Add getter for registered events

Before this change, the only way to access the registered types was
abusing the Java reflection to access private field
`EventTypes.typesByString`.

Allow instead to expose the registered types as public supported
method `EventTypes.getRegisteredEvents()`.

Release-Notes: Add public `EventTypes.getRegisteredEvents()`
Change-Id: I7b4369112e838b820e452a24b4ea0da80d7664d2

java/com/google/gerrit/server/events/EventTypes.java

diff --git a/java/com/google/gerrit/server/events/EventTypes.java b/java/com/google/gerrit/server/events/EventTypes.java
index 5498ec8..229ef86 100644
--- a/java/com/google/gerrit/server/events/EventTypes.java
+++ b/java/com/google/gerrit/server/events/EventTypes.java
@@ -14,6 +14,7 @@
 
 package com.google.gerrit.server.events;
 
+import com.google.common.collect.ImmutableMap;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -61,4 +62,15 @@
   public static Class<?> getClass(String type) {
     return typesByString.get(type);
   }
+
+  /**
+   * Get a copy of all currently registered events.
+   *
+   * <p>The key is the one given to the evenType parameter of the {@link #register} method.
+   *
+   * @return ImmutableMap of event types, Event classes.
+   */
+  public static Map<String, Class<?>> getRegisteredEvents() {
+    return ImmutableMap.copyOf(typesByString);
+  }
 }

javatests/com/google/gerrit/server/events/EventTypesTest.java

diff --git a/javatests/com/google/gerrit/server/events/EventTypesTest.java b/javatests/com/google/gerrit/server/events/EventTypesTest.java
index c822d6c..7e97f184 100644
--- a/javatests/com/google/gerrit/server/events/EventTypesTest.java
+++ b/javatests/com/google/gerrit/server/events/EventTypesTest.java
@@ -48,4 +48,16 @@
     Class<?> clazz = EventTypes.getClass("does-not-exist-event");
     assertThat(clazz).isNull();
   }
+
+  @Test
+  public void getRegisteredEventsGetsANewlyRegisteredEvent() {
+    EventTypes.register(TestEvent.TYPE, TestEvent.class);
+    assertThat(EventTypes.getRegisteredEvents()).containsEntry(TestEvent.TYPE, TestEvent.class);
+  }
+
+  @Test
+  public void getRegisteredEventsGetsTypeGivenAtRegistration() {
+    EventTypes.register("alternate-type", TestEvent.class);
+    assertThat(EventTypes.getRegisteredEvents()).containsEntry("alternate-type", TestEvent.class);
+  }
 }