App: add getBaseDirectory() API

Now you can ask an app for its base directory, as well as the name of
the system property which overrides that directory.

Author: ctrueden

src/main/java/org/scijava/app/AbstractApp.java

@@ -31,7 +31,10 @@
 
 package org.scijava.app;
 
+import java.io.File;
+
 import org.scijava.plugin.AbstractRichPlugin;
+import org.scijava.util.AppUtils;
 import org.scijava.util.Manifest;
 import org.scijava.util.POM;
 
@@ -95,4 +98,14 @@ public String getInfo(boolean mem) {
 		return sb.toString();
 	}
 
+	@Override
+	public String getSystemProperty() {
+		return getInfo().getName().toLowerCase() + ".dir";
+	}
+
+	@Override
+	public File getBaseDirectory() {
+		return AppUtils.getBaseDirectory(getSystemProperty(), getClass(), null);
+	}
+
 }

src/main/java/org/scijava/app/App.java

@@ -31,6 +31,8 @@
 
 package org.scijava.app;
 
+import java.io.File;
+
 import org.scijava.plugin.Plugin;
 import org.scijava.plugin.RichPlugin;
 import org.scijava.plugin.SingletonPlugin;
@@ -91,4 +93,17 @@ public interface App extends RichPlugin, SingletonPlugin {
 	 */
 	String getInfo(boolean mem);
 
+	/**
+	 * A system property which, if set, overrides the base directory of the
+	 * application.
+	 */
+	String getSystemProperty();
+
+	/**
+	 * Gets the application's root directory. If the application's system property
+	 * is set, it is used. Otherwise, we scan up the tree from this class for a
+	 * suitable directory.
+	 */
+	File getBaseDirectory();
+
 }