Jackson throws JsonMappingException on deserialize; demands single-String constructor?

Question

Another question, but it relates to this one: Deserializing JSON with Jackson - Why JsonMappingException "No suitable constructor"?

This time I am getting

Answer 1

The exception suggests that the JSON value you have is a String, something like:

{ "protocol" : "http" }

or perhaps "double-quoted JSON":

"\"{\"property\":\"value\"}\"

when trying to bind like:

ProtocolContainer p = mapper.readValue(json, ProtocolContainer.class);

in which case Jackson has no properties to map, just a String. And in that case it does indeed require either a custom deserializer, or a creator method. Creator methods are either single-string-argument constructors, or single-string argument static methods: the difference being that only constructors can be auto-detected (this is just a practical short-cut as there can only be one such constructor, but multiple static methods).

Your solution does indeed work, just thought I'd give some background as to what is happening.

Reading through it second time it seems more likely you have double-quoted stuff (JSON in JSON): another thing to consider is to get plain JSON, if possible. But maybe that's hard to do.