feature variable accessor apis (#133)

* link feature variable accessors to feature variable by value and type
* add unit tests for getFeatureVariable calling through to internals
* add unit tests to catch parsing error

Author: wangjoshuah

core-api/src/main/java/com/optimizely/ab/Optimizely.java

@@ -383,6 +383,16 @@ public void track(@Nonnull String eventName,
                                                        @Nonnull String variableKey,
                                                        @Nonnull String userId,
                                                        @Nonnull Map<String, String> attributes) {
+        String variableValue = getFeatureVariableValueForType(
+                featureKey,
+                variableKey,
+                userId,
+                attributes,
+                LiveVariable.VariableType.BOOLEAN
+        );
+        if (variableValue != null) {
+            return Boolean.parseBoolean(variableValue);
+        }
         return null;
     }
 
@@ -413,6 +423,22 @@ public void track(@Nonnull String eventName,
                                                      @Nonnull String variableKey,
                                                      @Nonnull String userId,
                                                      @Nonnull Map<String, String> attributes) {
+        String variableValue = getFeatureVariableValueForType(
+                featureKey,
+                variableKey,
+                userId,
+                attributes,
+                LiveVariable.VariableType.DOUBLE
+        );
+        if (variableValue != null) {
+            try {
+                return Double.parseDouble(variableValue);
+            }
+            catch (NumberFormatException exception) {
+                logger.error("NumberFormatException while trying to parse \"" + variableValue +
+                "\" as Double. " + exception);
+            }
+        }
         return null;
     }
 
@@ -443,6 +469,22 @@ public void track(@Nonnull String eventName,
                                                        @Nonnull String variableKey,
                                                        @Nonnull String userId,
                                                        @Nonnull Map<String, String> attributes) {
+        String variableValue = getFeatureVariableValueForType(
+                featureKey,
+                variableKey,
+                userId,
+                attributes,
+                LiveVariable.VariableType.INTEGER
+        );
+        if (variableValue != null) {
+            try {
+                return Integer.parseInt(variableValue);
+            }
+            catch (NumberFormatException exception) {
+                logger.error("NumberFormatException while trying to parse \"" + variableValue +
+                "\" as Integer. " + exception.toString());
+            }
+        }
         return null;
     }