How to fill an array of String from a JSON String in Java

Question

basically im getting a JSON response from the server containing a key called "references" which is a String array. It can be either empty when no previous reference is found or filled with previous references.

Here is the response i get from the server.

{"code":100,

 "name":"3PVxkvfKyUiBg3LN24ek23KceGg6350KSkLZ.html",

  "file":{
         "author":"test@test",

         "idx":"xihav-zupak-zonyf-bedid-cyvun-fahac-mykud",

         "name":"html_file",

         "references":[
                "relec-toluz",

                "rosah-vyzyh",

                "rikik-cinom"
        ]
   }
}

What I am doing at this moment is not very good, I first parse the content of references to determine the number of references then I create of new String array and put each value in it. However I am wondering if there is any proper way to do it.

Here's the code I wrote, which is not really a nice piece of code:

if(file.has("references")){
                String s = file.get("references").toString();
                int counter =0; 
                //determine the amount of elements (check if the references does not finish with ','
                if(s.length() > 2 &&  s.charAt(s.length()-2) != ','){
                    counter++;
                    System.out.println(s);
                    for(int i=0 ; i < s.length(); i++){ if( s.charAt(i) == ',' ) counter++;}
                }else {
                    counter++;
                    for(int i = 0; i < s.length() -2; i++){ if(s.charAt(i) == ',') counter++;}
                }
                JsonArray referencesList = new Gson().fromJson(s, JsonArray.class);

                if(s != null && s.length()>2 && counter !=0){
                    System.out.println("1");
                    references = new String[counter];
                    for(int i = 0 ; i < references.length ; i++){ references[i] = referencesList.get(i).getAsString();}
                }else references = new String[]{"No previous references found"};
            }

The code is working just fine for my need but is there any other way to do it more "properly" ?

Any reason you are not using a JSONParser? Check out: stackoverflow.com/questions/43724937/… — yogidilip
– yogidilip, Commented Jun 22, 2017 at 14:58
@yogidilip well i've been using Google's GSON for my whole project because i found it easier to use. That's why. — retArdos
– retArdos, Commented Jun 22, 2017 at 15:04
Then you should definitely consider using Gson's JsonParser. Leave the parsing to Gson and deal only with the resulting JsonElement. — Ishnark
– Ishnark, Commented Jun 22, 2017 at 15:07
Agree with most comments, do not use 'manual code' but ready and tested parser — Jacek Cz
– Jacek Cz, Commented Jun 23, 2017 at 9:38

Zineb Errahmouni · Accepted Answer · 2017-06-22 15:04:52Z

0

if you wan to do this properly, you need before to create a pojo class for your json

public class ClassName{

private String code;
private String name;
private MyFile file;
......
}

public class MyFile{

private String author;
private String idx;
......
}

Now after that, you're ready to map your json on your pojo object, you can do it easly using jackson.


for your documentation

https://github.com/FasterXML/jackson-docs

So you need to add jackson on your project and you can do something like this for your mapping.

ObjectMapper mapper = new ObjectMapper();
String jsonInString = "{'name' : 'qdqsdqs'}";


//JSON from URL to Object
ClassName result = mapper.readValue(jsonInString , ClassName.class);

answered Jun 22, 2017 at 15:04

Zineb Errahmouni

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Comments

Ishnark · Accepted Answer · 2017-06-22 15:51:48Z

A good start would be to parse the Json using a Json Parser. Since you're using Gson, you should look into JsonParser to do your parsing. Better not to do it manually.

Some key steps include:

Parse the Json (I'll take the json you gave me and use it as a String, but you can just as easily parse it from a file) and get a JsonElement
Look at the file member of the JsonElement, which is in turn a JsonElement and look at that JsonElement's references member, which you know is a JsonArray.

Iterate through the JsonArray and add to a list of Strings. Return that list of Strings as a String[]

public static void main(String[] args) {
    String json = "{\"code\":100,\n" +
            "\n" +
            " \"name\":\"3PVxkvfKyUiBg3LN24ek23KceGg6350KSkLZ.html\",\n" +    
            "\n" +
            "  \"file\":{\n" +
            "         \"author\":\"test@test\",\n" +
            "\n" +
            "         \"idx\":\"xihav-zupak-zonyf-bedid-cyvun-fahac-mykud\",\n" +
            "\n" +
            "         \"name\":\"html_file\",\n" +
            "\n" +
            "         \"references\":[\n" +
            "                \"relec-toluz\",\n" +
            "\n" +
            "                \"rosah-vyzyh\",\n" +
            "\n" +
            "                \"rikik-cinom\"\n" +
            "        ]\n" +
            "   }\n" +
            "}";
    JsonElement element = new JsonParser().parse(json);
    System.out.println(Arrays.toString(getReferences(element)));

}

private static String[] getReferences(JsonElement jsonElement) {
    List<String> refList = new ArrayList<>();
    JsonArray references = jsonElement.getAsJsonObject().get("file").getAsJsonObject().get("references").getAsJsonArray();
    references.forEach((reference) -> refList.add(reference.getAsString()));
    return refList.toArray(new String[0]);
}

retArdos · Accepted Answer · 2017-06-27 07:44:29Z

I was parsing on my own and not doing this right. So I rewrote some part, removed the counter part and just discovered the size() method for JSonArray which I had not checked before.

My final piece of code is shorter and easier to read.

 String[] references = null;

 String repCode = "
 {
   "code":100,

   "name":"3PVxkvfKyUiBg3LN24ek23KceGg6350KSkLZ.html",

   "file":{
     "author":"test@test",

     "idx":"xihav-zupak-zonyf-bedid",

     "name":"random",

     "references":[
            "relec-toluz",

            "rosah-vyzyh",

            "rikik-cinom"
      ]
   }
}"

The String repCode is the response I get from the server that I query.

JsonObject file = new Gson().fromJson(repCode.get("file").toString(),JsonObject.class);

if(file.has("references") &&  file.get("references").isJsonArray()){
    JsonArray referencesList = file.get("references").getAsJsonArray();

    if(referencesList.size() != 0){
        references = new String[referencesList.size()];
        for(int i = 0 ; i < references.length ; i++){
             references[i] = referencesList.get(i).getAsString();
        }
    }else references = new String[]{"No previous references found"};
}

Finally to display:

 for(String ref: references){
        System.out.println("Ref: " + ref);
    }

Which give the following output:

Ref: relec-toluz
Ref: rosah-vyzyh
Ref: rikik-cinom

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