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Deserialize a JSON payload to object base on JSON integer property

I have below classes:
public class Result<T> {
public int code;
public Object meta;
public T data;
}
public class User {
public int id;
public String name;
}
public class Error {
public String field;
public String message;
}
I want to deserialize a JSON payload based on code field. If code >= 10, return Result<ArrayList<Error>>, otherwise return Result<User>
Currently, I map JSON to Result<Object> first, then check the code field. Based on that value I make second map to desired object.
ObjectMapper mapper = new ObjectMapper();
Result<Object> tempResult = mapper.readValue(json, new TypeReference<Result<Object>>() {});
if (tempResult.code < 10) {
Result<User> result = mapper.readValue(json, new TypeReference<Result<User>>() {});
return result;
} else {
Result<ArrayList<Error>> result = mapper.readValue(json, new TypeReference<Result<ArrayList<Error>>>() {});
return result;
}
Is there an elegant way to do this without deserializing it 2 times?

You need to implement custom TypeIdResolver:
class UserTypeIdResolverBase extends TypeIdResolverBase {
#Override
public String idFromValue(Object value) {
throw new IllegalStateException("Not implemented!");
}
#Override
public String idFromValueAndType(Object value, Class<?> suggestedType) {
throw new IllegalStateException("Not implemented!");
}
#Override
public JsonTypeInfo.Id getMechanism() {
return JsonTypeInfo.Id.CUSTOM;
}
#Override
public JavaType typeFromId(DatabindContext context, String id) {
if (Integer.parseInt(id) < 10) {
return context.getTypeFactory().constructType(new TypeReference<Result<User>>() {});
}
return context.getTypeFactory().constructType(new TypeReference<Result<List<Error>>>() {});
}
}
and declare it for a Result class:
#JsonTypeInfo(property = "code", use = JsonTypeInfo.Id.CUSTOM, visible = true)
#JsonTypeIdResolver(UserTypeIdResolverBase.class)
class Result<T>

Cannot deserialize instance of `org.json.JSONObject`

I have a basic SpringBoot 2.1.5.RELEASE app. Using Spring Initializer, JPA, embedded Tomcat, Thymeleaf template engine, and package as an executable JAR file with some RestControllers.
In 1 of the controller this is the body I send:
{
"depositHotel": "xxx",
"destinationHotel": "aaa",
"depositHotelAmount": "0.2",
"destinationHotelAmount": "4",
"destinationAddress": [{
"address": "asdf",
"tag": ""
}],
"refundAddress": [{
"address": "pio",
"tag": ""
}]
}
so I create this class to use it as a RequestBody:
public class HotelswitchHotelOrderRequestBody {
public static class Builder {
private String depositHotel;
private String destinationHotel;
private Float depositHotelAmount;
private Float destinationHotelAmount;
private JSONObject destinationAddress;
private JSONObject refundAddress;
public Builder(String depositHotel, String destinationHotel) {
this.depositHotel = depositHotel;
this.destinationHotel = destinationHotel;
}
public Builder withDepositHotelAmount (Float depositHotelAmount) {
this.depositHotelAmount = depositHotelAmount;
return this;
}
public Builder withDestinationHotelAmount (Float destinationHotelAmount) {
this.destinationHotelAmount = destinationHotelAmount;
return this;
}
public Builder toDestinationAddress (JSONObject destinationAddress) {
this.destinationAddress = destinationAddress;
return this;
}
public Builder toRefundAddress (JSONObject refundAddress) {
this.refundAddress = refundAddress;
return this;
}
public HotelswitchHotelOrderRequestBody build(){
HotelswitchHotelOrderRequestBody order = new HotelswitchHotelOrderRequestBody();
order.depositHotel = this.depositHotel;
order.depositHotelAmount = this.depositHotelAmount;
order.destinationAddress = this.destinationAddress;
order.destinationHotel = this.destinationHotel;
order.destinationHotelAmount = this.destinationHotelAmount;
order.refundAddress = this.refundAddress;
return order;
}
}
private String depositHotel;
private String destinationHotel;
private Float depositHotelAmount;
private Float destinationHotelAmount;
private JSONObject destinationAddress;
private JSONObject refundAddress;
private HotelswitchHotelOrderRequestBody () {
//Constructor is now private.
}
public String getDepositHotel() {
return depositHotel;
}
public void setDepositHotel(String depositHotel) {
this.depositHotel = depositHotel;
}
public String getDestinationHotel() {
return destinationHotel;
}
public void setDestinationHotel(String destinationHotel) {
this.destinationHotel = destinationHotel;
}
public Float getDepositHotelAmount() {
return depositHotelAmount;
}
public void setDepositHotelAmount(Float depositHotelAmount) {
this.depositHotelAmount = depositHotelAmount;
}
public Float getDestinationHotelAmount() {
return destinationHotelAmount;
}
public void setDestinationHotelAmount(Float destinationHotelAmount) {
this.destinationHotelAmount = destinationHotelAmount;
}
public JSONObject getDestinationAddress() {
return destinationAddress;
}
public void setDestinationAddress(JSONObject destinationAddress) {
this.destinationAddress = destinationAddress;
}
public JSONObject getRefundAddress() {
return refundAddress;
}
public void setRefundAddress(JSONObject refundAddress) {
this.refundAddress = refundAddress;
}
}
But I have this error when receiving the object:
JSON parse error: out of START_ARRAY token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `org.json.JSONObject` out of START_ARRAY token

JSONObject's representation in actual JSON is a hash i.e. {...}. In your json data you're providing an array of hashes [{...}] which is not the same. Judging from your domain I don't think it has to be multiple values, so you can just omit [] in your payload and if it does then the fields in your Java class can be defined as JSONArray.
However, I think you should go with defining an Address class and either using
private Address destinationAddress;
private Address refundAddress;
or if it indeed does have to be an object array
private List<Address> destinationAddresses;
private List<Address> refundAddresses;

I had a similar usecase , where I could not define the json to a POJO. Using com.fasterxml.jackson.databind.JsonNode instead of the JSONObject worked.

Mapping JSON into POJO using Gson

I have the following JSON to represent the server response for a salt request:
{
"USER":
{
"E_MAIL":"email",
"SALT":"salt"
},
"CODE":"010"
}
And i tried to map it with the following POJO:
public class SaltPOJO {
private String code = null;
private User user = null;
#Override
public String toString() {
return this.user.toString();
}
public String getCode() {
return code;
}
public void setCode(String code) {
this.code = code;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
public class User {
private String e_mail = null;
private String salt = null;
#Override
public String toString() {
return this.e_mail + ": " + this.salt;
}
public String getE_mail() {
return e_mail;
}
public void setE_mail(String e_mail) {
this.e_mail = e_mail;
}
public String getSalt() {
return salt;
}
public void setSalt(String salt) {
this.salt = salt;
}
}
}
Now everytime i do this:
Gson gson = new Gson();
SaltPOJO saltPojo = gson.fromJson(json.toString(), SaltPOJO.class);
Log.v("Bla", saltPojo.toString());
The saltPojo.toString() is null. How can i map my JSON into POJO using Gson?
Is the order of my variables important for the Gson mapping?

Is the order of my variables important for the Gson mapping?
No, that's not the case.
How can i map my JSON into POJO using Gson?
It's Case Sensitive and the keys in JSON string should be same as variable names used in POJO class.
You can use #SerializedName annotation to use any variable name as your like.
Sample code:
class SaltPOJO {
#SerializedName("CODE")
private String code = null;
#SerializedName("USER")
private User user = null;
...
class User {
#SerializedName("E_MAIL")
private String e_mail = null;
#SerializedName("SALT")
private String salt = null;

You don't have proper mapping between your getter and setter. If you change your json to something like below, it would work:
{
"user":
{
"email":"email",
"salt":"salt"
},
"code":"010"
}
If you are getting json form third party then unfortunately, you would have to change your pojo or you could use adapter.

Parsing dynamically generated JSON object names with Jackson

I'm attempting to deserialize some MediaWiki context from JSON using Jackson into POJOs. However, the problem is that one of the JSON object names is the integer ID value of the article, so using an annotation like #JsonProperty can't be used because the value is never constant.
Here's some sample JSON to describe what I mean:
http://en.wikipedia.org/w/api.php?action=query&titles=Albert%20Einstein&prop=info&format=json&indexpageids
{
"query": {
"pageids": [
"736"
],
"pages": {
"736": {
"pageid": 736,
"ns": 0,
"title": "Albert Einstein",
"contentmodel": "wikitext",
"pagelanguage": "en",
"touched": "2014-01-05T03:14:23Z",
"lastrevid": 588780054,
"counter": "",
"length": 106159
}
}
}
}
(MediaWiki recommends adding the &indexpageids parameter to assist with parsing, however I can't see how it would be useful to me.)
I tried using the #JsonAnyGetter and #JsonAnySetter annotations as well but they don't appear to help, throwing the same exception com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "736" (class WikipediaPages), not marked as ignorable (one known property: "wikipediaPage"]).
Thanks for any and all assistance.
Edit: Here's what the relevant classes look like at the moment:
public class WikipediaPages {
private Map<String, WikipediaPage> wikipediaPageMap = new HashMap<String, WikipediaPage>();
public Map<String, WikipediaPage> getWikipediaPageMap() {
return wikipediaPageMap;
}
public void setWikipediaPageMap(Map<String, WikipediaPage> wikipediaPageMap) {
this.wikipediaPageMap = wikipediaPageMap;
}
}
I use a Jackson Mixin to apply annotations:
public interface WikipediaPagesMixIn {
#JsonAnyGetter
Map<String, WikipediaPage> getWikipediaPageMap();
#JsonAnySetter
void setWikipediaPageMap(Map<String, WikipediaPage> wikipediaPageMap);
}
Edit 2: More code, as requested:
public class JacksonBuilder {
private static ObjectMapper objectMapper;
public static ObjectMapper getObjectMapper() {
if(objectMapper == null) {
objectMapper = new ObjectMapper();
objectMapper.registerModule(new WikipediaModule());
}
return objectMapper;
}
}
public class WikipediaModule extends SimpleModule {
public WikipediaModule() {
super("WikipediaModule", new Version(1, 0, 0, null, "net.ryanmorrison", "sentience"));
}
#Override
public void setupModule(SetupContext setupContext) {
setupContext.setMixInAnnotations(WikipediaPage.class, WikipediaPageMixIn.class);
setupContext.setMixInAnnotations(WikipediaPages.class, WikipediaPagesMixIn.class);
setupContext.setMixInAnnotations(WikipediaQuery.class, WikipediaQueryMixIn.class);
setupContext.setMixInAnnotations(WikipediaResult.class, WikipediaResultMixIn.class);
}
}
public class WikipediaResult {
private WikipediaQuery wikipediaQuery;
public WikipediaQuery getWikipediaQuery() {
return wikipediaQuery;
}
public void setWikipediaQuery(WikipediaQuery wikipediaQuery) {
this.wikipediaQuery = wikipediaQuery;
}
}
public interface WikipediaResultMixIn {
#JsonProperty("query")
WikipediaQuery getWikipediaQuery();
}

To answer the root cause of your exception, the #JsonAnySetter javadoc states
Marker annotation that can be used to define a non-static,
two-argument method (first argument name of property, second value to
set), [...]
As such, using a mixin like this
#JsonAnySetter
void setWikipediaPageMap(Map<String, WikipediaPage> wikipediaPageMap);
doesn't register it and therefore the property isn't found.
Honestly, don't use mixins if you control the data classes. You can directly map the fields as I've shown below.
I don't know how you are using your mixin, but the following works for me
String json = "{ \"query\": { \"pageids\": [ \"736\" ], \"pages\": { \"736\": { \"pageid\": 736, \"ns\": 0, \"title\": \"Albert Einstein\", \"contentmodel\": \"wikitext\", \"pagelanguage\": \"en\", \"touched\": \"2014-01-05T03:14:23Z\", \"lastrevid\": 588780054, \"counter\": \"\", \"length\": 106159 } } } }";
ObjectMapper mapper = new ObjectMapper();
JsonNode node =mapper.readTree(json);
node = node.get("query").get("pages");
Map<String, Page> pages = mapper.readValue(node.traverse(), new TypeReference<Map<String, Page>>() {
});
System.out.println(pages);
prints
{736=Page [pageid=736, ns=0, title=Albert Einstein, contentmodel=wikitext, pagelanguage=en, touched=2014-01-05T03:14:23Z, lastrevid=588780054, counter=, length=106159]}
Where Page is
class Page {
private int pageid;
private int ns;
private String title;
private String contentmodel;
private String pagelanguage;
private String touched; // this could be a Date, with the appropriate format configuration
private int lastrevid;
private String counter;
private int length;
#Override
public String toString() {
return "Page [pageid=" + pageid + ", ns=" + ns + ", title=" + title
+ ", contentmodel=" + contentmodel + ", pagelanguage="
+ pagelanguage + ", touched=" + touched + ", lastrevid="
+ lastrevid + ", counter=" + counter + ", length=" + length
+ "]";
}
public int getPageid() {
return pageid;
}
public void setPageid(int pageid) {
this.pageid = pageid;
}
public int getNs() {
return ns;
}
public void setNs(int ns) {
this.ns = ns;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContentmodel() {
return contentmodel;
}
public void setContentmodel(String contentmodel) {
this.contentmodel = contentmodel;
}
public String getPagelanguage() {
return pagelanguage;
}
public void setPagelanguage(String pagelanguage) {
this.pagelanguage = pagelanguage;
}
public String getTouched() {
return touched;
}
public void setTouched(String touched) {
this.touched = touched;
}
public int getLastrevid() {
return lastrevid;
}
public void setLastrevid(int lastrevid) {
this.lastrevid = lastrevid;
}
public String getCounter() {
return counter;
}
public void setCounter(String counter) {
this.counter = counter;
}
public int getLength() {
return length;
}
public void setLength(int length) {
this.length = length;
}
}
All that is left is to put the Map<String, Page> as a field in some wrapper class for the query and pages JSON elements.

Json to Object using Gson

I have a class DocumentBO which has the following attributes -
public class DocumentBO implements IStorageBO {
private String aId;
private String studyId;
private Map<AlgorithmsEnum, JobIOStatus> status;
private String text;
private Collection<Sentence> sentences;
public String getaId() {
return aId;
}
public void setaId(String aId) {
this.aId = aId;
}
public String getStudyId() {
return studyId;
}
public void setStudyId(String studyId) {
this.studyId = studyId;
}
public Map<AlgorithmsEnum, JobIOStatus> getStatus() {
return status;
}
public void setStatus(Map<AlgorithmsEnum, JobIOStatus> status) {
this.status = status;
}
public String getText() {
return text;
}
public void setText(String text) {
this.text = text;
}
public Collection<Sentence> getSentences() {
return sentences;
}
public void setSentences(Collection<Sentence> sentences) {
this.sentences = sentences;
}
}
The AlgorithmsEnum is as follows -
public enum AlgorithmsEnum {
SENTIMENT("sentiment"),
INTENTION("intention"),
TOPIC("topic"),
NER("ner"),
UIMA("uima");
private final String value;
private AlgorithmsEnum(String value) {
this.value = value;
}
public String value() {
return value;
}
#Override
public String toString() {
return value;
}
public static AlgorithmsEnum fromValue(String value) {
if (value != null) {
for (AlgorithmsEnum aEnum : AlgorithmsEnum.values()) {
if (aEnum.value().equals(value)) {
return aEnum;
}
}
}
return null;
}
}
The JobIOStatus is also similar.
I am successfully able to create a JSON string of Collection using GSON using the following TypeToken
Type type = new TypeToken<Collection<DocumentBO>>() {}.getType();
But, when I try to recreate the Collection object using the JSON string returned by Gson and the same TypeToken, the key of the status hashmap is always returned as NULL whereas the value is successfully created. What do you think can be the issue?

The problem is that you have overridden toString() in your enum.
If you look at the JSON being produced, the keys to your Map<AlgorithmsEnum, JobIOStatus> are the lowercase names you're creating. That won't work. Gson has no idea how to recreate the enum from those when you attempt to deserialize the JSON.
If you remove your toString() method it will work just fine.
Alternatively you can use the .enableComplexMapKeySerialization() method in GsonBuilder when serializing which will ignore your toString() method and produce JSON using the default representations of your enum values which is what is required.

There are "well" known :) issues of Gson to serialize Map when the key is derived from object and its not a "native" data type.
Please use this
GsonBuilder builder = new GsonBuilder();
Gson gson = builder.enableComplexMapKeySerialization().create();
Collection<DocumentBO> obj = gson.fromJson(str, type);