Java JSON/object to array

Question

I have a question about type casting. I have the following JSON String:

{"server":"clients","method":"whoIs","arguments":["hello"]}

I am parsing it to the following Map<String, Object>.

{arguments=[hello], method=whoIs, server=clients}

It is now possible to do the following:

request.get("arguments");

This works fine. But I need to get the array that is stored in the arguments. How can I accomplish this? I tried (for example) the following:

System.out.println(request.get("arguments")[0]);

But of course this didn't work..

How would this be possible?

Answer 1

Maybe

 System.out.println( ((Object[]) request.get("arguments")) [0]);

? You could also try casting this to a String[].

Anyway, there are more civilized ways of parsing JSON, such as http://code.google.com/p/google-gson/.

Answer 2

Most likely, value is a java.util.List. So you would access it like:

System.out.println(((List<?>) request.get("arguments")).get(0));

But for more convenient access, perhaps have a look at Jackson, and specifically its Tree Model:

JsonNode root = new ObjectMapper().readTree(source);
System.out.println(root.get("arguments").get(0));

Jackson can of course bind to a regular Map too, which would be done like:

Map<?,?> map = new ObjectMapper().readValue(source, Map.class);

But accessing Maps is a bit less convenient due to casts, and inability to gracefully handle nulls.