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How to convert JSON to Java object if I do not know all json fields before parsing?

My service can receive several different jsons, such as:
{
"event":"conversation_started",
"context":"context information",
"user":{
"id":"01234567890A=",
"name":"John McClane",
"avatar":"http://avatar.example.com",
"country":"UK",
"language":"en",
"api_version":1
},
"subscribed":false
}
or
{
"event":"message",
"message":{
"type":"text",
"text":"a message to the service",
"location":{
"lat":12.34,
"lon":12.34
}
}
}
or several else jsons. The only field that is the same for all jsons is "event". All other fields can be different (depends on "event" value).
So the question is: how to convert those jsons to java objects (without making messy code)? The only way I know is to manually check "event" value (like json.startsWith("{\n\"event\":\"message\"") but I'm sure that there is any simple decision for doing this.

There are three ways I've done this. The first is to do what you're suggesting - parse the JSON, check the type, and create the object. Be very careful with using a String parser as you may or may not have things like new lines. Instead, do something like:
ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readTree(eventString);
String eventType = jsonNode.get("event").asText();
if( eventType.equalsIgnoreCase("conversation_started")) {
// create ConversationStarted object using something like:
ConversationStarted conversationStarted = objectMapper.readValue( eventString, ConversationStarted.class );
}
This, of course, requires all classes to have a concrete POJO to allow for deserialization.
Another way is to do what many other programming languages do and have a key/value map. There are a few ways to do this. One is with the Jackson libraries:
Map<String, Object> map = objectMapper.readValue(eventString, new TypeReference<Map<String,Object>>(){});
Map<String, Object> user = (Map<String, Object>) map.get("user");
System.out.println( "conversation started - avatar is " + user.get("avatar"));
That way you can pass around the Map and extract as needed. Note that you still need to understand the structure of the JSON but you don't need to have a POJO for it.
Lastly is a variation on the second solution. Using JSONPath you can pull out what you need directly. Again you will want to first check out which type of event you have. Something like:
if( JsonPath.read(eventString, "$.event").equals("conversation_started") ) {
String avatar = JsonPath.read(eventString, "$.user.avatar");
System.out.println("conversation started - avatar is " + avatar);
}
The last two methods require you to pull out values one at a time as shown. The first solution gives you a full object to work with. It is your call as to what works best in your environment.

UPD: If you don't want to convert JSON String to JAVA Object via declaring a POJO, you can parse it to JSONObject(com.alibaba.fastjson.JSONObject)
public class Event {
public static void main(String[] args) {
String jsonA = "{\"event\":\"conversation_started\",\"context\":\"context information\",\"user\":{\"id\":\"01234567890A=\",\"name\":\"John McClane\",\"avatar\":\"http://avatar.example.com\",\"country\":\"UK\",\"language\":\"en\",\"api_version\":1},\"subscribed\":false}";
String jsonB = "{\"event\":\"message\",\"message\":{\"type\":\"text\",\"text\":\"a message to the service\",\"location\":{\"lat\":12.34,\"lon\":12.34}}}";
JSONObject jsonObject = JSONObject.parseObject(jsonA);
String event = jsonObject.getString("event");
if (event.equals("message")) {
//do what you want to do
System.out.println("message event......");
} else if ("conversation_started".equals(event)) {
System.out.println("context information event......");
}
}
}
Declaring a class of Event as below, and then convert JSON String to a Event JAVA object.
#Data
public class Event {
private String event;
private String context;
private User user;
private boolean subscribed;
private Message message;
#Data
public static class User {
private String id;
private String name;
private String avatar;
private String country;
private String language;
private int api_version;
}
#Data
public static class Message {
private String type;
private String text;
private Location location;
#Data
public static class Location {
private double lat;
private double lon;
}
}
public static void main(String[] args) {
String jsonA = "{\"event\":\"conversation_started\",\"context\":\"context information\",\"user\":{\"id\":\"01234567890A=\",\"name\":\"John McClane\",\"avatar\":\"http://avatar.example.com\",\"country\":\"UK\",\"language\":\"en\",\"api_version\":1},\"subscribed\":false}";
String jsonB = "{\"event\":\"message\",\"message\":{\"type\":\"text\",\"text\":\"a message to the service\",\"location\":{\"lat\":12.34,\"lon\":12.34}}}";
ObjectMapper objectMapper = new ObjectMapper();
try {
Event eventA = objectMapper.readValue(jsonA, new TypeReference<Event>() {
});
System.out.println(objectMapper.writeValueAsString(eventA));
Event eventB = objectMapper.readValue(jsonB, new TypeReference<Event>() {
});
System.out.println(objectMapper.writeValueAsString(eventB));
} catch (IOException e) {
e.printStackTrace();
}
}
}

Use a JSON object. This is dynamic and can load any json. Then you can reference the event field consistently
Example 1
//import java.util.ArrayList;
//import org.bson.Document;
Document root = Document.parse("{ \"event\" : \"conversation_started\", \"context\" : \"context information\", \"user\" : { \"id\" : \"01234567890A=\", \"name\" : \"John McClane\", \"avatar\" : \"http://avatar.example.com\", \"country\" : \"UK\", \"language\" : \"en\", \"api_version\" : 1 }, \"subscribed\" : false }");
System.out.println(((String)root.get("event")));
Example 2
//import java.util.ArrayList;
//import org.bson.Document;
Document root = Document.parse("{ \"event\" : \"message\", \"message\" : { \"type\" : \"text\", \"text\" : \"a message to the service\", \"location\" : { \"lat\" : 12.34, \"lon\" : 12.34 } } }");
System.out.println(((String)root.get("event")));

How to Parse Get Request Response to get All key and Value pairs?

I was able to pull data from an api using my get request method
{"vulnerabilities":[{"id":5027994,"status":"open","closed_at":null,"created_at":"2019-06-07T06:10:15Z","due_date":null,"notes":null,"port":[],"priority":null,"identifiers":["adobe-reader-apsb09-15-cve-2009-2990"],"last_seen_time":"2019-07-24T05:00:00.000Z","fix_id":4953,"scanner_vulnerabilities":[{"port":null,"external_unique_id":"adobe-reader-apsb09-15-cve-2009-2990","open":true}],"asset_id":119920,"connectors":[{"name":"Nexpose Enterprise","id":7,"connector_definition_name":"Nexpose Enterprise","vendor":"R7"}],"service_ticket":null,"urls":{"asset":"dummy.com"},"patch":true,"patch_published_at":"2009-10-08T22:40:52.000Z","cve_id":"CVE-2009-2990","cve_description":"Array index error in Adobe Reader and Acrobat 9.x before 9.2, 8.x before 8.1.7, and possibly 7.x through 7.1.4 might allow attackers to execute arbitrary code via unspecified vectors.","cve_published_at":"2009-10-19T22:30:00.000Z","description":null,"solution":null,"wasc_id":null,"severity":9,"threat":9,"popular_target":false,"active_internet_breach":true,"easily_exploitable":true,"malware_exploitable":true,"predicted_exploitable":false,"custom_fields":[],"first_found_on":"2019-06-05T05:22:23Z","top_priority":true,"risk_meter_score":100,"closed":false}
the problem I have encountered is to parse this json data by separating it by colon and comma?
I have created a parser method show below:
public static TableRow parseRequest(String request, TableRow row) {
JsonParser parser= new JsonParser();
try {
Object object = parser.parse(request);
//throws an ClassCastException JsonObject jsonObject = (JsonObject) object;
JsonArray array = (JsonArray) object;
for (Iterator iterator = jsonObject.keySet().iterator(); iterator.hasNext(); ) {
String keyString = (String) iterator.next();
System.out.println("iterator" + iterator);
System.out.println(jsonObject.get(keyString));
}
} catch (Exception e) {
e.printStackTrace();
// TODO: handle exception
}
return parserequesTableRow(row);
}
The results that I get is java.lang.ClassCastException. I am very new to Json so I would like to know if there is a better method than the one I am implementing?

I would advise to use jackson library for this. Jackson is a library for parsing json string to java class. You can also generate a json from a java class. See here for more info and how to use it: https://www.baeldung.com/jackson-object-mapper-tutorial
Here is an example how you can set it up. First create a java pojo which should be equal to your response json:
#JsonInclude(NON_NULL)
class Response {
private List<Vulnerability> vulnerabilities;
// getters and setters
}
#JsonInclude(NON_NULL)
class Vulnerability {
private String id;
private String status;
private String closed_at;
private String created_at;
private String due_date;
private String notes;
private String[] port;
private String priority;
// etc for other class members
// getters and setters
}
And here is your parsing logic:
public static void main(String[] args) throws IOException {
String json = ""; //put here your data which you got from your get request
ObjectMapper objectMapper = new ObjectMapper();
Response response = objectMapper.readValue(json, Response.class);
}

How to get and ignore specific field in JSON

Game class:
public class Game {
private String name;
private int steam_appid;
private boolean isInstalled;
}
Json example: https://store.steampowered.com/api/appdetails/?appids=435150&filters=basic
My attempt:
public static Game readJson(String gameID) throws IOException {
String targetURL = String.format(STEAM_API, gameID);
URL url = new URL(targetURL);
InputStreamReader reader = new InputStreamReader(url.openStream());
Gson gson = new Gson();
Game json = gson.fromJson(reader, Game.class);
return json;
}
When I tried to print the output, I get Name:null steam_appid:0 isInstalled:false
I want to check the key success first, if value is true parse it to Game. Otherwise, do nothing.
How can I parse the Json to my Game?

If a field is marked transient, (by default) it is ignored and not included in the JSON serialization or deserialization.
https://sites.google.com/site/gson/gson-user-guide#TOC-Finer-Points-with-Objects

use below code if you don't want to include name in json:
public class Game
{
private transient String name;
private int steam_appid;
private boolean isInstalled;
}

Option 1:
Ignore Field at the Field Level
public class Game {
private String name;
#JsonIgnore
private int steam_appid;
private boolean isInstalled;
}
We can also ignore a field directly via the #JsonIgnore annotation directly on the field:
Option 2:
In another way you can use #JsonIgnoreProperties annotation to skip pojo properties. Here is the code snippet: You can use either way.
#JsonIgnoreProperties({ "name", "steam_appid" })
public class Game {
private String name;
private int steam_appid;
private boolean isInstalled;
}

Based on the response example the class to use Gson should look like this:
Note the classes need the getters and setters to be added.
class SteamResponseWrapper{
#SerializedName("434150")
private SteamResponse steamResponse;
}
class SteamResponse{
boolean success;
GameData data;
}
class GameData {
String name;
int steam_appid;
// I couldn't find the isInstalled property if you are adding it, make it transient
}
With this structure you would call:
SteamResponseWrapper wrapper = new Gson().fromJson(reader, SteamResponseWrapper.class)
and then
wrapper.getSteamResponse().isSuccess()
to check the success field.
And
wrapper.getSteamResponse().getData()
to access the game object.
But the problem I see is that the top object name is in fact data and will change for every game. So I don't think Gson will be able to handle this because for every request the annotated serialized name should be different.
I think you will be better of handling it with Jackson or as a JsonObject.
EDIT I
This example uses these maven dependencies:
<dependency>
<groupId>javax.json</groupId>
<artifactId>javax.json-api</artifactId>
<version>1.0</version>
</dependency>
<dependency>
<groupId>org.glassfish</groupId>
<artifactId>javax.json</artifactId>
<version>1.0.4</version>
</dependency>
The example:
public class SteamApiReader {
private static final String STEAM_API = "http:// ......";
public static void main(String args[]) {
try {
SteamApiReader.readJson("435150");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static Game readJson(String gameID) throws IOException {
Game rtn = null;
String targetURL = String.format(STEAM_API, gameID);;
URL url = new URL(targetURL);
InputStreamReader reader = new InputStreamReader(url.openStream());
JsonReader jsonReader = Json.createReader(reader);
JsonStructure jsonStructure = jsonReader.read();
JsonObject jsonObject = (JsonObject) jsonStructure;
JsonObject wrapper = jsonObject.getJsonObject(gameID);
boolean success = wrapper.getBoolean("success");
if(success) {
JsonObject data = wrapper.getJsonObject("data");
String name = data.getString("name");
int steamAppId = data.getInt("steam_appid");
rtn = new Game(name, steamAppId);
}
return rtn;
}
public static class Game{
public Game(String name, int steamAppId) {
this.name = name;
this.steamAppId = steamAppId;
}
String name;
int steamAppId;
}
}

Can not deserialize instance of Object out of START_ARRAY token

I have two object one is Dashboard and second is Room i have a json which is look like this
{
"hotel_id":"1",
"hotel_room":"200",
"hotel_properties":[{
"id":"1",
"room_type":"Single",
"rack_rate":"2000",
"publish_rate":"1800",
"discount":"10",
"availiable":"40",
"total":"50"
},
{
"id":"2",
"room_type":"Double",
"rack_rate":"4000",
"publish_rate":"3600",
"discount":"10",
"availiable":"45",
"total":"50"
}
]
}
And the Object is
public class DashBoard {
private int hotel_id;
private int hotel_room;
#JsonProperty("hotel_properties")
private Room hotel_properties;
}
There is another Object Room which is look like this
public class Room {
private Long id;
private String room_type;
private String rack_rate;
private String publish_rate;
private String discount;
private String availiable;
private String total;
}
I am Hide all constructor,setter and getter for Stackoverflow but it is in my code
i want parse Json to Object using ObjectMapper from an URL using this code
JsonReader jsonReader = new JsonReader();
ObjectMapper mapper = new ObjectMapper();
try {
JSONObject json = jsonReader.readJsonFromUrl("http://localhost/quinchy/json/dashboard.json");
DashBoard dsh = mapper.readValue(json.toString(), DashBoard.class);
System.out.println(json.toString());
} catch (IOException | JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
but i get this error
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of Object out of START_ARRAY token
please help me out from this

From the JSON String you posted, it looks like there is a list of Room objects. But you have used a single object.
In your DashBoard class, try changing:
private Room hotel_properties;
to:
private List<Room> hotel_properties;

JSON parsing only one branch of whole message java using GsonBuilder and InputStream Android

I just try to integrate with external webservice via JSON from Android. I receive following JSON format:
Data that i'm interested in is in "messages" branch.
To access data i'm using :
builder.setFieldNamingPolicy(FieldNamingPolicy.IDENTITY);
Gson gson = builder.create();
ClassToStore response = gson.fromJson(reader, ClassToStore.class);
where reader is a input stream from:
am = getInstrumentation().getContext().getAssets();
am.open("data.json");
Message structure looks like:
ClassToStore has all fields with the same names.
I get all objects but all of theme are null's
PLEASE HELP :(
My classToStore:
public static class ClassToStore implements Serializable {
private static final long serialVersionUID = -1463052486583654136L;
public String id ;
public String replied_to_id ;
public String sender_id ;
public String created_at ;
public String getId() {
return id;
}
public String getReplied_to_id() {
return replied_to_id;
}
public String getSender_id() {
return sender_id;
}
public String getCreated_at() {
return created_at;
}
}

You will need an extra class to match the outer object:
public class OuterObject {
List<ClassToStore> messages;
}
And then load it like this:
Gson gson = new Gson();
Type type = new TypeToken<List<OuterObject>>(){}.getType();
List<OuterObject> outerList = gson.fromJson(reader, type);
List<ClassToStore> listOfMessages = outerlist.get(0).messages;