Add a callback mechanism for script execution

The intended use case is for ScriptProcessor plugins to use it when they
need to do something every time (or deferred until the first time) a
script executes. Initially, this will be useful for dependency grabbing.

Author: ctrueden

src/main/java/org/scijava/script/ScriptInfo.java

@@ -40,6 +40,7 @@
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.text.SimpleDateFormat;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 
@@ -52,6 +53,7 @@
 import org.scijava.module.ModuleItem;
 import org.scijava.plugin.Parameter;
 import org.scijava.script.process.ParameterScriptProcessor;
+import org.scijava.script.process.ScriptCallback;
 import org.scijava.script.process.ScriptProcessorService;
 import org.scijava.util.DigestUtils;
 import org.scijava.util.FileUtils;
@@ -88,6 +90,9 @@ public class ScriptInfo extends AbstractModuleInfo implements Contextual {
 	/** Script language in which the script should be executed. */
 	private ScriptLanguage scriptLanguage;
 
+	/** Routines to be invoked prior to script execution. */
+	private ArrayList<ScriptCallback> callbacks;
+
 	/**
 	 * Creates a script metadata object which describes the given script file.
 	 * 
@@ -245,6 +250,18 @@ public void setReturnValueAppended(final boolean appendReturnValue) {
 		this.appendReturnValue = appendReturnValue;
 	}
 
+	/**
+	 * Gets the list of routines which should be invoked each time the script is
+	 * about to execute.
+	 * 
+	 * @return Reference to the mutable list of {@link Runnable} objects which the
+	 *         {@link ScriptModule} will run prior to executing the script itself.
+	 */
+	public List<ScriptCallback> callbacks() {
+		if (callbacks == null) callbacks = new ArrayList<>();
+		return callbacks;
+	}
+
 	// -- AbstractModuleInfo methods --
 
 	/**

src/main/java/org/scijava/script/ScriptModule.java

@@ -50,6 +50,7 @@
 import org.scijava.module.Module;
 import org.scijava.module.ModuleItem;
 import org.scijava.plugin.Parameter;
+import org.scijava.script.process.ScriptCallback;
 
 /**
  * A {@link Module} which executes a script.
@@ -149,9 +150,14 @@ public void run() {
 			engine.put(name, getInput(name));
 		}
 
-		// execute script!
 		returnValue = null;
 		try {
+			// invoke the callbacks
+			for (final ScriptCallback c : getInfo().callbacks()) {
+				c.invoke(this);
+			}
+
+			// execute script!
 			final Reader reader = getInfo().getReader();
 			if (reader == null) returnValue = engine.eval(new FileReader(path));
 			else returnValue = engine.eval(reader);

src/main/java/org/scijava/script/process/ScriptCallback.java

@@ -0,0 +1,52 @@
+/*
+ * #%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, 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.
+ * 
+ * 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.script.process;
+
+import javax.script.ScriptException;
+
+import org.scijava.script.ScriptModule;
+
+/**
+ * A routine which will be invoked just prior to script execution.
+ *
+ * @author Curtis Rueden
+ */
+public interface ScriptCallback {
+
+	/**
+	 * Invokes the callback routine.
+	 * 
+	 * @param module The {@link ScriptModule} instance which will
+	 *          execute the script.
+	 */
+	void invoke(final ScriptModule module) throws ScriptException;
+}