Add convenient way to build input-only commands

The idea is to build up the inputs with code dynamically in Java, run
the command (which does nothing when executed) to exploit the module
preprocessing chain, and then harvest the final input values.

In this way, the user can be prompted for inputs dynamically from Java
code, roughly similar to the ij.gui.GenericDialog class of ImageJ 1.x.

Author: ctrueden

src/main/java/org/scijava/command/DynamicCommand.java

@@ -63,7 +63,7 @@ public abstract class DynamicCommand extends DefaultMutableModule implements
 	private CommandService commandService;
 
 	@Parameter
-	private PluginService pluginService;
+	protected PluginService pluginService;
 
 	@Parameter
 	protected ModuleService moduleService;

src/main/java/org/scijava/command/Inputs.java

@@ -0,0 +1,105 @@
+/*
+ * #%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
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.command;
+
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ExecutionException;
+
+import org.scijava.Context;
+import org.scijava.module.process.PreprocessorPlugin;
+
+/**
+ * A way to build a dynamic set of inputs, whose values are then harvested by
+ * the preprocessing framework.
+ * <p>
+ * The {@link #run()} method of this command does nothing. If you want something
+ * custom to happen during execution, use a normal {@link Command} instead:
+ * either implement {@link Command directly}, or extend {@link ContextCommand}
+ * or {@link DynamicCommand}.
+ * </p>
+ * <p>
+ * Here is are some examples of usage:
+ * </p>
+ *
+ * <pre>
+ * {@code
+ * // Single input, no configuration.
+ * Inputs inputs = new Inputs(context);
+ * inputs.addInput("sigma", Double.class);
+ * Double sigma = (Double) inputs.harvest().get("sigma");
+ *
+ * // Two inputs, no configuration.
+ * Inputs inputs = new Inputs(context);
+ * inputs.addInput("name", String.class);
+ * inputs.addInput("age", Integer.class);
+ * Map<String, Object> values = inputs.harvest();
+ * String name = (String) values.get("name");
+ * Integer age = (Integer) values.get("age");
+ *
+ * // Inputs with configuration.
+ * Inputs inputs = new Inputs(context);
+ * MutableModuleItem<String> wordInput = inputs.addInput("word", String.class);
+ * wordInput.setLabel("Favorite word");
+ * wordInput.setChoices(Arrays.asList("quick", "brown", "fox"));
+ * wordInput.setDefaultValue("fox");
+ * MutableModuleItem<Double> opacityInput = inputs.addInput("opacity", Double.class);
+ * opacityInput.setMinimumValue(0.0);
+ * opacityInput.setMaximumValue(1.0);
+ * opacityInput.setDefaultValue(0.5);
+ * opacityInput.setWidgetStyle(NumberWidget.SCROLL_BAR_STYLE);
+ * inputs.harvest();
+ * String word = wordInput.getValue(inputs);
+ * Double opacity = opacityInput.getValue(inputs);
+ * }
+ * </pre>
+ *
+ * @author Curtis Rueden
+ */
+public final class Inputs extends DynamicCommand {
+
+	public Inputs(final Context context) {
+		context.inject(this);
+	}
+
+	public Map<String, Object> harvest() {
+		try {
+			final List<PreprocessorPlugin> pre = //
+				pluginService.createInstancesOfType(PreprocessorPlugin.class);
+			return moduleService.run(this, true, pre, null).get().getInputs();
+		}
+		catch (final InterruptedException | ExecutionException exc) {
+			throw new RuntimeException(exc);
+		}
+	}
+}