ObjectMapper和Class.forName（）

Question

I'm trying to use Jackson's ObjectMapper combined with Class.forName method.

private Object createObject(String json, String rootName) {
    try {
        ObjectMapper mapper = new ObjectMapper();
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,
                false);
        JsonNode root = mapper.readTree(json);
        Class clazz = Class.forName("com.model." + Finder.findClassName(rootName));
        return mapper.treeToValue(root.get("rootName"), clazz);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }

}

It's not working and I'm getting the following error message:

 Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference 

However, there are no null references because clazz variable isn't so. What could be the error cause?

Answer 1

The problem was I wrote rootName as literal String, not as variable name.

return mapper.treeToValue(root.get("rootName"), clazz); // wrong
return mapper.treeToValue(root.get(rootName), clazz);  //  correct