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How to retrieve json array elements from JSON object in Java?

JSONObject firstObject = (JSONObject) jsonParser.parse(new FileReader(firstNamesPath));
I have this JSONObject, and I want to be able to access elements in the array inside of it. The object opens successfully, I just don't know how to access the array called "firstNames". It is in a file, and the object looks like this.
{
"firstNames": [
"Aaron",
"Abigail",
"Albert",
"Bob"
]
}
Edit: I am using org.json.simple.JSONObject . If this is not recommended, I am more than willing to change it.

There are several ways to retrieve the json array value:
Assume we have a jsonString
jsonString = "{\n" + " \"firstNames\": [ \n" + " \"Aaron\",\n" + " \"Abigail\",\n" + " \"Albert\",\n" + " \"Bob\"\n" + " ]\n" + "}";
(since many classes share similar names, I am using the groupId and artifactId for distinction.)
Simple cases: use generic JSONObjects and JSONArrays.
json-simple (which OP is using) json-simple website, maven :
org.json.simple.parser.JSONParser jsonParser = new org.json.simple.parser.JSONParser();
org.json.simple.JSONObject firstObject = (org.json.simple.JSONObject) jsonParser.parse(jsonString);
org.json.simple.JSONArray jsonArray = (org.json.simple.JSONArray) firstObject.get("firstNames");
System.out.println(jsonArray);
JSON in Java (mentioned in adendrata's answer): JSON-Java doc, maven
org.json.JSONObject secondObject = new org.json.JSONObject(jsonString);
org.json.JSONArray jsonArray2 = secondObject.getJSONArray("firstNames");
System.out.println(jsonArray2);
gson: Gson, maven
com.google.gson.JsonObject thirdObject = com.google.gson.JsonParser.parseString(jsonString).getAsJsonObject();
System.out.println(thirdObject.get("firstNames").getAsJsonArray());
For more complicated use cases, if you'd like to define your own class, and want to deserialize JSON string to your class, then you can use Gson or Jackson:
// Create your own class:
/*
public class YourOwnClass {
private List<String> firstNames;
public List<String> getFirstNames() {
return firstNames;
}
}
*/
Gson gson = new Gson();
YourOwnClass customObject1 = gson.fromJson(jsonString, YourOwnClass.class);
System.out.println(customObject1.getFirstNames());
ObjectMapper mapper = new ObjectMapper();
YourOwnClass customObject2 = mapper.readValue(jsonString, YourOwnClass.class);
System.out.println(customObject2.getFirstNames());

you can use JSONArray to get array type of Json and looping to access each index
example:
JSONArray array = firstObject.getJSONArray("firstNames");
for (int i = 0; i < array.length(); i++) {
System.out.println("Hello i'm " + array.get(i));
}

Try to use this : com.alibaba.fastjson.JSONObject, and here's the dependency:
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>fastjson</artifactId>
<version>1.2.41</version>
</dependency>
Then you can directly use the getJSONArray method the answer shown above.

reading data from nested JSON Object using java

i am struggling with reading some values from JSON object which i get it when i hit REST API..
MY GOAL: i need to iterate over each set of data inside data object array check the value of TRAN_ID and take action accordingly.
below is the format of data
{
"data": [
{
"CUST_ID": "CUST7",
"EXPRY_DATE": null,
"PARAMS": "[{TRAN_IND:savings},{TRAN_TYP:Debit},{country:US}]"
},
{
"CUST_ID": "CUST8",
"EXPRY_DATE": null,
"PARAMS": "[{TRAN_IND:current},{TRAN_TYP:Debit},{country:US}]"
}
]
}
it looks easy and i have tried multiple solutions out there on internet but i dont know it doesnt work for me and i get below error while reading "PARAMS" and converting it to JSONArray for further processing
Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to org.json.simple.JSONArray
What i have tried:
private static void jsonParser(String jsonStr) throws ParseException {
JSONObject data= (JSONObject)JSONValue.parse(jsonStr );
JSONArray jsonObj = (JSONArray)data.get("data");
JSONObject JsonRow = (JSONObject)jsonObj.get(0);
JSONArray servParam= (JSONArray) JsonRow.get("PARAMS");
String tran_ind=(String) servParam.get(0);
System.out.println( tran_ind);
}

I'm guessing this is what you what?
try{
JSONObject obj = new JSONObject(sample);
JSONArray data = obj.getJSONArray("data");
for(int i=0; i<data.length(); i++){
JSONObject detail = data.getJSONObject(i);
detail.getString("CUST_ID"); //here is the customer id
detail.getString("EXPRY_DATE"); //here is the exp date
JSONArray params = detail.getJSONArray("PARAMS");
for(int j=0; j<params.length(); j++){
// {TRAN_IND:current},{TRAN_TYP:Debit},{country:US}
JSONObject res = params.getJSONObject(j);
String tran_ind = res.toString();
String tran_type = res.toString();
String country = res.toString();
out.println(tran_ind + " " +tran_type + " " + country);
}
}
}catch (JSONException ex){
ex.printStackTrace();
}

Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to org.json.simple.JSONArray
=> Because you are trying to parse String value "[{TRAN_IND:savings},{TRAN_TYP:Debit},{country:US}]" into the JsonArray by code:
JSONArray servParam= (JSONArray) JsonRow.get("PARAMS");

Params seems to be a String, actually.
Don't write your own parser. If you only need to read that string in each element of the array, I would simply cast the whole JSON to a Map with Jackson:
HashMap<String,Object> parsed =
new ObjectMapper().readValue(JSON_SOURCE, HashMap.class);
and then iterate over the "data" element (which would be a list of maps).
List<Map> data = (List) parsed.get("data");

The real problem is that those are not nested JSON strings. That would be
"PARAMS": "[{\"TRAN_IND\":\"current\"},{\"TRAN_TYP\":\"Debit\"},{\"country\":\"US\"}]"
so "text" parts are surrounded by "-s inside (which have to be escaped as \"-s).
In that case you could write
String json=
"{\n"+
" \"data\": [\n"+
" {\n"+
" \"CUST_ID\": \"CUST7\",\n"+
" \"EXPRY_DATE\": null,\n"+
" \"PARAMS\": \"[{\\\"TRAN_IND\\\":\\\"savings\\\"},{\\\"TRAN_TYP\\\":\\\"Debit\\\"},{\\\"country\\\":\\\"US\\\"}]\"\n"+
" },\n"+
" {\n"+
" \"CUST_ID\": \"CUST8\",\n"+
" \"EXPRY_DATE\": null,\n"+
" \"PARAMS\": \"[{\\\"TRAN_IND\\\":\\\"current\\\"},{\\\"TRAN_TYP\\\":\\\"Debit\\\"},{\\\"country\\\":\\\"US\\\"}]\"\n"+
" }\n"+
" ]\n"+
"}";
// Print input for clarity:
System.out.println(json);
JSONObject data= (JSONObject)JSONValue.parse(json);
JSONArray jsonObj = (JSONArray)data.get("data");
JSONObject JsonRow = (JSONObject)jsonObj.get(0);
// parse nested JSON
JSONArray servParam= (JSONArray)JSONValue.parse((String)JsonRow.get("PARAMS"));
// array element is an object ({"TRAN_IND":"savings"}), so toString has to be used:
String tran_ind=servParam.get(0).toString();
System.out.println(tran_ind);
(The backslash-heaps are there because double-quotes had to be escaped in source code, and also the suggested escaped double quotes. So they would not appear in a JSON file. Try the code in action, it prints the JSON it works on)
So (JSONArray)JSONValue.parse((String)JsonRow.get("PARAMS")) would get and parse the nested JSON.
But now you either have to rework the code what generates your input, or parse the nested non-JSON manually.

You can use below code for parsing.
String servParam = (String) JsonRow.get("PARAMS");
String servParamSplitted[] = servParam.substring(1, servParam.length() - 1).split(",");
String traind_id[] = servParamSplitted[0].substring(1, servParamSplitted[0].length() - 1).split(":");
String train_id=traind_id[1];
I like to add that your JSON should be like below format.
{
"data": [
{
"CUST_ID": "CUST7",
"EXPRY_DATE": null,
"PARAMS": [{"TRAN_IND":"savings"},{"TRAN_TYP":"Debit"},{"country":"US"}]
},
{
"CUST_ID": "CUST8",
"EXPRY_DATE": null,
"PARAMS": [{"TRAN_IND":"current"},{"TRAN_TYP":"Debit"},{"country":"US"}]
}
]
}
So, we can parse it using below code.
JSONArray servParam = (JSONArray) JsonRow.get("PARAMS");
JSONObject jsonObjectTrainID = (JSONObject) servParam.get(0);
String TrainIDValue = (String) jsonObjectTrainID.get("TRAN_IND");

Java: Loop through JSON string (cant convert to JsonArray (gson)

i get a json object via an api:
Gson gson = new Gson();
JsonObject users = gson.fromJson(reader, JsonObject.class)
this is my json object:
{"users":"[{\"user_id\": \"100011\", \"name\": \"Tim Clark\"}, {\"user_id\": \"100083\", \"name\": \"Timmy Kent\"}]"}
and i try to loop through all users
JsonArray usersArray = users.getAsJsonArray();
for (JsonElement ua : usersArray) {
JsonObject ua = ua.getAsJsonObject();
String name = ua.get("name").getAsString();
System.out.println(name);
}
also tried this
JsonArray usersArray = users.get("users").getAsJsonArray();
for (JsonElement ua : usersArray) {
JsonObject ua = ua.getAsJsonObject();
String name = ua.get("name").getAsString();
System.out.println(name);
}
But I get always exceptions like this
java.lang.IllegalStateException: Not a JSON Array: "[{\"user_id\": \"100011\", \" ....
In my opinion it is a valid json array, what to I miss?

Your JsonArray is between quotes: it's evaluated as a String
{"users":[{\"user_id\": \"100011\", \"name\": \"Tim Clark\"}, {\"user_id\":
\"100083\", \"name\": \"Timmy Kent\"}]}
should work (quotes inside the array don't need to be escapted as well, like "users")

How can I control a empty JsonArray, if string is " [ ] " [duplicate]

This question already has answers here:
how to check if a JSONArray is empty in java?
(4 answers)
Closed 5 years ago.
my json string is
String RESPONSE = " { "Table": [] } ";
and I use
JSONObject jsonObj = new JSONObject(RESPONSE);
JSONArray contacts = jsonObj.getJSONArray("Table");
Therefore, contacts = [] I mean empty.
How can I control that array is empty.
After this controller I use this command
JSONObject c = contacts.getJSONObject(0);
Of course is not empty :)

You can use length function:
JSONObject jsonObj = new JSONObject(RESPONSE);
JSONArray contacts = jsonObj.getJSONArray("Table");
if(contacts.length() > 0 ) {
JSONObject c = contacts.getJSONObject(0);
}

You could use the isNull() function.
JSONObject jsonObj = new JSONObject(RESPONSE);
JSONArray contacts = jsonObj.getJSONArray("Table");
if(!contacts.isNull(0)) {
JSONObject c = contacts.getJSONObject(0);
}

How to generate JSON string in Java using net.sf.json?

I am struggling to generate JSON String in Java.
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
JSONArray ja = new JSONArray();
JSONObject js = new JSONObject();
JSONObject j = new JSONObject();
String s = "[{\"shakil\",\"29\",\"7676\"}]";
js.put("id", "1");
js.put("data", s);
ja.add(js);
j.put("rows", ja);
System.out.println(j.toString());
actual output:
{"rows":[{"id":"2","data":"[{\"shakil\",\"29\",\"7676\"}]"}]}
expected output:
{"rows":[{"id":"2","data":["shakil", "29","7676"]}]};

Your s is a String which is not unquoted when put into a JSONObject. You must build another JSONArray for the value of data:
// using http://jettison.codehaus.org/
JSONObject outerObject = new JSONObject();
JSONArray outerArray = new JSONArray();
JSONObject innerObject = new JSONObject();
JSONArray innerArray = new JSONArray();
innerArray.put("shakil");
innerArray.put("29");
innerArray.put("7676");
innerObject.put("id", "2");
innerObject.put("data", innerArray);
outerArray.put(innerObject);
outerObject.put("rows", outerArray);
System.out.println(outerObject.toString());
Result:
{
"rows": [
{
"id": "2",
"data": [
"shakil",
"29",
"7676"
]
}
]
}

Write
String[] s = new String[] {"shakil", "29" , "7676"};
instead of
String s = "[{\"shakil\",\"29\",\"7676\"}]";

Check out gson, it'll provide you with a whole lot of options for serializing/deserializing your Java objects to/from JSON.
Example taken from the page
Gson gson = new Gson();
int[] ints = {1, 2, 3, 4, 5};
String[] strings = {"abc", "def", "ghi"};
//(Serialization)
gson.toJson(ints); ==> prints [1,2,3,4,5]
gson.toJson(strings); ==> prints ["abc", "def", "ghi"]
//(Deserialization)
int[] ints2 = gson.fromJson("[1,2,3,4,5]", int[].class);

Finally found answer for net.sf.json
JSONArray data1 = new JSONArray();
data1.add("shakil");
data1.add("29");
data1.add("100");
JSONObject inner1 = new JSONObject();
inner1.put("id", "1");
inner1.put("data", data1);
JSONArray list2 = new JSONArray();
list2.add(inner1);
JSONObject finalObj = new JSONObject();
finalObj.put("rows", list2);
System.out.println(finalObj);

Not being able to declare a JSON string in Java is huge pain. Mainly due to (a) no multiline strings (b) escaping double quotes makes it a mess wrt readability.
I work around this by using single quotes to declare the JSON string (using the standard multiline concatenation). Nothing fancy:
String jsonStr =
"{" +
"'address': " +
"{" +
"'name': '" + name + "'," +
"'city': '" + city + "'," +
"'street1': '"+ street1 +"'," +
"'street2': '"+ street2 +"'," +
"'zip': '" + zip + "', " +
"'state':'" + state + "'," +
"'country': '" + country + "'," +
"'phone': '" + phone + "'" +
"}" +
"}";
jsonStr = MyUtil.requote(jsonStr);
System.out.println(jsonStr);
MyUtil
public static String requote(String jsonString) {
return jsonString.replace('\'', '"');
}
Some might find this more cumbersome than declaring a Map but this works for me when I have to build a JSON with just string syntax.

I see a lot of problems when writing a json as String directly without using a Objectmapper or similar.
I would suggest you to write your Json (as you defined it):
{"rows":[{"id":"2","data":["shakil", "29","7676"]}]}
and then simply use this little online tool: http://www.jsonschema2pojo.org/
Which can convert a simply Json a Java-Class also with multiple classes. You can there choose during generation if you want to use Gson or Jackson later.
Gson is a little bit lightweighter and may is better for beginning. I prefer Jackson because you can create something like a computed property - but that's already to much detail.
https://code.google.com/p/google-gson/
After adding Gson all you need to do is:
Gson gson = new Gson();
MyGeneratedClass target = new MyGeneratedClass();
String json = gson.toJson(target);
As voila: you have generated a simple json without thinking about how to change it later!