ObjectMapper readTree() bug?

[danuvian]

It's my understanding that I can use the readTree(string) in ObjectMapper to check if a String is valid JSON.

I tried this string: "{"msg":"hello there"}messedup" and it did not throw an exception, as I expected it to, even though it's not valid JSON.

Code:
var x = "{"msg":"hello there"}messedup";
objectMapper.readTree(x);

[cowtowncoder]

Your understanding is close but not exactly accurate: by default this method only reads enough content from input to decode a single valid JSON value, and does not do anything more with any input there might still exist.

But to get what you want here, you will need to enable DeserializationFeature.FAIL_ON_TRAILING_TOKENS which will then try to consume the whole input (stream, String, whatever), and fail if there is any other content except for white space.
In this particular case it should throw a JsonParseException for unrecognized content.

You can enable that feature either on ObjectMapper or ObjectReader dynamically.