Issue #87 Added the ability to check if a given flag is known to the client.

src/main/java/com/launchdarkly/client/LDClient.java

@@ -308,6 +308,24 @@ public JsonElement jsonVariation(String featureKey, LDUser user, JsonElement def
     return value;
   }
 
+  @Override
+  public boolean isFlagKnown(String featureKey) {
+    if (!initialized()) {
+      logger.warn("Evaluation called before Client has been initialized for feature flag " + featureKey + "; returning unknown");
+      return false;
+    }
+
+    try {
+      if (config.featureStore.get(featureKey) != null) {
+        return true;
+      }
+    } catch (Exception e) {
+      logger.error("Encountered exception in LaunchDarkly client", e);
+    }
+
+    return false;
+  }
+
   private JsonElement evaluate(String featureKey, LDUser user, JsonElement defaultValue, VariationType expectedType) {
     if (user == null || user.getKey() == null) {
       logger.warn("Null user or null user key when evaluating flag: " + featureKey + "; returning default value");

src/main/java/com/launchdarkly/client/LDClientInterface.java

@@ -30,6 +30,8 @@ public interface LDClientInterface extends Closeable {
 
   JsonElement jsonVariation(String featureKey, LDUser user, JsonElement defaultValue);
 
+  boolean isFlagKnown(String featureKey);
+
   @Override
   void close() throws IOException;
 

src/test/java/com/launchdarkly/client/LDClientTest.java

@@ -272,6 +272,49 @@ public void testTestFeatureStoreJsonVariationArray() throws Exception {
     verifyAll();
   }
 
+  @Test
+  public void testIsFlagKnown() throws Exception {
+    TestFeatureStore testFeatureStore = new TestFeatureStore();
+    LDConfig config = new LDConfig.Builder()
+            .startWaitMillis(10L)
+            .stream(false)
+            .featureStore(testFeatureStore)
+            .build();
+
+    expect(initFuture.get(10L, TimeUnit.MILLISECONDS)).andReturn(new Object());
+    expect(pollingProcessor.start()).andReturn(initFuture);
+    expect(pollingProcessor.initialized()).andReturn(true).times(2);
+    replayAll();
+
+    client = createMockClient(config);
+
+    testFeatureStore.setIntegerValue("key", 1);
+    assertTrue("Flag is known", client.isFlagKnown("key"));
+    assertFalse("Flag is unknown", client.isFlagKnown("unKnownKey"));
+    verifyAll();
+  }
+
+  @Test
+  public void testIsFlagKnownCallBeforeInitialization() throws Exception {
+    TestFeatureStore testFeatureStore = new TestFeatureStore();
+    LDConfig config = new LDConfig.Builder()
+            .startWaitMillis(10L)
+            .stream(false)
+            .featureStore(testFeatureStore)
+            .build();
+
+    expect(initFuture.get(10L, TimeUnit.MILLISECONDS)).andReturn(new Object());
+    expect(pollingProcessor.start()).andReturn(initFuture);
+    expect(pollingProcessor.initialized()).andReturn(false).times(1);
+    replayAll();
+
+    client = createMockClient(config);
+
+    testFeatureStore.setIntegerValue("key", 1);
+    assertFalse("Flag is marked as unknown", client.isFlagKnown("key"));
+    verifyAll();
+  }
+
   @Test
   public void testUseLdd() throws IOException {
     LDConfig config = new LDConfig.Builder()