Develop Reference

Null pointer observed while trying to fetch the object value from JSON array

I'm trying to loop the calls: JSON array and trying to fetch the machine details JSON object which is present under calls JSON array list as like below:
{
"<dynamicValue>":{
"type":"CORR-ID",
"tags":[
{
"name":"9VB6454145983212H",
"flags":[
"FLAG_DYNAMIC_VALUE",
"FLAG_ID_LOOKUP_SUPPORTED"
]
}
],
"callSummary":[
{
"colo":"lvs",
"pool":"amazon_paymentsplatformserv",
"machine":"stage2utb29958"
},
{
"colo":"lvs",
"pool":"amazon_elmoserv",
"machine":"msmamoserv_0"
},
{
"colo":"lvs",
"pool":"amazon_xopaymentgatewayserv",
"machine":"msmastmentgatewayserv_1"
},
{
"colo":"lvs",
"pool":"amazon_paymentapiplatserv",
"machine":"msmaentapiplatserv_2"
},
{
"colo":"lvs",
"pool":"amazon_userlifecycleserv_ca",
"machine":"stage2utb91581"
},
{
"colo":"lvs",
"pool":"amazon_dafproxyserv",
"machine":"msmasfproxyserv_1"
},
{
"colo":"lvs",
"pool":"paymentserv",
"machine":"te-alm-15757_paymentexecutionserv_0",
"calls":[
{
"colo":"lvs",
"pool":"fimanagementserv_ca",
"machine":"msmgementserv_ca_20"
},
{
"colo":"lvs",
"pool":"fimanagementserv_ca",
"machine":"msmasgementserv_ca_4"
}
]
}
]
}
}
The above JSON file which I stored in String variable and trying to fetch the machine details which is under calls: JSON ARRAY by using below code.
Code:
public static void getHttpUrlformachineList(String response, String CalId, String componentName)
throws Exception
{
//System.out.println(response);
Map<String, String> data = new HashMap<String, String>();
JSONParser parser = new JSONParser();
JSONObject object = (JSONObject) parser.parse(response);
JSONObject getValue = (JSONObject) object.get(CalId.trim()); //CalId is the dynamic value that mentioned in the JSON input file
JSONObject getCalSummary = (JSONObject) object.get("callSummary");
JSONArray arrays=(JSONArray) getCalSummary.get("calls");
System.out.println(arrays.size()); // return null pointer
}
Error:
java.lang.NullPointerException: null
at com.online.amazon.hadoop.cal.swagger.utils.Utils.getHttpUrlformachineList(Utils.java:112) ~[classes/:na]
If you notice that calls Array List will not be available in all the callSummary JSON Array, and It will be dynamic and can be available under any component that listed above.
So I just want to dynamically get the calls: JSON array and iterate and fetch machine details.
Can someone help me to achieve this?
Note: I'm using JSON-Simple library to parse and iterate the JSON. It would be great if I get solution on the same.
Updated:
I also tried to create callSummary as JSON array and loop that array to get each JSON object and tried to find the calls but this is also leads to Null pointer.
Also the calls json array is not index specific. It can be anywhere in the payload. It may or may not be there in the payload. I just need to handle if it's exist in any of the component then I need to fetch that machine details

change
JSONArray arrays=(JSONArray) getCalSummary.get("calls");
to
JSONArray arrays= getCalSummary.getJSONArray("calls")
and all other functions where you get objects instead of "get" you should use "getJSONObject", "getString" etc.. then you dont have to cast,
also im pretty sure its not arrays.size() its arrays.length() if you are using package org.json.JSONArray but since key "calls" doesnt exist in every "callSummary" you should check if its null or not before.

You should match the types as specified in your JSON string:
public static void getHttpUrlformachineList(String response, String CalId, String componentName)
throws Exception
{
//System.out.println(response);
Map<String, String> data = new HashMap<String, String>();
JSONParser parser = new JSONParser();
JSONObject object = (JSONObject) parser.parse(response);
JSONObject getValue = (JSONObject) object.get(CalId.trim()); //CalId is the dynamic value that mentioned in the JSON input file
JSONArray getCalSummary = (JSONArray) object.get("callSummary"); // callSummary is a JSONArray, not JSONObject
for (int i = 0; i < getCalSummary.length(); i++) {
JSONObject obj = getCalSummary.getJSONObject(i);
if (obj.has("calls")) {
// grab calls array:
JSONArray callsArray = obj.getJSONArray("calls");
}
}
}
Here, you should also check your JSON values with .has(...) method to avoid getting JSONException if a field doesn't exists in your JSONObject.

How to access JSON value?

Very new to JSON, this is probably very simple but I'm not sure how to access the "coordinates" in this JSON I know how to go from resourceSets to resources but get stuck at "point":
{
"resourceSets":[
{
"estimatedTotal":1,
"resources":[
{
"__type":"Location:http:\/\/schemas.microsoft.com\/search\/local\/ws\/rest\/v1",
"bbox":[
51.3223903,
-0.2634519,
51.3246386,
-0.2598541
],
"name":"name",
"point":{
"type":"Point",
"coordinates":[
51.3235145,
-0.261653
]
}
}
]
}
]
}
My code so far:
JSONParser parser = new JSONParser();
JSONObject jObj = (JSONObject)parser.parse(result);
JSONArray jsonArray = (JSONArray)jObj.get("resourceSets");
for (int i = 0; i < jsonArray.size(); i ++) {
JSONObject jObjResourceSets = (JSONObject)jsonArray.get(i);
JSONArray jsonArray2 = (JSONArray)jObjResourceSets.get("resources");
System.out.println("Coords" + jObjResourceSets.get("point"));
}

Lets analyse what you're doing (and need to be doing), step by step, in order to get the "coordinates".
First of all, JSON is a great language to transfer static data. It works like a dictionary, where you have a key and the respective value. The key should always be a String, but the value can be a String, an int/double or even an array of other JSON objects. That's what you have.
For instance, "estimatedTotal" is an element (JSONObject) from the "resourceSet" array (JSONArray).
JSONArray jsonArray = (JSONArray)jObj.get("resourceSets");
What you're saying here is straight forward: from your overall JSONObject - jObj - you want to extract the array with key "resourceSets".
Now you have direct access to "resourceSets" array elements: "estimatedTotal", "resources", etc. So, by applying the same logic, in order to access "coordinates" we need to access the "resources" array. And by that I mean to create a JSONArray object like we did before.
JSONArray jsonResourcesArray = (JSONArray)jObjResourceSets.get("resources");
I hope it's clear what's the content of jsonResourcesArray here. It's the JSON array of "__type", "bbox", "name", "point", (...). The Coordinates howevere are inside "point" JSON object. How do we access it?
JSONObject jsonPointObject = (JSONObject) jsonResourcesArray.get("point");
And you know by know that "jsonPointObject" has as its values the following JSON objects: "type" and "coordinates". Coordinates is an array of values, so do we have to use JSONArray or JSONObject?
JSONArray jsonCoordinatesArray = (JSONArray) jsonPointObject.get("coordinates");
From which we mean: from the jsonPointObject we want to extract the array that has key "coordinates". Now your array is a JSONArray with values of jsonCoordinatesArray.get(0) and jsonCoordinatesArray.get(0).
Now you have, not only the code to get those values, but the understanding of how JSON works and how Java interacts with it so you can solve any Json problem from now on.

Normally this code works for the given JSON object. However I'll put the tested formatted JSON value below the java code so you can test it as well.
Note that this code will get you all the coordinates of all the elements in your object.
public static void main(String[] args) throws Exception {
String result = getJsonString();
// Getting root object
JSONParser parser = new JSONParser();
JSONObject jObj = (JSONObject)parser.parse(result);
// Getting resourceSets Array
JSONArray jsonArray = (JSONArray)jObj.get("resourceSets");
for (int i = 0; i < jsonArray.size(); i++) {
// Getting the i object of resourceSet
JSONObject jObjResourceSets = (JSONObject) jsonArray.get(i);
// Getting resources list of the current element
JSONArray jsonArray2 = (JSONArray) jObjResourceSets.get("resources");
for (int j = 0; j < jsonArray2.size(); j++) {
// Getting the j resource of the resources array
JSONObject resource = (JSONObject) jsonArray2.get(j);
// Getting the point object of the current resource
JSONObject point = (JSONObject) resource.get("point");
// Getting the coordinates list of the point
JSONArray coordinates = (JSONArray) point.get("coordinates");
for (int k = 0; k < coordinates.size(); k++) {
System.out.println("Coordinates[" + k + "]: " + coordinates.get(k));
}
// Printing an empty line between each object's coordinates
System.out.println();
}
}
}
The tested JSON Object:
{
"resourceSets":[
{
"estimatedTotal":1,
"resources":[
{
"__type":"Location:http:\/\/schemas.microsoft.com\/search\/local\/ws\/rest\/v1",
"bbox":[
51.3223903,
-0.2634519,
51.3246386,
-0.2598541
],
"name":"name",
"point":{
"type":"Point",
"coordinates":[
51.3235145,
-0.261653
]
}
}
]
}
]
}
If it worked please mark it as the answer.
Good luck ^^
B.

You need the following piece of code to get the data.
JSONArray jsonArray2 = (JSONArray)jObjResourceSets.get("resources");
/**
* here we should note that the "resources" is only having one JSON object hence we can take it as below
* from 0th index using ((JSONObject)jsonArray2.get(0)) these piece of code and the next part is to take the point JSONObject
* from the object.
*/
JSONObject temp = (JSONObject)((JSONObject)jsonArray2.get(0)).get("point");
System.out.println("Coords"+temp.get("coordinates")); //this will give you the coordinates array
//now if you want to do further processing, traverse in the jsonArray like below
JSONArray arr= (JSONArray)temp.get("coordinates");
System.out.println("X coordinate:"+arr.get(0));
System.out.println("Y coordinate:"+arr.get(1));
For more information and further details on JSONObject and JSONArray you can go through this linkparsing-jsonarray-and-jsonobject-in-java-using-json-simple-jar
json-simple-example-read-and-write-json

count key value in JSON and extract values

I have following JSONObject (not array, which I don't mind to convert). I am trying to do two things:
get the count of genre entry as "poetry" (count = 2).
get the key value of author name and genre:
authorName = malcolm
genreName = newsarticle
authorName = keats
genreName = poetry
{ "AddressBook" :{
"Details" :{
"authorname" :{
"Author-malcolm":{
"genre" :"poetry"
}
"Author-keats":{
"genre" :"poetry"
}
}
}
}
}
Code which I tried:
public static void main(String[] args) throws Exception, IOException, ParseException {
JSONParser parser = new JSONParser();
Object obj = parser.parse(new FileReader("My path to JSON"));
JSONObject jsonObject = (JSONObject) obj;
JSONArray arrayhere = new JSONArray();
arrayhere.add(obj);
System.out.println(arrayhere);
int count = 0;
for(int i = 0; i < arrayhere.size(); i++) {
JSONObject element = arrayhere.getJSONObject(i);//The method getJSONObject(int) is undefined for the type JSONArray
String branchName = element.getString("genre");//The method getString(String) is undefined for the type JSONObject
if(branchName.equals("poetry")) {
count ++;
}
}
System.out.println("Count f0r poetry genre=" + count);
}
}
I have looked at solutions all over. There is no question similar to this at stackoverflow. I am not sure if the procedure is correct.

A few problems here.
First, I'm not sure where you got that example JSON but you can't work with that. That's not even valid JSON Formatting.
Looks like you want something like this:
{
AddressBook:
[
{
authorname: "author-malcom",
genre:"poetry"
},
{
authorname: "author-keats",
genre: "poetry"
}
]
}
That's the structure you're trying to create in JSON.
So, you're parsing this in from a file into a JSONObject that has a key called AddressBook inside of it. That key points to an array of JSONObjects representing authors. Each of those objects will have a key called genre. You're trying to access the genre key and count on a condition.
What you did above was create attempt to create a JSONObject from an invalid string, and then add the entire JSONObject itself into the JSONArray. JSONArray.add() doesn't convert an object to an array, it literally adds it onto the array.
jsonObj => {"Name":"name1","Id":1000}
jsonArray.add(jsonObj)
jsonArray => [{"Name":"name1","Id":1000}]
That's what you did in your code above. You didn't create an array from a JSONObject, you added an object to the array.
Proper use is going to look like:
Object obj = parser.parse(new FileReader("path_to_file"));
JSONObject jobj = (JSONObject) obj;
//access key AddressBook
JSONArray author_array = jobj.getJSONArray("AddressBook");
int poetry = 0;
for(int i = 0; i < author_array.length(); i++) {
JSONObject author = (JSONObject) author_array.get(i);
if(author.getString("genre").equals("poetry")) {
poetry++;
}
}
To summarize, you're problems come from a lack of understanding about JSON Formatting and how to access elements within a JSON Object.
Paste in the sample JSONObject I gave you above here. That site will let you visualize what you're working with.

json.org Java: JSON array parsing bug [duplicate]

This question already has answers here:
How to parse JSON in Java
(36 answers)
Closed 4 years ago.
I have JSON object as follows:
member = "{interests : [{interestKey:Dogs}, {interestKey:Cats}]}";
In Java I want to parse the above json object and store the values in an arraylist.
I am seeking some code through which I can achieve this.

I'm assuming you want to store the interestKeys in a list.
Using the org.json library:
JSONObject obj = new JSONObject("{interests : [{interestKey:Dogs}, {interestKey:Cats}]}");
List<String> list = new ArrayList<String>();
JSONArray array = obj.getJSONArray("interests");
for(int i = 0 ; i < array.length() ; i++){
list.add(array.getJSONObject(i).getString("interestKey"));
}

public class JsonParsing {
public static Properties properties = null;
public static JSONObject jsonObject = null;
static {
properties = new Properties();
}
public static void main(String[] args) {
try {
JSONParser jsonParser = new JSONParser();
File file = new File("src/main/java/read.json");
Object object = jsonParser.parse(new FileReader(file));
jsonObject = (JSONObject) object;
parseJson(jsonObject);
} catch (Exception ex) {
ex.printStackTrace();
}
}
public static void getArray(Object object2) throws ParseException {
JSONArray jsonArr = (JSONArray) object2;
for (int k = 0; k < jsonArr.size(); k++) {
if (jsonArr.get(k) instanceof JSONObject) {
parseJson((JSONObject) jsonArr.get(k));
} else {
System.out.println(jsonArr.get(k));
}
}
}
public static void parseJson(JSONObject jsonObject) throws ParseException {
Set<Object> set = jsonObject.keySet();
Iterator<Object> iterator = set.iterator();
while (iterator.hasNext()) {
Object obj = iterator.next();
if (jsonObject.get(obj) instanceof JSONArray) {
System.out.println(obj.toString());
getArray(jsonObject.get(obj));
} else {
if (jsonObject.get(obj) instanceof JSONObject) {
parseJson((JSONObject) jsonObject.get(obj));
} else {
System.out.println(obj.toString() + "\t"
+ jsonObject.get(obj));
}
}
}
}}

Thank you so much to #Code in another answer. I can read any JSON file thanks to your code. Now, I'm trying to organize all the elements by levels, for could use them!
I was working with Android reading a JSON from an URL and the only I had to change was the lines
Set<Object> set = jsonObject.keySet();
Iterator<Object> iterator = set.iterator();
for
Iterator<?> iterator = jsonObject.keys();
I share my implementation, to help someone:
public void parseJson(JSONObject jsonObject) throws ParseException, JSONException {
Iterator<?> iterator = jsonObject.keys();
while (iterator.hasNext()) {
String obj = iterator.next().toString();
if (jsonObject.get(obj) instanceof JSONArray) {
//Toast.makeText(MainActivity.this, "Objeto: JSONArray", Toast.LENGTH_SHORT).show();
//System.out.println(obj.toString());
TextView txtView = new TextView(this);
txtView.setText(obj.toString());
layoutIzq.addView(txtView);
getArray(jsonObject.get(obj));
} else {
if (jsonObject.get(obj) instanceof JSONObject) {
//Toast.makeText(MainActivity.this, "Objeto: JSONObject", Toast.LENGTH_SHORT).show();
parseJson((JSONObject) jsonObject.get(obj));
} else {
//Toast.makeText(MainActivity.this, "Objeto: Value", Toast.LENGTH_SHORT).show();
//System.out.println(obj.toString() + "\t"+ jsonObject.get(obj));
TextView txtView = new TextView(this);
txtView.setText(obj.toString() + "\t"+ jsonObject.get(obj));
layoutIzq.addView(txtView);
}
}
}
}

1.) Create an arraylist of appropriate type, in this case i.e String
2.) Create a JSONObject while passing your string to JSONObject constructor as input
As JSONObject notation is represented by braces i.e {}
Where as JSONArray notation is represented by square brackets i.e []
3.) Retrieve JSONArray from JSONObject (created at 2nd step) using "interests" as index.
4.) Traverse JASONArray using loops upto the length of array provided by length() function
5.) Retrieve your JSONObjects from JSONArray using getJSONObject(index) function
6.) Fetch the data from JSONObject using index '"interestKey"'.
Note : JSON parsing uses the escape sequence for special nested characters if the json response (usually from other JSON response APIs) contains quotes (") like this
`"{"key":"value"}"`
should be like this
`"{\"key\":\"value\"}"`
so you can use JSONParser to achieve escaped sequence format for safety as
JSONParser parser = new JSONParser();
JSONObject json = (JSONObject) parser.parse(inputString);
Code :
JSONParser parser = new JSONParser();
String response = "{interests : [{interestKey:Dogs}, {interestKey:Cats}]}";
JSONObject jsonObj = (JSONObject) parser.parse(response);
or
JSONObject jsonObj = new JSONObject("{interests : [{interestKey:Dogs}, {interestKey:Cats}]}");
List<String> interestList = new ArrayList<String>();
JSONArray jsonArray = jsonObj.getJSONArray("interests");
for(int i = 0 ; i < jsonArray.length() ; i++){
interestList.add(jsonArray.getJSONObject(i).optString("interestKey"));
}
Note : Sometime you may see some exceptions when the values are not available in appropriate type or is there is no mapping key so in those cases when you are not sure about the presence of value so use optString, optInt, optBoolean etc which will simply return the default value if it is not present and even try to convert value to int if it is of string type and vice-versa so Simply No null or NumberFormat exceptions at all in case of missing key or value
From docs
Get an optional string associated with a key. It returns the
defaultValue if there is no such key.
public String optString(String key, String defaultValue) {
String missingKeyValue = json_data.optString("status","N/A");
// note there is no such key as "status" in response
// will return "N/A" if no key found
or To get empty string i.e "" if no key found then simply use
String missingKeyValue = json_data.optString("status");
// will return "" if no key found where "" is an empty string
Further reference to study
How to convert String to JSONObject in Java
Convert one array list item into multiple Items

There are many JSON libraries available in Java.
The most notorious ones are: Jackson, GSON, Genson, FastJson and org.json.
There are typically three things one should look at for choosing any library:
Performance
Ease of use (code is simple to write and legible) - that goes with features.
For mobile apps: dependency/jar size
Specifically for JSON libraries (and any serialization/deserialization libs), databinding is also usually of interest as it removes the need of writing boiler-plate code to pack/unpack the data.
For 1, see this benchmark: https://github.com/fabienrenaud/java-json-benchmark I did using JMH which compares (jackson, gson, genson, fastjson, org.json, jsonp) performance of serializers and deserializers using stream and databind APIs.
For 2, you can find numerous examples on the Internet. The benchmark above can also be used as a source of examples...
Quick takeaway of the benchmark: Jackson performs 5 to 6 times better than org.json and more than twice better than GSON.
For your particular example, the following code decodes your json with jackson:
public class MyObj {
private List<Interest> interests;
static final class Interest {
private String interestKey;
}
private static final ObjectMapper MAPPER = new ObjectMapper();
public static void main(String[] args) throws IOException {
MyObj o = JACKSON.readValue("{\"interests\": [{\"interestKey\": \"Dogs\"}, {\"interestKey\": \"Cats\" }]}", MyObj.class);
}
}
Let me know if you have any questions.

How to get JSON object by one of its values in Java?

Trying to parse multi-level JSON in Java.
Having JSON input in format like this:
{"object1":["0","1", ..., "n"],
"objects2":{
"x1":{"name":"y1","type":"z1","values":[19,20,21,22,23,24]}
"x2":{"name":"y2","type":"z2","values":[19,20,21,22,23,24]}
"x3":{"name":"y3","type":"z1","values":[19,20,21,22,23,24]}
"x4":{"name":"y4","type":"z2","values":[19,20,21,22,23,24]}
}
and need to get all objects from 2 by one of the attributes, e.g. get all objects with type = z1.
Using org.json*.
Tried to do something like this:
JSONObject GeneralSettings = new JSONObject(sb.toString()); //receiving and converting JSON;
JSONObject GeneralObjects = GeneralSettings.getJSONObject("objects2");
JSONObject p2;
JSONArray ObjectsAll = new JSONArray();
ObjectsAll = GeneralObjects.toJSONArray(GeneralObjects.names());
for (int i=0; i < GeneralObjects.length(); i++){
p2 = ObjectsAll.getJSONObject(i);
switch (p2.getString("type")) {
case "z1": NewJSONArray1.put(p2); //JSON array that should contain values with type z1.
break;
case "z2": NewJSONArray2.put(p2); //JSON array that should contain values with type z2.
default: System.out.println("error");
break;
}
}
}
But getting null pointer exception and overall method seems not to be so well.
Please advise, is there any way to make it easier or, what am I doing wrong?

If you're getting a NullPointerException it's most likely that you haven't initialized NewJSONArray1 and NewJSONArray2.
You didn't include their declaration, but you probably just need to do
NewJSONArray1=new JSONArray();
NewJSONArray2=new JSONArray();
before your loop.
Aside: by convention java variables should start with a lower case letter, e.g. newJSONArray1

public static void main(String[] args) {
String s =
"{\"object1\":[\"0\",\"1\",\"n\"]," +
"\"objects2\":{" +
"\"x1\":{\"name\":\"y1\",\"type\":\"z1\",\"values\":[19,20,21,22,23,24]}," +
"\"x2\":{\"name\":\"y2\",\"type\":\"z2\",\"values\":[19,20,21,22,23,24]}," +
"\"x3\":{\"name\":\"y3\",\"type\":\"z1\",\"values\":[19,20,21,22,23,24]}," +
"\"x4\":{\"name\":\"y4\",\"type\":\"z2\",\"values\":[19,20,21,22,23,24]}" +
"}}";
System.out.println(s);
JSONObject json = new JSONObject(s);
JSONObject object2 = json.optJSONObject("objects2");
if (object2 == null) {
return;
}
JSONArray result = new JSONArray();
for (Object key : object2.keySet()) {
JSONObject object = object2.getJSONObject(key.toString());
String type = object.optString("type");
if ("z1".equals(type)) {
System.out.println(object.toString());
result.put(object);
}
}
System.out.println(result);
}

You can always convert it to string and use json-path:
https://code.google.com/p/json-path/