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How to loop trough nested JSON and get value using Java, SpringBoot

I have a nested JSON that I want to loop through and get value based on key.
Data.json
{
"car": [
{
"date": 1324599600000,
"values": [
{
"name": "Audi",
"price": "11212.12"
},
{
"name": "Bmw",
"price": "22321.3"
},
{
"name": "Cittroen",
"price": "23432.2"
},
{
"name": "Tuareg",
"price": "556456.3"
}
]
}
I created 3 object models based on JSON data.
CarResponse.java
public class CarResponse {
#JsonProperty(value = "car")
List<Car> cars;
//getters,setters
Car.java
public class Car{
#JsonProperty("values")
private List<CarValue> carValue;
//getters, setters
CarValue.java
public class CarValue {
private String name;
private BigDecimal price;
//getters, setters
DataParse.java
public class DataParse{
CarResponse response;
public CarValue parse(){
CarValue carValue = new CarValue();
//NEED HELP WITH THIS PART
for(Car cars : response.getQuote()){
for(CarValue qv : cars.getCarValue()){
String type = qv.get("name").asText();
Decimal value = qv.get("price").decimalValue();
carValue.setName(qv.getName());
carValue.setPrice(qv.getPrice());
}
}
return quoteValue;
}
}
In JSON I need to check if car name is Audi and if car name is Tuareg then save it and display it.
Nested for loop part of code is not working
for(Car cars : response.getQuote()){
for(CarValue qv : cars.getCarValue()){
String type = qv.get("name").asText();
Decimal value = qv.get("price").decimalValue();
carValue.setName(qv.getName());
carValue.setPrice(qv.getPrice());
}
}
Just put it as an example of what I need to do in this step which is check for key in JSON and if it is that key with for example name = Audi then
carValue.setName(qv.getName());
With my code above I am getting this in the console.
carValue=[carValue{name=null, price=null}

Assuming that your deserialization is working correctly, you should change the part that "is not working" to:
String type = qv.getName();
BigDecimal value = qv.getPrice();
If for some reason you want to use this qv.get(key) method, you should post its implementation.
When getName and getPrice are still returning null, it means you have a problem with the deserialization, for example a wrong setter method name. Still, without the implementation is impossible to understand.
Here is the official documentation of Jackson, the library used by default with spring-boot for JSON serialization / deserialization.
And here is Spring blog post about it.

GsonFromJson: how to serialize and de serialize with array structures

Im working on a project where we used jsonfile as its database since SQLite doesnt meet the requirement. The project has a portion when an object fron the wordbank is use it will change the status(such as 1-4). I made use of JSONArray to access the data. When i tried to change/edit the status, it doesnt save or write back to the jsonfile. Instead it only works on the momentary use of the application.
From searches, alot of stuff pop out that using gson. I concluded to use gson.
I am new to gson and just started learning it the other day. And i am having troubles with it.
This is the structure of my jsonfile. It has 2 objects(users and wordbank) that are arrayed
{
"users" :
[{
"username": "free",
"password": "free",
"email": "free#gmail.com",
"type": "1"
},
{
"username": "premium",
"password": "premium",
"email": "premium#gmail.com",
"type": "2"
}],
"wordbank" :
[{
"English": "able",
"Cebuano": "kaya",
"Pronunciation": "ká-ya",
"POS": "adjective",
"Audio": "kaya.mp3",
"Status": "0"
},
{
"English": "advice",
"Cebuano": "tambag",
"Pronunciation": "tam-bag",
"POS": "noun",
"Audio": "tambag.mp3",
"Status": "0"
}]
}
From what I've seen in tutorial videos is that you create a different java class for its model. So i create 3 java class. user, wordbank and dictionary (combining them both).
public class dictionary{
users[] user;
wordbanks[] word;
}
Im using an existing jsonfile already so i parsed it and got its jsonstring. After which i tried to deserialize it using
jsonstring = readFromFile();//returns string from jsonfile
dictionary list = new Gson().fromJson(jsonstring, dictionary.class);
runned it and debug it. but when i got the results. it was null.
QUESTIONS:
1.Will I be able to edit and save the changes in json file by using gson?
2.Is my structure correct for the distionary class?
3.how to serialize and deserialize it?

If your member variables of pojo Classes(users,workdbank,dictionary) don't match with JSON key, consider using #SerializedName provided by GSON. In your case, i was able to deserialise the string using gson by using #SerializedName as shown below
User Class
public class User {
#SerializedName("username")
private String userName;
#SerializedName("password")
private String password;
#SerializedName("email")
private String email;
#SerializedName("type")
private String type;
// Add Getters and Setters
}
WordBank Class
public class Wordbank {
#SerializedName("English")
private String english;
#SerializedName("Cebuano")
private String cebuano;
#SerializedName("Pronunciation")
private String pronunciation;
#SerializedName("POS")
private String pos;
#SerializedName("Audio")
private String audio;
#SerializedName("Status")
private String status;
// Add getters and Setters
}
Dictionary Class
public class Dictonary {
#SerializedName("users")
User[] userArray;
#SerializedName("wordbank")
Wordbank[] wordbankArray;
public User[] getUserArray() {
return userArray;
}
public void setUserArray(User[] userArray) {
this.userArray = userArray;
}
public Wordbank[] getWordbankArray() {
return wordbankArray;
}
public void setWordbankArray(Wordbank[] wordbankArray) {
this.wordbankArray = wordbankArray;
}
}
After making necessary changes as explained above, I was able to deserialise the string
Dictonary dictonary = new Gson().fromJson(input,Dictonary.class);

Yes you can use Gson for all your requirements. First create matching Pojo for your json structure. you can use tools such as this pojo generator. Just paste the json there (don't select json schema) and generate. Assuming you have three classes Result (contains to lists, similar to your dictionary class), User and Wordbank class. You can read (deserialize) and write (serialize) back into a file as follows.
try {
// deserialize
Result result = gson.fromJson(new FileReader(new File("src/test/resources/sample.json")), Result.class);
// ... update result as required
// result.users.remove(0);
// serialize
String json = gson.toJson(result);
Files.write(new File("src/test/resources/sample.json").toPath(), json.getBytes());
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

Deserializing inner class with gson returns null

I want to use Gson to Deserialize my JSON into objects.
I've defined the appropriate classes, and some of those class' objects are included in other objects.
When trying to deserialize the whole JSON, I got null values, so I started breaking it apart.
I reached the point where all lower classes stand by them selves, but when trying to deserialize into an object that holds an instance of that smaller object - every thing returns as null.
My partial JSON:
{
"user_profile": {
"pk": 1,
"model": "vcb.userprofile",
"fields": {
"photo": "images/users/Screen_Shot_2013-03-18_at_5.24.13_PM.png",
"facebook_url": "https://google.com/facebook",
"site_name": "simple food",
"user": {
"pk": 1,
"model": "auth.user",
"fields": {
"first_name": "blue",
"last_name": "bla"
}
},
"site_url": "https://google.com/"
}
}
}
UserProfile Class:
public class UserProfile {
private int pk;
private String model;
private UPfields fields = new UPfields();//i tried with and without the "new"
}
UPfields Class:
public class UPfields {
private String photo;
private String facebook_url;
private String site_name;
private User user;
private String site_url;
}
User Class:
public class User {
private int pk;
private String model;
private Ufields fields;
}
Ufields Class:
public class Ufields {
private String first_name;
private String last_name;
}
In my main I call:
Gson gson = new Gson();
UserProfile temp = gson.fromJson(json, UserProfile.class);
So my temp object contain only null values.
I've tried changing the classes to static, and it doesn't work.
The UPfields object and all lower one work fine.
Any suggestions?
when I remove the
"{
"user_profile":"
and it's closing bracket, the deserialize to a user_profile object works.

In order to parse this json example you have to create auxiliary class, which will contain field named user_profile of type UserProfile:
public class UserProfileWrapper {
private UserProfile user_profile;
}
and parse this json string with this class:
UserProfileWrapper temp = gson.fromJson(json, UserProfileWrapper.class);

Gson starts by parsing the outermost object, which in your case has a single field, user_profile. Your UserProfile class doesn't have a user_profile field, so it can't deserialize it as an instance of that class. You should try to deserialize the value of the user_profile field instead.

How to convert Json String with dynamic fields to Object?

I have the followed snipets of Json String:
{
"networks": {
"tech11": {
"id": "1",
"name": "IDEN"
},
"tech12": {
"id": "2",
"name": "EVDO_B"
}
}
}
I use some methods to convert this String to Object:
private static Gson mGson = new Gson();
...
public static WebObjectResponse convertJsonToObject(String jsonString) {
WebObjectResponse webObjectResponse = null;
if(jsonString != null && jsonString.length() > 1){
webObjectResponse = mGson.fromJson(jsonString, WebObjectResponse.class);
}
return webObjectResponse;
}
Where WebObjectResponse is class that should represent above mentioned String.
Its not complicated if I get static fields.
But in my case the values have different names: tech11, tech12 ....
I can use #SerializedName but its works in specific cases like convert "class" to "class_".
As you see networks Object defined as list of tech Objects but with different post-fix.
public class WebObjectResponse{
private DataInfoList networks = null;
}
This is static implementation, i defined 2 values tech11 and tech12 but next response might be techXX
public class DataInfoList {
private DataInfo tech11 = null;
private DataInfo tech12 = null;
}
public class DataInfo {
private String id = null;
private String name = null;
}
What is the good way to convert current Json String to Object where list of elements are Objects too and have different names?
Thank you.

Use a Map!
I would do the following
public class WebObjectResponse {
private Map<String, DataInfo> networks;
}
public class DataInfo {
private String id = null;
private String name = null;
}
// later
Gson gson = new Gson();
String json = "{\"networks\": {\"tech11\": { \"id\": \"1\",\"name\": \"IDEN\" }, \"tech12\": { \"id\": \"2\", \"name\": \"EVDO_B\" } }}";
WebObjectResponse response = gson.fromJson(json, WebObjectResponse .class);
For each object in json networks, a new entry will be added to the Map field of your class WebObjectResponse. You then reference them by techXX or iterate through the keyset.
Assuming a structure like this
{
"networks": {
"tech11": {
"id": "1",
"name": "IDEN"
},
"tech12": {
"id": "2",
"name": "EVDO_B"
},
"tech13": {
"id": "3",
"name": "WOHOO"
}, ...
}
}

We would need your class structure for more details.
As far as I am aware, I think you will need to have some mappings defined somewhere (I used xml's) and then try to match json with one of the mappings to create objects.
Google gson is good. I did it in Jackson
Also, converting objects should be trivial. But since you might have variable fields like tech11 and tech12 , you might want to store the "network" value as a string and then extract fields out of it when required.
Hope I could help.
Edit : Sotirious nails it.

Please use this link for converting SON Response to Java POJO class
http://www.jsonschema2pojo.org/

What is the data structure of this JSON?

I'm trying to parse Json to Java by using Gson, but when I use fromJson(), I always get null. Who can explain this data structure for me? Thanks!
{
"d": {
"results": [
{
"__metadata": {
"uri": "https://api.datamarket.azure.com/Data.ashx/Bing/SearchWeb/v1/Web?Query='bill'gates'&$skip=0&$top=1",
"type": "WebResult"
},
"ID": "9bd0942f-fe5b-44fc-8343-ef85e5b93a7e",
"Title": "The Official Site of Bill Gates - The Gates Notes",
"Description": "In the space between business and goverment, even a small investment can make a big impact on the lives of those in need.",
"DisplayUrl": "www.thegatesnotes.com",
"Url": "http://www.thegatesnotes.com/"
},
{
"__metadata": {
"uri": "https://api.datamarket.azure.com/Data.ashx/Bing/SearchWeb/v1/Web?Query='bill'gates'&$skip=1&$top=1",
"type": "WebResult"
},
"ID": "fdf0d3b9-b29f-43ef-b5ba-6bb4b1b04458",
"Title": "Bill Gates - Wikipedia, the free encyclopedia",
"Description": "William Henry \"Bill\" Gates III (born October 28, 1955) is an American business magnate and philanthropist. Gates is the former chief executive and current chairman of ...",
"DisplayUrl": "en.wikipedia.org/wiki/Bill_Gates",
"Url": "http://en.wikipedia.org/wiki/Bill_Gates"
}
],
"__next": "https://api.datamarket.azure.com/Data.ashx/Bing/SearchWeb/v1/Web?Query='bill'gates'&$skip=10&$top=10"
}
}
I think the data structure should be like this, but it doesn't work.
public class d {
public result[] results;
public String __next;}
public class result {
public information[] infolist;}
public class information {
public __metadata metadata;
public String ID;
public String Title;
public String Description;
public String DisplayUrl;
public String Url;}
public class __metadata {
public String uri;
public String type;}

Your Information class is the problem. Put the Information stuff into Result and remove the infolist from Result. Also, the field name for the meta data is __metadata. This isn't the class name. Lastly, you're missing a class to wrap d as a field.
public class DataContainer {
public Data d;
}
public class Data {
public Result[] results;
public String __next;
}
public class Result {
public Metadata __metadata;
public String ID;
public String Title;
public String Description;
public String DisplayUrl;
public String Url;
}
public class Metadata {
public String uri;
public String type;
}
You really should use common convention for class names. Gson won't preclude you from using your own names for classes. It only requires control for the name of the fields.
To deserialize:
String json = ... ;
DataContainer myDataContainer = new Gson().fromJson(JSONString , DataContainer.class);
Result[] myResult = myDataContainer.d.results;
Try that and see if that works.
Here's how you should interpret the JSON when you're writing a class structure around it for Gson:
An opening { indicates an object, so this will be a new class (or an existing one if they have the same fields)
A "this": indicates a field for the object it's inside, and the field must be named the same thing as the text in the string.
An opening [ indicates an array, a List, or a Set (Result[] results could just as easily be List<Result> results)