org.scijava.convert.ConvertService;
 import org.scijava.module.Module;
 import org.scijava.module.ModuleCanceledException;
 import org.scijava.module.ModuleException;
@@ -63,6 +64,9 @@ public abstract class AbstractInputHarvester<P, W> extends AbstractContextual
 	@Parameter
 	private ObjectService objectService;
 
+	@Parameter
+	private ConvertService convertService;
+
 	// -- InputHarvester methods --
 
 	@Override
@@ -142,9 +146,14 @@ private <T> WidgetModel addInput(final InputPanel<P, W> inputPanel,
 		return null;
 	}
 
-	/** Asks the object service for valid choices */
-	private <T> List<T> getObjects(final Class<T> type) {
-		return objectService.getObjects(type);
+	/** Asks the object service and convert service for valid choices */
+	@SuppressWarnings("unchecked")
+	private List<?> getObjects(final Class<?> type) {
+		@SuppressWarnings("rawtypes")
+		List compatibleInputs =
+			new ArrayList(convertService.getCompatibleInputs(type));
+		compatibleInputs.addAll(objectService.getObjects(type));
+		return compatibleInputs;
 	}
 
 }