Minor improvement wrt #546: prevent attempts to use JsonTypeInfo.As.EXTERNAL_PROPERTY for default typing (throw IllegalArgumentException if attempted)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/ObjectMapper.java

@@ -1073,12 +1073,23 @@ public ObjectMapper enableDefaultTyping(DefaultTyping dti) {
      * Method for enabling automatic inclusion of type information, needed
      * for proper deserialization of polymorphic types (unless types
      * have been annotated with {@link com.fasterxml.jackson.annotation.JsonTypeInfo}).
+     *<P>
+     * NOTE: use of {@link JsonTypeInfo.As#EXTERNAL_PROPERTY} is <b>NOT SUPPORTED</b>;
+     * and attempts of do so will throw an {@link IllegalArgumentException} to make
+     * this limitation explicit.
      * 
      * @param applicability Defines kinds of types for which additional type information
      *    is added; see {@link DefaultTyping} for more information.
      */
     public ObjectMapper enableDefaultTyping(DefaultTyping applicability, JsonTypeInfo.As includeAs)
     {
+        /* 18-Sep-2014, tatu: Let's add explicit check to ensure no one tries to
+         *   use "As.EXTERNAL_PROPERTY", since that will not work.
+         */
+        if (includeAs == JsonTypeInfo.As.EXTERNAL_PROPERTY) {
+            throw new IllegalArgumentException("Can not use includeAs of "+includeAs);
+        }
+        
         TypeResolverBuilder<?> typer = new DefaultTypeResolverBuilder(applicability);
         // we'll always use full class name, when using defaulting
         typer = typer.init(JsonTypeInfo.Id.CLASS, null);

src/test/java/com/fasterxml/jackson/databind/jsontype/TestDefaultForObject.java

@@ -349,6 +349,18 @@ public void testFeature432() throws Exception
         String json = mapper.writeValueAsString(new BeanHolder(new StringBean("punny")));
         assertEquals("{\"bean\":{\"*CLASS*\":\"com.fasterxml.jackson.databind.jsontype.TestDefaultForObject$StringBean\",\"name\":\"punny\"}}", json);
     }
+
+    public void testNoGoWithExternalProperty() throws Exception
+    {
+        ObjectMapper mapper = new ObjectMapper();
+        try {
+            mapper.enableDefaultTyping(ObjectMapper.DefaultTyping.JAVA_LANG_OBJECT,
+                    JsonTypeInfo.As.EXTERNAL_PROPERTY);
+            fail("Should not have passed");
+        } catch (IllegalArgumentException e) {
+            verifyException(e, "Can not use includeAs of EXTERNAL_PROPERTY");
+        }
+    }
 
     /*
     /**********************************************************