Parse JSON String into raw Java types using Jackson?

Question

I would like to parse some JSON string the represents either an array or a map in the simplest possible way. I have the whole JSON string, no streaming is needed.

What I would like to do is something as similar as possible to this:

Object obj = parseJSON(theString);

Where obj would then hold an instance of either a Map or a List (I cannot know in advance which). The JSON object can be arbitrarily nested with maps and arrays but all types will be representable as basic Java types: String, Integer, Double, Boolean plus Map and ArrayList, nothing else.

All the simple examples I have found so far require me to know what the type is and which types I want, but I want to let all this do the JSON parser since I simply will not know in advance what I get.

If Jackson is not the best library to do this, what else could I use?

(I see lots of Java folks struggling with simple JSON problems because they're all so enamored of Jackson and it's clones.) — Hot Licks
– Hot Licks, Commented Dec 7, 2013 at 20:18

Vidya · Accepted Answer · 2013-12-07 20:19:20Z

5

All you need to do is this:

ObjectMapper mapper = new ObjectMapper();
Map<String,Object> map = mapper.readValue(theString, Map.class);

I'm pretty sure this returns a LinkedHashMap, if you care.

And in my opinion, you won't find a better serializer/deserializer for Java <-> JSON than Jackson. But there are many others like GSON.

answered Dec 7, 2013 at 20:19

Vidya

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2 Comments

jpp1 Over a year ago

The problem I had been struggling with was that I only saw examples where one had to specify, like in your example, Map or Array or my own types. I was too silly to see that I can actually just specify Object.class instead and it will do exactly what I want.

Vidya Over a year ago

Oh yes, you can do that too. I thought you wanted to be explicit about using a Map. But Object works.

jpp1 · Accepted Answer · 2013-12-07 20:29:59Z

2

Silly question, simple answer:

import com.fasterxml.jackson.databind.ObjectMapper;
ObjectMapper mapper = new ObjectMapper();
Object obj = mapper.readValue(theString, Object.class);

That seems to do exactly what I want. And it's so obvious too!

answered Dec 7, 2013 at 20:29

jpp1

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Comments

user949300 · Accepted Answer · 2013-12-07 20:27:10Z

1

Another option should you decide to ditch Jackson (Jackson is fine, I'm quite agnostic in the JSON wars) is json-simple.

JSONObject jObject = JSONValue.parse(String jsonString);

Since JSONObject extends java.util.HashMap everything should work.

answered Dec 7, 2013 at 20:27

user949300

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2 Comments

jpp1 Over a year ago

No, because if the JSON string represents an array I want a list in that case. As I found out a few seconds after posting, readValue(theString, Object.class) will do this: it will give me an ArrayList if JSON is an Array and a LinkedHashMap if the JSON is a map.

user949300 Over a year ago

I guess my question is "then what"? You have an Object that is either a Map or a List, but what can you do with it? You gonna do an instanceof? Guess I don't completely understand your question...

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