Only write META-INF/json/ if annotations were found

Originally, we wanted to run the EclipseHelper only for a limited set of
situations, using the test whether the first class path element of the
current class loader is a directory as an indicator that we're running
in Eclipse. We also wanted to use the time stamp of META-INF/json/ as an
indicator whether we need to index the annotations or not.

However, it turns out that we probably need to run in more situations,
e.g. because the directories in question might be first indexed during a
run inside a LegacyEnvironment.

So let's just punt and run the EclipseHelper in more situations, but
avoid to write META-INF/json/ unless we really have anything to write.

This addresses #33.

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

Author: dscho

src/main/java/org/scijava/annotations/AbstractIndexWriter.java

@@ -60,6 +60,10 @@ public abstract class AbstractIndexWriter {
 	private final Map<String, Map<String, Object>> map =
 		new TreeMap<String, Map<String, Object>>();
 
+	protected synchronized boolean foundAnnotations() {
+		return !map.isEmpty();
+	}
+
 	protected synchronized void add(final Map<String, Object> annotationValues,
 		final String annotationName, final String className)
 	{

src/main/java/org/scijava/annotations/EclipseHelper.java

@@ -212,16 +212,17 @@ private void index(File directory, ClassLoader loader) {
 				+ ", up-to-date: " + upToDate(directory));
 			return;
 		}
-		System.err.println("[ECLIPSE HELPER] Indexing annotations...");
+		final File jsonDirectory = new File(directory, Index.INDEX_PREFIX);
 		try {
 			discoverAnnotations(directory, "", loader);
+			if (!jsonDirectory.exists() && !foundAnnotations()) return;
+			System.err.println("[ECLIPSE HELPER] Indexing annotations...");
 			write(directory);
 		}
 		catch (IOException e) {
 			e.printStackTrace();
 		}
 		// update the timestamp of META-INF/json/
-		final File jsonDirectory = new File(directory, Index.INDEX_PREFIX);
 		if (jsonDirectory.isDirectory()) {
 			jsonDirectory.setLastModified(System.currentTimeMillis());
 		}