Allow user to enumerate supported content types (#350)

Signed-off-by: Dave Syer <[email protected]>

Author: Dave Syer

core/src/main/java/io/cloudevents/core/provider/EventFormatProvider.java

@@ -17,70 +17,85 @@
 
 package io.cloudevents.core.provider;
 
-import io.cloudevents.core.format.EventFormat;
-import io.cloudevents.lang.Nullable;
-
-import javax.annotation.ParametersAreNonnullByDefault;
 import java.util.HashMap;
 import java.util.ServiceLoader;
+import java.util.Set;
+import java.util.TreeSet;
 import java.util.stream.StreamSupport;
 
+import javax.annotation.ParametersAreNonnullByDefault;
+
+import io.cloudevents.core.format.EventFormat;
+import io.cloudevents.lang.Nullable;
+
 /**
- * Singleton holding the discovered {@link EventFormat} implementations through {@link ServiceLoader}.
+ * Singleton holding the discovered {@link EventFormat} implementations through
+ * {@link ServiceLoader}.
  * <p>
- * You can resolve an event format using {@code EventFormatProvider.getInstance().resolveFormat(contentType)}.
+ * You can resolve an event format using
+ * {@code EventFormatProvider.getInstance().resolveFormat(contentType)}.
  * <p>
- * You can programmatically add a new {@link EventFormat} implementation using {@link #registerFormat(EventFormat)}.
+ * You can programmatically add a new {@link EventFormat} implementation using
+ * {@link #registerFormat(EventFormat)}.
  */
 @ParametersAreNonnullByDefault
 public final class EventFormatProvider {
 
-    private static class SingletonContainer {
-        private final static EventFormatProvider INSTANCE = new EventFormatProvider();
-    }
+	private static class SingletonContainer {
+		private final static EventFormatProvider INSTANCE = new EventFormatProvider();
+	}
+
+	/**
+	 * @return instance of {@link EventFormatProvider}
+	 */
+	public static EventFormatProvider getInstance() {
+		return EventFormatProvider.SingletonContainer.INSTANCE;
+	}
 
-    /**
-     * @return instance of {@link EventFormatProvider}
-     */
-    public static EventFormatProvider getInstance() {
-        return EventFormatProvider.SingletonContainer.INSTANCE;
-    }
+	private final HashMap<String, EventFormat> formats;
 
-    private final HashMap<String, EventFormat> formats;
+	private EventFormatProvider() {
+		this.formats = new HashMap<>();
 
-    private EventFormatProvider() {
-        this.formats = new HashMap<>();
+		StreamSupport.stream(ServiceLoader.load(EventFormat.class).spliterator(), false)
+				.forEach(this::registerFormat);
+	}
 
-        StreamSupport.stream(
-            ServiceLoader.load(EventFormat.class).spliterator(),
-            false
-        ).forEach(this::registerFormat);
-    }
+	/**
+	 * Register a new {@link EventFormat} programmatically.
+	 *
+	 * @param format the new format to register
+	 */
+	public void registerFormat(EventFormat format) {
+		for (String k : format.deserializableContentTypes()) {
+			this.formats.put(k, format);
+		}
+	}
 
-    /**
-     * Register a new {@link EventFormat} programmatically.
-     *
-     * @param format the new format to register
-     */
-    public void registerFormat(EventFormat format) {
-        for (String k : format.deserializableContentTypes()) {
-            this.formats.put(k, format);
-        }
-    }
+	/**
+	 * Enumerate the supported content types.
+	 * 
+	 * @return an alphabetically sorted list of content types
+	 */
+	public Set<String> getContentTypes() {
+		Set<String> types = new TreeSet<>();
+		types.addAll(this.formats.keySet());
+		return types;
+	}
 
-    /**
-     * Resolve an event format starting from the content type.
-     *
-     * @param contentType the content type to resolve the event format
-     * @return null if no format was found for the provided content type
-     */
-    @Nullable
-    public EventFormat resolveFormat(String contentType) {
-        int i = contentType.indexOf(';');
-        if (i != -1) {
-            contentType = contentType.substring(0, i);
-        }
-        return this.formats.get(contentType);
-    }
+	/**
+	 * Resolve an event format starting from the content type.
+	 *
+	 * @param contentType the content type to resolve the event format
+	 * @return null if no format was found for the provided content type
+	 */
+	@Nullable
+	public EventFormat resolveFormat(String contentType) {
+		int i = contentType.indexOf(';');
+		if (i != -1) {
+			contentType = contentType.substring(0, i);
+		}
+		return this.formats.get(contentType);
+	}
 
 }

core/src/test/java/io/cloudevents/core/provider/EventFormatProviderTest.java

@@ -36,4 +36,9 @@ void resolveCSVWithParams() {
             .isInstanceOf(CSVFormat.class);
     }
 
+    @Test
+    void listTypes() {
+        assertThat(EventFormatProvider.getInstance().getContentTypes()).hasSize(1);
+    }
+
 }