Help debugging XML issues

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

Author: dscho

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

@@ -76,6 +76,9 @@ public class XML {
 	/** XPath evaluation mechanism. */
 	private final XPath xpath;
 
+	private final boolean debug =
+			"debug".equals(System.getProperty("scijava.log.level"));
+
 	/** Parses XML from the given file. */
 	public XML(final File file) throws ParserConfigurationException,
 		SAXException, IOException
@@ -123,6 +126,10 @@ public XML(final String path, final Document doc) {
 		// (because the XPathFactory will ask the context class loader to find the
 		// configured services, including the
 		// com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl).
+		if (debug) {
+			System.err.println(ClassUtils.getLocation(XPathFactory.class));
+		}
+
 		XPath xpath = null;
 		final Thread thread = Thread.currentThread();
 		final ClassLoader contextClassLoader = thread.getContextClassLoader();
@@ -135,10 +142,17 @@ public XML(final String path, final Document doc) {
 					// expressions (i.e. *not* throw NoSuchMethodErrors).
 					xpath.evaluate("//dummy", doc);
 				} catch (Throwable t) {
+					if (debug) {
+						System.err.println("There was a problem with " +
+							xpath.getClass() + " in " +
+							ClassUtils.getLocation(xpath.getClass()) + ":");
+						t.printStackTrace();
+					}
 					throw new Error(t);
 				}
 				break;
 			} catch (Error e) {
+				if (debug) e.printStackTrace();
 				loader = loader.getParent();
 				if (loader == null) throw e;
 				thread.setContextClassLoader(loader);