Cannot convert JSON response into Java object using JSON

Cannot convert JSON response into Java object using JSON - java

I am trying to convert the http response body which is in JSON format into a Java object using the GSON library, but the object has all attributes equal to null after trying to do so.
My Object class:
public class User {
private String username;
private int shipCount;
private int structureCount;
private String joinedAt;
private int credits;
public User(String username, int shipCount, int structureCount, String joinedAt, int credits) {
this.username = username;
this.shipCount = shipCount;
this.structureCount = structureCount;
this.joinedAt = joinedAt;
this.credits = credits;
}
Plus getters and setters
My attempt at using GSON:
Gson gso = new Gson();
User userInf = gso.fromJson(response.body(), User.class);
System.out.println(userInf);
The response body is this:
{"user":{"username":":chrter","shipCount":0,"structureCount":0,"joinedAt":"2022-04-09T16:52:14.365Z","credits":0}}
Any help is greatly appreciated

The root object of your HTTP response is a JSON object that has only one field - "user". When GSON deserializes the response, it goes through all the fields of the root object and sets them to the corresponding fields of the class you have provided. So it will look for the field user in the class User and set it to the JSON's data.
Since class User has no field user, GSON doesn't fill that field. In fact it doesn't fill out any other fields, because there are no other fields in the root object.
To get around this you need to deserialize not the whole response, but only the user field of the root object. There are two ways of doing that.
Deserialize the root object, and then deserialize the field user of that object into the User class.
You can find an example of how to do it in #Saheed's answer. However you should note that it translates JSON string into java objects and then translates java objects back. It might cost you additional time if you're doing it in performance-sensitive area of your program.
Create another class which you will deserialize into, which would have the field user. It looks like this:
class Response {
public User user;
};
class User {
// ...
};
And then you deserialize like this:
Gson gso = new Gson();
// CHANGE: Deserialize the response and get the user field
Response response = gso.fromJson(response.body(),Response.class);
User userInf = response.user;
System.out.println(userInf);

Try something like this:
public static Map<String, Object> Converter(String str){
Map<String, Object> map = new Gson().fromJson(str, new TypeToken<HashMap<String, Object>>() {}.getType());
return map;
}
Map<String, Object> apiResponse = Converter(response.body().toString());
Map<String, Object> username = Converter(apiResponse.get("user").toString());
System.out.println(username);
Tweak it a bit to suit your need

Try this.
Map<?, ?> map = gson.fromJson(response.body(), Map.class);
for (Map.Entry<?, ?> entry : map.entrySet()) {
System.out.println(entry.getKey() + "=" + entry.getValue());
}

Related

Need to manipulate returned JSON Object and extract a portion to a List

I'm consuming an external API, for which a JSON Object is returned. Contained in that Object response is an array that I need to extract and set to a List of a particular entity type. Java, however, is not a language that I'm very familiar with, so I'm having problems attempting to figure this out.
I've created a type of wrapper class to work with this in the setter.
The best I've come up with that compiles is below, but produces an error that I can't figure out.
public void setFlights(Object responseBody) {
String responseString = responseBody.toString();
JSONObject responseJSONObject = new JSONObject(responseString);
JSONArray responseJSONArray = responseJSONObject.getJSONArray("flights");
Gson gson = new Gson();
Type flightType = new TypeToken<List<Flight>>() {}.getType();
this.flights = gson.fromJson(String.valueOf(responseJSONArray), flightType);
}
As you can see, I'm kind of throwing it at the wall to see if it will stick. I'm trying to use Gson to get around some of the Type issues I've come across.
The error produced when executing is:
org.json.JSONException: Expected a ':' after a key at 7 [character 8 line 1]
Response String is as follows:
Response String Image
If that's difficult to deal with, here's the response in text:
INFO: {"FlightInfoResult":{"next_offset":-1,"flights":[{"ident":"N1RJ","aircrafttype":"HDJT","filed_ete":"01:25:00","filed_time":1593038253,"filed_departuretime":1593037500,"filed_airspeed_kts":400,"filed_airspeed_mach":"","filed_altitude":360,"route":"WEAZL4 CLAWD","actualdeparturetime":1593038285,"estimatedarrivaltime":1593043320,"actualarrivaltime":1593043320,"diverted":"","origin":"KJQF","destination":"KJXN","originName":"Concord-Padgett Rgnl","originCity":"Concord, NC","destinationName":"Jackson County","destinationCity":"Jackson, MI"},{"ident":"N1RJ","aircrafttype":"HDJT","filed_ete":"01:24:00","filed_time":1593000320,"filed_departuretime":1592998200,"filed_airspeed_kts":400,"filed_airspeed_mach":"","filed_altitude":350,"route":"PEGTE","actualdeparturetime":1593000420,"estimatedarrivaltime":1593005149,"actualarrivaltime":1593005149,"diverted":"","origin":"KJXN","destination":"KJQF","originName":"Jackson County","originCity":"Jackson, MI","destinationName":"Concord-Padgett Rgnl","destinationCity":"Concord, NC"},{"ident":"N1RJ","aircrafttype":"HDJT","filed_ete":"01:29:00","filed_time":1592518049,"filed_departuretime":1592513400,"filed_airspeed_kts":317,"filed_airspeed_mach":"","filed_altitude":360,"route":"WEAZL4 CLAWD","actualdeparturetime":1592517936,"estimatedarrivaltime":1592523120,"actualarrivaltime":1592523120,"diverted":"","origin":"KJQF","destination":"KJXN","originName":"Concord-Padgett Rgnl","originCity":"Concord, NC","destinationName":"Jackson County","destinationCity":"Jackson, MI"},{"ident":"N1RJ","aircrafttype":"HDJT","filed_ete":"01:24:00","filed_time":1592481020,"filed_departuretime":1592479800,"filed_airspeed_kts":319,"filed_airspeed_mach":"","filed_altitude":350,"route":"PEGTE","actualdeparturetime":1592481126,"estimatedarrivaltime":1592486100,"actualarrivaltime":1592486100,"diverted":"","origin":"KJXN","destination":"KJQF","originName":"Jackson County","originCity":"Jackson, MI","destinationName":"Concord-Padgett Rgnl","destinationCity":"Concord, NC"}]}}
There very well may be a much more simple way of accomplishing what I need. Any example help is very much appreciated.

You can use Gson string to object mapper class directly as like below,
package com.sample.programs;
import java.util.List;
import com.google.gson.Gson;
public class FlightInfoResultMain {
public static void main(String[] args) {
String input = "{\"FlightInfoResult\":{\"next_offset\":-1,\"flights\":[{\"ident\":\"N1RJ\",\"aircrafttype\":\"HDJT\",\"filed_ete\":\"01:25:00\",\"filed_time\":1593038253,\"filed_departuretime\":1593037500,\"filed_airspeed_kts\":400,\"filed_airspeed_mach\":\"\",\"filed_altitude\":360,\"route\":\"WEAZL4 CLAWD\",\"actualdeparturetime\":1593038285,\"estimatedarrivaltime\":1593043320,\"actualarrivaltime\":1593043320,\"diverted\":\"\",\"origin\":\"KJQF\",\"destination\":\"KJXN\",\"originName\":\"Concord-Padgett Rgnl\",\"originCity\":\"Concord, NC\",\"destinationName\":\"Jackson County\",\"destinationCity\":\"Jackson, MI\"},{\"ident\":\"N1RJ\",\"aircrafttype\":\"HDJT\",\"filed_ete\":\"01:24:00\",\"filed_time\":1593000320,\"filed_departuretime\":1592998200,\"filed_airspeed_kts\":400,\"filed_airspeed_mach\":\"\",\"filed_altitude\":350,\"route\":\"PEGTE\",\"actualdeparturetime\":1593000420,\"estimatedarrivaltime\":1593005149,\"actualarrivaltime\":1593005149,\"diverted\":\"\",\"origin\":\"KJXN\",\"destination\":\"KJQF\",\"originName\":\"Jackson County\",\"originCity\":\"Jackson, MI\",\"destinationName\":\"Concord-Padgett Rgnl\",\"destinationCity\":\"Concord, NC\"},{\"ident\":\"N1RJ\",\"aircrafttype\":\"HDJT\",\"filed_ete\":\"01:29:00\",\"filed_time\":1592518049,\"filed_departuretime\":1592513400,\"filed_airspeed_kts\":317,\"filed_airspeed_mach\":\"\",\"filed_altitude\":360,\"route\":\"WEAZL4 CLAWD\",\"actualdeparturetime\":1592517936,\"estimatedarrivaltime\":1592523120,\"actualarrivaltime\":1592523120,\"diverted\":\"\",\"origin\":\"KJQF\",\"destination\":\"KJXN\",\"originName\":\"Concord-Padgett Rgnl\",\"originCity\":\"Concord, NC\",\"destinationName\":\"Jackson County\",\"destinationCity\":\"Jackson, MI\"},{\"ident\":\"N1RJ\",\"aircrafttype\":\"HDJT\",\"filed_ete\":\"01:24:00\",\"filed_time\":1592481020,\"filed_departuretime\":1592479800,\"filed_airspeed_kts\":319,\"filed_airspeed_mach\":\"\",\"filed_altitude\":350,\"route\":\"PEGTE\",\"actualdeparturetime\":1592481126,\"estimatedarrivaltime\":1592486100,\"actualarrivaltime\":1592486100,\"diverted\":\"\",\"origin\":\"KJXN\",\"destination\":\"KJQF\",\"originName\":\"Jackson County\",\"originCity\":\"Jackson, MI\",\"destinationName\":\"Concord-Padgett Rgnl\",\"destinationCity\":\"Concord, NC\"}]}}";
System.out.println("input - " + input);
//Create Gson object
Gson gson = new Gson();
FlightInfoResultObject responseObject = gson.fromJson(input, FlightInfoResultObject.class);
// parsing response to java pojo
List<Flights> listOfFlights = responseObject.getFlightInfoResult().getFlights();
for (Flights flight : listOfFlights) {
System.out.println("flight - " + flight.getIdent());
}
}
}
Object Mapping class: Inside Flights.class you can add all the variable which you have in json response.
class FlightInfoResultObject {
FlightInfoResult FlightInfoResult;
#Getter
#Setter
}
class FlightInfoResult {
Integer next_offset;
List<Flights> flights;
#Getter
#Setter
}
class Flights {
String ident;
String aircrafttype;
#Getter
#Setter
}

I think it's impossible to retrieve the inner JSON element directly using gson.
You have to get FlightInfoResult then flights accordingly. This should work:
Gson gson = new Gson();
JsonObject jsonObject = com.google.gson.JsonParser.parseString(responseString).getAsJsonObject();
JsonArray flightArray = jsonObject.getAsJsonObject("FlightInfoResult").getAsJsonArray("flights");
Type flightType = new TypeToken<List<Flight>>() {}.getType();
List<Flight> flights = gson.fromJson(flightArray, flightType);
Anyway, make sure the name of all properties inside class Flight matches Json elements name, to avoid mapping errors.
Since you didn't post your Flight class definition and gson naming rule, but the Flight class should be like:
public class Flight {
private String ident;
private String aircrafttype;
private String filed_ete;
private float filed_time;
private float filed_departuretime;
private float filed_airspeed_kts;
private String filed_airspeed_mach;
private float filed_altitude;
private String route;
private float actualdeparturetime;
private float estimatedarrivaltime;
private float actualarrivaltime;
private String diverted;
private String origin;
private String destination;
private String originName;
private String originCity;
private String destinationName;
private String destinationCity;
// getters setters

java convert map into a pojo when attribute names are different

Is it possible to convert map into a pojo when attribute names are different?
I am extracting raw input into a map to have the following data. Data can vary based on message type. For example:
for Message type = STANDARD
Map<String, Double> data = new HashMap<>();
data.set('TEMP', 18.33);
data.set('BTNUM', 123);
for Message type = NON_STANDARD
Map<String, Double> data = new HashMap<>();
data.set('GPSLAT', 12.33);
data.set('GPSLON', 42.33);
For each message type I have a Java model class
#Data
public class StandardMessage {
private String longitude;
private String latitude;
}
#Data
public class NonStandardMessage {
private String temperature;
private String btNumber;
}
Currenly I am mapping data to POJO class manually like below
StandardMessage sm = new StandardMessage();
sm.setLongitude(data.get('GPSLON'));
NonStandardMessage nsm = new NonStandardMessage();
nsm.setTemperature(data.get('TEMP'));
Is it possible to make above mapping generic? i.e setting object property without knowing name?
In Typescript we can achieve this easily by defining configuration like:
objectPropertyMapping = new Map();
objectPropertyMapping.set('GPSLAT', 'latitude');
objectPropertyMapping.set('GPSLON', 'longitude');
standardMessage = {};
data.forEach((value: boolean, key: string) => {
standardMessage[ObjectPropertyMapping.get(key)] = data[key];
});
https://stackblitz.com/edit/angular-zjn1kc?file=src%2Fapp%2Fapp.component.ts
I know Java is a statically-typed language, just wondering is there a way to achieve this like typescript or we have to map manually all the time?

We use jackson-databind. It uses annotations for configuration.
Here are some example:
The entity class:
class MessageRequest {
#JsonProperty("A")
private String title;
#JsonProperty("B")
private String body;
... getters and setters ...
}
The main method:
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
Map<String, Object> source = new HashMap<>();
source.put("A", "This is the title");
source.put("B", "Here is the body");
MessageRequest req = objectMapper.convertValue(source, MessageRequest.class);
System.out.println(req.getTitle());
System.out.println(req.getBody());
}

Create JSON String using GSON

I am having a class like following,
public class Student {
public int id;
public String name;
public int age;
}
Now I want to create new Student,
//while create new student
Student stu = new Student();
stu.age = 25;
stu.name = "Guna";
System.out.println(new Gson().toJson(stu));
This gives me the following output,
{"id":0,"name":"Guna","age":25} //Here I want string without id, So this is wrong
So here I want String like
{"name":"Guna","age":25}
If I want to edit old Student
//While edit old student
Student stu2 = new Student();
stu2.id = 1002;
stu2.age = 25;
stu2.name = "Guna";
System.out.println(new Gson().toJson(stu2));
Now the output is
{"id":1002,"name":"Guna","age":25} //Here I want the String with Id, So this is correct
How can I make a JSON String with a field [At some point], without a field [at some point].
Any help will be highly appreciable.
Thanks.

Better is to use #expose annotation like
public class Student {
public int id;
#Expose
public String name;
#Expose
public int age;
}
And use below method to get Json string from your object
private String getJsonString(Student student) {
// Before converting to GSON check value of id
Gson gson = null;
if (student.id == 0) {
gson = new GsonBuilder()
.excludeFieldsWithoutExposeAnnotation()
.create();
} else {
gson = new Gson();
}
return gson.toJson(student);
}
It will ignore id column if that is set to 0, either it will return json string with id field.

You can explore the json tree with gson.
Try something like this :
gson.toJsonTree(stu1).getAsJsonObject().remove("id");
You can add some properties also :
gson.toJsonTree(stu2).getAsJsonObject().addProperty("id", "100");

JsonObject jsObj = (JsonObject) new Gson().toJsonTree(stu2);
jsObj.remove("age"); // remove field 'age'
jsObj.addProperty("key", "value"); // add field 'key'
System.out.println(jsObj);
You can manipulate with JsonObject

You should introduce additional field to Student class that will notice GSON about id serialization policy.
Then, you should implement custom serializer that will implement TypeAdapter. In your TypeAdapter implementation according to id serialization policy you will serialize it or not. Then you should register your TypeAdapter in GSON factory:
GsonBuilder gson = new GsonBuilder();
gson.registerTypeAdapter(Student.class, new StudentTypeAdapter());
Hope this helps.

You have two options.
Use Java's transient keyword which is to indicate that a field should not be serialized. Gson will exclude it automatically. This may not work for you as you want it conditionally.
Use #Expose annotation for the fields that you want and initialize your Gson builder as following:
Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
So you need to mark name and age fields using #Expose and you need to have two different Gson instances for the default one which includes all fields and the one above which excludes fields without #Expose annotation.

Gson to json add map dynamically to object

I have an object that represents an event that I would like to serialize into json, using gson or another library if that works easier.
I want to add the following type of field to the json:
private Map<String, String> additionalProperties;
And also in another use case:
private Map<String, Object> additionalProperties;
But if I add additionalProperties to the Event object, and build Gson in the normal way:
Gson gson = BUILDER.create();
String json = gson.toJson(event);
It will appear like so:
additional_properties: {"value1":1,"value2":"abc"}
I would simply like to append to the event object in the following form:
{"value1":1,"value2":"abc"}
Here is an example output- the additional properties added are the object 'z' and the object 'advertiser':
{"organisationid":"2345612ß","projectid":"12345678",
"place":{"placeId":"2345","last_place":"123-3"},
"advertiser":{"advertiserId":"2345a","code":"a123-3"},
"user":{"isY":false,"isHere":false,"isBuyer":false},
"x":{"identifier":"SHDG-28CHD"},
"z":{"identifier":"abcSHDG-28CHD"},
"event_type":"x_depart"}
Here is what it currently looks like:
{"organisationid":"2345612ß","projectid":"12345678",
"place":{"placeId":"2345","last_place":"123-3"},
additionalproperty: {"advertiser":{"advertiserId":"2345a","code":"a123-3"},
"user":{"isY":false,"isHere":false,"isBuyer":false},
"x":{"identifier":"SHDG-28CHD"},
additionalproperty: {"z":{"identifier":"abcSHDG-28CHD"}},
"event_type":"x_depart"}

The best way to solve this would be with a framework for adding properties dynamically, but without this, you could add the additional properties to your Event object (include #JsonIgnore
so that it is not part of the final json), create a new JSONObject from the additional properties and merge it to the event JSONObject before serializing to json. This way the additional properties are added dynamically to the resulting Event output.
In the Event class:
#JsonIgnore
private Map<String, Object> additionalProperties;
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}
public void setAdditionalProperties(Map<String, Object> additionalProperties) {
this.additionalProperties = additionalProperties;
}
A function to merge two JSONObjects:
public static JSONObject mergeObjects(JSONObject source, JSONObject target) throws JSONException {
for (String key: JSONObject.getNames(source)) {
Object value = source.get(key);
if (!target.has(key)) {
// new value for "key":
target.put(key, value);
} else {
// existing value for "key" - recursively deep merge:
if (value instanceof JSONObject) {
JSONObject valueJson = (JSONObject)value;
deepMerge(valueJson, target.getJSONObject(key));
} else {
target.put(key, value);
}
}
}
return target;
}
Putting the two objects together:
String jsonAdd = mapper.writeValueAsString(additional);
String jsonEvent = mapper.writeValueAsString(event);
JSONObject jsonAddObj = new JSONObject(jsonAdd);
JSONObject JsonEventObj = new JSONObject(jsonEvent);
JSONObject finalJson = Merge.deepMerge(jsonAddObj, JsonEventObj);

If your Event class is something like;
class Event {
private Map<String, Object> additionalProperties;
}
and you are calling;
String json = gson.toJson(event);
The ecpected and the valid output would be:
{"additionalProperties":{"value1":1,"value2":"abc"}}
If you want an output such as;
{"value1":1,"value2":"abc"}
You can call;
String json = gson.toJson(event.additionalProperties);
I would simply like to append to the event object in the following
form:
{"value1":1,"value2":"abc"}
That way it won't be a valid json variable if you append that value directly to a json object. You should better try if the json value you want is valid or not at http://jsonviewer.stack.hu/

Json Data assign to java class

I'm having problem to assign json data into java class.Please do help anyone,
My java class is like,
public class ListofGridRecords<T> {
public int Totalrecords;
public List<T> GridRecords;//using TraderTransaction class.
}
and TraderTransaction class is,
public class TraderTransaction {
public Date AddedTime;
public String TransactId;
public TransactStatus Status;
public String OtherPartyAccountNo;
public Double AmountPaid;
public Double AmountRecieved;
public Double ClosingBalance;
public TransactionTypes TransType;
public String Narration;
public TraderTransaction() {
super();
}
}
and my json conversion function look like,
JsonObject returndata = JsonObject.parse(responseString);
String operationresult = returndata.get("OperationResult").toString();
if (Result.values()[Integer.parseInt(operationresult)] == Result.Success) {
Gson gson = new Gson();
#SuppressWarnings("unchecked")
ListofGridRecords<TraderTransaction> traderlist =
gson.fromJson(returndata.get("ResultData").toString(), ListofGridRecords.class);
Log.i("LIST DATA:", "" + traderlist);
for (TraderTransaction trader: traderlist.GridRecords) {
HashMap<String, String> map = new HashMap<String, String>();
map.put(TRANS_FIRST_COLUMN, currentformatter.format(trader.AddedTime));
map.put(TRANS_SECOND_COLUMN, trader.TransactId);
map.put(TRANS_THIRD_COLUMN, trader.OtherPartyAccountNo);
map.put(TRANS_FOURTH_COLUMN, trader.AmountPaid.toString());
map.put(TRANS_FIFTH_COLUMN, trader.AmountRecieved.toString());
map.put(TRANS_SIXTH_COLUMN, OpenOrClosed.values()[Integer.parseInt(trader.TransType.toString())].toString());
list.add(map);
}
}
I'm getting conversion error at for (TraderTransaction trader : traderlist.GridRecords).
My Json data look like,
{
"Messages":"RESULTS_RETRIEVAL_SUCCESSFULL",
"OperationResult":0,
"ResultData":{
"GridRecords":[
{
"AddedBy":"Distributor-9787457361-Rathinavel",
"AddedTime":"2013-04-12T16:26:24.0140117",
"AmountPaid":0.0,
"AmountRecieved":10000.0,
"ClosingBalance":10000.0,
"Narration":null,
"OtherPartyAccountNo":"0102849015327675",
"Status":2,
"TransType":2,
"TransactId":"TDRF483679051236"
},
{
"AddedBy":"Distributor-9787457361-Rathinavel",
"AddedTime":"2013-04-12T16:20:54.8681857",
"AmountPaid":0.0,
"AmountRecieved":0.0,
"ClosingBalance":0.0,
"Narration":null,
"OtherPartyAccountNo":"0102849015327675",
"Status":0,
"TransType":2,
"TransactId":"TDRF706925413802"
}
],
"Totalrecords":2
},
"UpdateAvailable":"0"
}

In order to parse your JSON, I'd use a slightly different strategy. As you seem to be interested in parsing only the "ResultData", I'd create classes to wrap the response, very similar to those you have already created, namely:
public class Response {
#SerializedName("ResultData")
public ResultData resultData;
}
and,
public class ResultData {
#SerializedName("GridRecords")
public List<GridRecord> gridRecords;
#SerializedName("Totalrecords")
public int totalrecords;
}
and,
public class GridRecord {
#SerializedName("AddedTime")
public String addedTime;
#SerializedName("TransactId")
public String transactId;
//other fields...
}
and other classes if necessary...
Then, in order to parse your JSON reponse, you just have to do:
Gson gson = new Gson();
Response data = gson.fromJson(responseString, Response.class);
and you'll be able to access any field, for example:
data.resultData.gridRecords.transactId;
Note 1: If you are interested in more fields of the JSON response, you just have to add more fields to your wrap classes, according to the JSON response...
Note 2: I've changed the type of addedTime to String, instead of Date because it throws an exception for unparseable date. Anyway I usually leave the types in the Response objects as simple String and then in the class from where I retrieve the response, I do the correct formatting while creating my objects, for example, when you put the values in your Map...
Note 3: The use of the annotation #SerializedName is interesting to separate the name of a field in the JSON response and in your app, in order to follow Java naming conventions, which your attributes are not following...
Note 4: You shouldn't use public attributes in your classes. It's more recommendable to use private/protected attributes and their correspondent getters and setters...

Develop Reference

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Cannot convert JSON response into Java object using JSON - java

Try this. Map<?, ?> map = gson.fromJson(response.body(), Map.class); for (Map.Entry<?, ?> entry : map.entrySet()) { System.out.println(entry.getKey() + "=" + entry.getValue()); }

Related

Need to manipulate returned JSON Object and extract a portion to a List

java convert map into a pojo when attribute names are different

Create JSON String using GSON

Gson to json add map dynamically to object

Json Data assign to java class

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