read dynamic json files in java and merge them

Question

I am struggling with json-parsing in java.
Is there a possibility to generate a representation of a random, not standardised json file in java? I tried to use gson but I didn't really understood if and how that might be possible.

So the jsonFile could look like this:

{ 
 "id":16875,
 "position":[1,2,5,7],
 "metadata":{
     "color":"blue",
     "id": "84779jh",
     "more":{ "some":"randomdata","absolutly":"noStructure"}
}

any key-value pairs are possible and the json file can be nested as much and as deep as it wants to. I need to get something like a java object out of it to be able to merge it with another json file. I just need the metadata part, the rest can be ignored.

So anybody any ideas how I could make that work? I would appreciate any helps :)

the json above merged with (this is the parent node, so we keep his id and position and just merge the metadata)

  { 
   "id":16zut,
   "position":[1,2,5,7],
   "metadata":{
     "color":"green",
     "id": "84ergfujh",
     "more":{ 
        "some":"randomdata",
        "even":"more",
        "absolutly":"noStructure"
     },
     "tags":[1,2,3,4,6,8,f7,h,j,f]
   }

would be:

  { 
   "id":16zut,
   "position":[1,2,5,7],
    "metadata":{
    "color":["blue", "green"],
    "id": ["84779jh","84ergfujh]",
    "more":{ "some":"randomdata","absolutly":"noStructure","even":"more"}
    "tags":[1,2,3,4,6,8,f7,h,j,f]
  }

Thanks in advance and have a nice day.

Answer 1

After seeing the json you posted i think you are trying to merger two json of with same id but different metadata id. Since the json work on the key value. you can't have two value for the same key such as in this value

"color":"blue", "green",
"id": "84779jh","84ergfujh"

unless you take color as a array. After seeing ur json you create map on the basis of the metadata id and you can add those metadata map to single metadata map

        import java.io.File;
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.HashSet;
    import java.util.Map;
    import org.codehaus.jackson.map.ObjectMapper;
    import org.codehaus.jackson.type.TypeReference;
    import com.google.common.collect.ImmutableMap;
    public class JsonFileMapExample {
        public static void main(String[] args) {
            try {
                ObjectMapper mapper = new ObjectMapper();
                // read JSON from a file
                Map<String, Object> map_json1 = mapper.readValue(new File(
                        "F:/Work/DB/work/workspace/restclient/src/json1.json"),
                        new TypeReference<Map<String, Object>>() {
                        });
                Map<String, Object> map_json2 = mapper.readValue(new File("F:/Work/DB/work/workspace/restclient/src/json2.json"),new TypeReference<Map<String, Object>>() { });
                System.out.println(map_json1);
                System.out.println(map_json2);
                Map<String, Object> map2 = (Map<String, Object>) map_json1.get("metadata");         
                Map<String, Object> map_json3 = new HashMap<String, Object>();          
                map_json3 = mergeMyTwoMaps((Map<String, Object>) map_json1.get("metadata"),(Map<String, Object>) map_json2.get("metadata"));            
                System.out.println(map_json3);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        static Map<String, Object> mergeMyTwoMaps(Map<String, Object> map1, Map<String, Object> map2) {
              return ImmutableMap.<String, Object>builder()
                  .putAll(map1)
                  .putAll(map2)
                  .build();
            }

        }

Output:

json1=  {id=16875, position=[1, 2, 5, 7], metadata={id=84779jh, color=blue, more={some=randomdata, absolutly=noStructure}}} 
json2={id=16875, position=[1, 2, 5, 7], metadata={id=84779jhdf, color=green, more={some=dsfasdf, absolutly=afdsadsf}}}
json3_aftermerged={id=16875, position=[1, 2, 5, 7], metadata={id=84779jh, color=blue, more={some=randomdata, absolutly=noStructure}},{id=16875, position=[1, 2, 5, 7], metadata={id=84779jhdf, color=green, more={some=dsfasdf, absolutly=afdsadsf}}}

Note for using this u need to have jar file from http://code.google.com/p/guava-libraries/

Answer 2

I got my problem solved and i am grateful thank you guys helped me with it. So let me share:

I read the 2 jsons both as a tree (i am using Jackson):

   ObjectMapper mapper = new ObjectMapper();
   JsonNode parent = mapper.readTree(new File(path)); 
   JsonNode child= mapper.readTree(new File(path)); 

And the merge logic isn't done yet but the basic concept is:

 Iterator<String> pIt = parent.fieldNames();
    while(pIt.hasNext())
    {
        String tempkey = pIt.next();

        if(child.path(tempkey) != null)
        {
            merged.put(tempkey,child.path(tempkey));

        }
        else{
                merged.put(tempkey,parent.path(tempkey) );
        }

    }

    try {
        String jsonString = mapper.writeValueAsString(merged);
        System.out.println(jsonString);
    } catch (JsonProcessingException e) {...}

If you think it is a dumb solution, i am open for other ideas...
But i think it might work for my needs.

greetings and thanks :)