PrefService: Provide an API for Iterables

The most generic way to provide a bunch of Strings to persist is by
passing an Iterable<String> for writing and handling an Iterable<String>
when reading.

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

Author: dscho

src/main/java/org/scijava/prefs/DefaultPrefService.java

@@ -378,6 +378,28 @@ public List<String> getList(final Class<?> prefClass) {
 		return getList(preferences);
 	}
 
+	@Override
+	public Iterable<String> getIterable(final String key) {
+		return getIterable((Class<?>) null, key);
+	}
+
+	@Override
+	public Iterable<String> getIterable(final Class<?> prefClass, final String key) {
+		final Preferences preferences = prefs(prefClass);
+		return getIterable(preferences.node(key));
+	}
+
+	@Override
+	public void putIterable(final Iterable<String> iterable, final String key) {
+		putIterable((Class<?>) null, iterable, key);
+	}
+
+	@Override
+	public void putIterable(final Class<?> prefClass, final Iterable<String> iterable, final String key) {
+		final Preferences preferences = prefs(prefClass);
+		putIterable(preferences.node(key), iterable);
+	}
+
 	// -- Helper methods --
 
 	private void clear(final Preferences preferences, final String key) {
@@ -460,6 +482,60 @@ private List<String> getList(final Preferences preferences) {
 		return list;
 	}
 
+	private void putIterable(final Preferences preferences,
+		final Iterable<String> iterable)
+	{
+		if (preferences == null) {
+			throw new IllegalArgumentException("Preferences not set.");
+		}
+		int index = 0;
+		for (final String value : iterable) {
+			preferences.put("" + index++, value == null ? null : value.toString());
+		}
+	}
+
+	private Iterable<String> getIterable(final Preferences preferences)
+	{
+		if (preferences == null) {
+			throw new IllegalArgumentException("Preferences not set.");
+		}
+		return new Iterable<String>() {
+			@Override
+			public Iterator<String> iterator() {
+				return new Iterator<String>() {
+					private String value;
+					private int index;
+					{
+						findNext();
+					}
+
+					@Override
+					public String next() {
+						final String result = value;
+						findNext();
+						return result;
+					}
+
+					@Override
+					public boolean hasNext() {
+						return value != null;
+					}
+
+					@Override
+					public void remove() {
+						throw new UnsupportedOperationException();
+					}
+
+					private void findNext() {
+						if (index < 0) return;
+						value = preferences.get("" + index, null);
+						index = value == null ? -1 : index + 1;
+					}
+				};
+			}
+		};
+	}
+
 	private Preferences prefs(final Class<?> c) {
 		return Preferences.userNodeForPackage(c == null ? PrefService.class : c);
 	}

src/main/java/org/scijava/prefs/PrefService.java

@@ -194,4 +194,24 @@ public interface PrefService extends SciJavaService {
 	 * prefs.
 	 */
 	List<String> getList(Class<?> prefClass);
+
+	/**
+	 * Puts an iterable into the preferences.
+	 */
+	void putIterable(Iterable<String> iterable, String key);
+
+	/**
+	 * Puts an iterable into the preferences.
+	 */
+	void putIterable(Class<?> prefClass, Iterable<String> iterable, String key);
+
+	/**
+	 * Gets an iterable from the preferences.
+	 */
+	Iterable<String> getIterable(String key);
+
+	/**
+	 * Gets an iterable from the preferences.
+	 */
+	Iterable<String> getIterable(Class<?> prefClass, String key);
 }