Allow running inside Maven unit tests

When Maven's surefire plugin runs unit tests, the URLClassLoader does
actually not list the URLs corresponding to the dependencies. Instead,
surefire tries to be clever and hides those dependencies inside a
single, empty .jar file's manifest's Class-Path: entry.

We are not dumb, so surefire loses: we get the URLs anyway. Hah! Take
this, surefire! *shakes-fist*

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/main/java/org/scijava/plugins/scripting/java/JavaEngine.java

@@ -43,10 +43,14 @@
 import java.io.Reader;
 import java.io.StringReader;
 import java.io.Writer;
+import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.jar.JarFile;
+import java.util.jar.Manifest;
+import java.util.jar.Attributes.Name;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -463,15 +467,49 @@ private static List<Coordinate> getAllDependencies(final BuildEnvironment env) {
 				for (final URL url : ((URLClassLoader)loader).getURLs()) {
 					if (url.getProtocol().equals("file")) {
 						final File file = new File(url.getPath());
-						final String artifactId = fakeArtifactId(env, file.getName());
-						Coordinate dependency = new Coordinate(DEFAULT_GROUP_ID, artifactId, "1.0.0");
-						env.fakePOM(file, dependency);
-						result.add(dependency);
+						if (url.toString().matches(".*/target/surefire/surefirebooter[0-9]*\\.jar")) {
+							getSurefireBooterURLs(file, url, env, result);
+							continue;
+						}
+						result.add(fakeDependency(env, file));
 					}
 				}
 			}
 		}
 		return result;
 	}
 
+	private static Coordinate fakeDependency(final BuildEnvironment env, final File file) {
+		final String artifactId = fakeArtifactId(env, file.getName());
+		Coordinate dependency = new Coordinate(DEFAULT_GROUP_ID, artifactId, "1.0.0");
+		env.fakePOM(file, dependency);
+		return dependency;
+	}
+
+	private static void getSurefireBooterURLs(final File file, final URL baseURL,
+		final BuildEnvironment env, final List<Coordinate> result)
+	{
+		try {
+			final JarFile jar = new JarFile(file);
+			Manifest manifest = jar.getManifest();
+			if (manifest != null) {
+				final String classPath =
+					manifest.getMainAttributes().getValue(Name.CLASS_PATH);
+				if (classPath != null) {
+					for (final String element : classPath.split(" +"))
+						try {
+							final File dependency = new File(new URL(baseURL, element).getPath());
+							result.add(fakeDependency(env, dependency));
+						}
+						catch (MalformedURLException e) {
+							e.printStackTrace();
+						}
+				}
+			}
+		}
+		catch (final IOException e) {
+			e.printStackTrace();
+		}
+	}
+
 }