Java decode JSON

Question

Im trying to decode json string to Map.

I know there were many questions like this, but I need quite specific format. For example, I have json string:

{
 "map": {
 "a": "b",
 "c": "d",
 },
 "map2": {
 "aa": "bb",
 "cc": "dd",
 },
 "something": "a",
 "something2": "b"
}

And I need to have results like:

"map.a" => "b"
"map.c" => "d"
"map2.aa" => "bb"
"map2.cc" => "dd"
"something" => "a"
"something2" => "b"

Im sure that the keys won't contain any dots. I looked at few JSON libraries, but I don't need so many functions, just to decode and store in Java map. If there is no simple way, I gonna write own algorithm for this, I hope it won't be so hard...

Thanks for any help.

• Philipp: Even when you use your own algorithm to generate the keys in dot-notation, I would still recommend you to use a decoder library. There are too many edge-cases which could cause nasty bugs, like string escaping rules.

Answer 1

I used org.codehaus.jackson. Do the following:

 HashMap<String, Object> content = null;
 HashMap<String, String> result = new HashMap<String, String>();
 try {
 JsonFactory factory = new JsonFactory();
 ObjectMapper mapper = new ObjectMapper(factory);
 TypeReference<HashMap<String, Object>> typeRef = new TypeReference<HashMap<String, Object>>() {
 };
 content = mapper.readValue(jsonString, typeRef);
 } catch (Exception ex) {
 System.out.println("Exception : " + ex);
 } 
 // now content has everything inside
 for(String s : content.keySet()){
 Object obj = content.get(s);
 if(obj instanceof String){
 result.put(s, (String)obj);
 } else {
 HashMap<String,String> hm = (HashMap<String,String>)obj;
 for(String s2: hm.keySet()){
 result.put(s+"."+s2, hm.get(s2));
 }
 }
 }

Edit: Tested, and working

Answer 2

To accurately parse JSON you'll want to define a proper parser for it, they're not terribly difficult to write just time consuming. My recommendation would be to find a fairly lightweight JSON parser and then write a decorator for it to get the map format you're looking for. Although, if you're processing large amounts of JSON you'll, unfortunately, be adding overhead.

Answer 3

I don't think you'll find an out-of-the-box solution to this, since that's a non-standard representation. My suggestion would be to use a JSON library to convert the JSON string to a Java Map, then do a depth-first traversal of that Map to transform it to your desired representation.