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Convert String to ArrayList<String> using GSON

I am trying to deserialize a JSON data to a POJO.
The issue is that the list object is coming as a string, and gson gives an IllegalStateExceptioState. How can I parse the string as a list to an ArrayList using gson?
JSON DATA
{
"report_id":1943,
"history_id":3302654,
"project_id":null,
"owner_emails":"[\"abcd#xyz.com\"]",
"message":"Array\n(\n [name] => SOMENAME\n [age] => 36\n [gender] => male\n)\n"
}
POJO:
public class EventData {
private static Gson gson = new Gson();
#SerializedName("report_id")
public String reportID;
#SerializedName("history_id")
public String historyID;
#SerializedName("project_id")
public String projectID;
#SerializedName("owner_emails")
public ArrayList<String> ownerEmails = new ArrayList<String>();
#SerializedName("message")
public String message;
#SerializedName("title")
public String title;
public CrawlerNotifiedEventData(){
this.projectID = "Undefined";
this.reportID = "Undefined";
this.historyID = "Undefined";
this.title = "";
}
public String toJson(boolean base64Encode) throws java.io.UnsupportedEncodingException{
String json = gson.toJson(this, CrawlerNotifiedEventData.class);
if(base64Encode)
return Base64.getEncoder().encodeToString(json.getBytes("UTF8"));
return json;
}
public String toJson() throws java.io.UnsupportedEncodingException{
return this.toJson(false);
}
public static EventData builder(String json){
return gson.fromJson(json, EventData.class);
}
}
Deserialization:
EventData eventData = EventData.builder(json);
While deserializing i get the following error
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was STRING at line 1 column 252 path $.owner_emails

Boxing structured data in a string where it is unnecessary is a very common design issue across different serialization approaches. Fortunately, Gson can deal with fields like owner_emails (but not message of course).
Merely create a type adapter factory than can create a type adapter for a particular type by substituting the original one and doing a bit of more work. The adapter is supposed to read the payload as string and delegate the string deserialization to the type adapter it substitutes.
public final class JsonStringBoxTypeAdapterFactory
implements TypeAdapterFactory {
private JsonStringBoxTypeAdapterFactory() {
}
#Override
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> typeToken) {
final TypeAdapter<T> adapter = gson.getAdapter(typeToken);
return new TypeAdapter<T>() {
#Override
public void write(final JsonWriter out, final T value) {
throw new UnsupportedOperationException(); // TODO
}
#Override
public T read(final JsonReader in)
throws IOException {
return adapter.fromJson(in.nextString());
}
};
}
}
#AllArgsConstructor
#ToString
#EqualsAndHashCode
final class EventData {
#SerializedName("owner_emails")
#JsonAdapter(JsonStringBoxTypeAdapterFactory.class)
List<String> ownerEmails;
}
The unit test below will be green:
final EventData eventData = gson.fromJson(json, EventData.class);
Assertions.assertEquals(new EventData(ImmutableList.of("abcd#xyz.com")), eventData);
That's it.

"owner_emails" is curently a string as follows
"owner_emails":"[\"abcd#xyz.com\"]"
It should be
"owner_emails": ["abcd#xyz.com"]
to be considered as array. You can manually remove the quotes and parse it.
Or you can parse it using JsonElement in Gson

You can use ObjectMapper from jackson library for this conversion.
Sample code of conversion::
public <T> T mapResource(Object resource, Class<T> clazz) {
try {
return objectMapper.readValue(objectMapper.writeValueAsString(resource), clazz);
} catch (IOException ex) {
throw new Exception();
}
}
Modify the model for a list like::
public class Reportdata{
private List<String> owner_emails = new ArrayList();
#JsonDeserialize(contentAs = CustomClass.class)
private List<CustomClass> customClassList = new ArrayList();
....// setter and getter
}
In addition to this, while creating the ObjectMapper object you can pass or register the module/ your custom module for deserialization in object like below.
objectMapper.setDefaultPropertyInclusion(Include.NON_EMPTY);
objectMapper.disable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING);
objectMapper.registerModule(new JavaTimeModule());

How to read JSON String attribute into custom class object using Gson?

When reading a JSON :
{"field":"value"}
into a String field :
public class Test {
private String field;
}
using Gson.fromJson it works as intended and the member String field gets the value "value".
My question is, is there a way to read the same JSON into a custom class so that the custom class object can be constructed with the String value? e.g.
public class Test {
private MyField<String> field;
}
public class MyField<T> {
private T value;
public MyField(T v) {
value = v;
}
}
The reason being the String class is final and cannot be extended, yet I don't want the JSON to be changed into this :
{"field":{"value":"value"}}
If there is a way to extend the String class, it is the best. Otherwise, will need a way for Gson to read string into a custom class that can be constructed by string. Something to do with writing a custom TypeAdapter?

You can use custom JsonDeserializer, JsonSerializer. Here is simple demo version:
static class MyFieldAsValueTypeAdapter<T> implements
JsonDeserializer<MyField<T>>, JsonSerializer<MyField<T>> {
private Gson gson = new Gson();
#Override
public MyField<T> deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context)
throws JsonParseException {
JsonObject obj = new JsonObject();
obj.add("value", json);
return gson.fromJson(obj, typeOfT);
}
#Override
public JsonElement serialize(MyField<T> src, Type typeOfSrc,
JsonSerializationContext context) {
return context.serialize(src.getValue());
}
}
public static void main(String[] args) {
GsonBuilder b = new GsonBuilder();
b.registerTypeAdapter(MyField.class , new MyFieldAsValueTypeAdapter());
Gson gson = b.create();
String json = "{\"field\":\"value1\"}";
Test test = gson.fromJson(json, Test.class);
}
Be careful with internal Gson gson = new Gson(). If you have some other setup, you will need to register it on internal version or pass default MyField deserializer/serializer to your custom implementation.

Apache Camel - GSON JsonSerializer use on routes

I have a endpoint with Camel that returns properties as JSON but are not with the proper order. The return class has a superclass that returns some control data which is necessarily to be present in every return.
public class Respuesta implements Serializable {
#SerializedName("subject")
#Expose
private String subject;
#SerializedName("action")
#Expose
private String action;
#SerializedName("status")
#Expose
private Integer status;
#SerializedName("description")
#Expose
private String description;
...getter/setter
And the final return class inherits that piece.
public class FacturadoresListarResponse extends Respuesta implements Serializable {
#SerializedName("lst")
#Expose
private List<Facturador> listaProveedores;
public FacturadoresListarResponse(List<Facturador> listaProveedores) {
super();
this.listaProveedores = listaProveedores;
}
public FacturadoresListarResponse() {
}
public void setRespuesta(Respuesta rsp) {
super.setAction(rsp.getAction());
super.setDescription(rsp.getDescription());
super.setStatus(rsp.getStatus());
super.setSubject(rsp.getSubject());
}
getter/setter...
}
So, the Gson's Marshaller takes first the inherited class property (lst), and then the parent class properties (subject, status, etc.), giving this kind of result on the wire.
{
"lst": [
{
"rut": "XXXX-X",
"rzsoc": "XXXXXXx",
"res": 1,
"ema": "a#a.cl"
}
],
"subject": "facturadores",
"action": "listar",
"status": 0,
"description": "OK"
}
I wrote a GSON custom JsonSerializer that builds data in order, but I can't use in a Camel DSL syntax. I tried, but without results:
.marshal().json(JsonLibrary.Gson,FacturadoresListarRspSerializer.class, true)
.convertBodyTo(String.class, "UTF-8")
Is there supported by Camel to use these kind of serializers to achieve proper order without migrating to Jackson?
Note: The code of the serializer (FacturadoresListarRspSerializer.class).
public class FacturadoresListarRspSerializer implements JsonSerializer<FacturadoresListarResponse> {
#Override
public JsonElement serialize(FacturadoresListarResponse src, Type typeOfSrc, JsonSerializationContext context) {
final JsonObject jsonObject = new JsonObject();
jsonObject.addProperty("subject", src.getSubject());
jsonObject.addProperty("action", src.getAction());
jsonObject.addProperty("status", src.getStatus());
jsonObject.addProperty("description", src.getDescription());
final JsonArray jsarrFacturadores = new JsonArray();
for (final Facturador fact : src.getListaProveedores()) {
JsonObject jsobFacturadores = new JsonObject();
jsobFacturadores.addProperty("rut", fact.getRutCompleto());
jsobFacturadores.addProperty("rzsoc", fact.getRazonSocial());
jsobFacturadores.addProperty("res", fact.getResolucion());
jsobFacturadores.addProperty("ema", fact.getCorreoEnvio());
jsarrFacturadores.add(jsobFacturadores);
}
jsonObject.add("lst", jsarrFacturadores);
return jsonObject;
}
}

Create a new GSON instance:
Gson gson = new GsonBuilder().registerTypeAdapter(FacturadoresListarResponse.class,
new FacturadoresListarRspSerializer()).create();
Create a new GsonDataFormat by specifying the previously created Gson instance:
GsonDataFormat gsonDataFormat = new GsonDataFormat(gson, FacturadoresListarResponse.class);
Specify the previous data format in your RouteBuilder's marshal(DataFormat dataFormat) method:
.marshal(gsonDataFormat)

Gson parse to POJO with custom key

I have json data like this:
meds:
[
{
MedsID: 8063,
updated_at: "2015-11-04T06:59:55",
treatment_date: "2015-11-04T00:00:00",
name: "name"
}
],
scores:
[
{
ScoreID: 75820,
updated_at: "2015-11-04T06:59:55"
dialysis_flow: 233,
}
],
dias:
[
{
DiasID: 75820,
updated_at: "2015-11-04T06:59:55"
name: "K",
}
]
And here is my Entities:
public class BaseData{
public long id;
}
public class Med extends BaseData{
public String name;
public String updated_at;
public String treatment_date;
}
public class Score extends BaseData{
public String updated_at;
public int dialysis_flow;
}
public class Dias extends BaseData{
public String name;
public String updated_at;
public String treatment_date;
}
Because all entities are mapped from database with the id key (as I use orm db, it's loaded by property name ). So I need to parse all other keys MedsID, DiasID, ScoreID into id when mapping by gson. Is there any way to achieve that?
Update:
I use registerTypeHierarchyAdapter instead of registerTypeAdapter and it can work. But this way is extremely slow as my json data is very large.
public class DataDeserializer implements JsonDeserializer<BaseData> {
#Override
public BaseData deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
JsonObject ja = json.getAsJsonObject();
Gson gson = new Gson();
final String[] mapIds = {"ScoreID", "MedsID", "DiasID"};
BaseData data = gson.fromJson(ja, typeOfT);
for (String idKey:mapIds){
if(ja.has(idKey)){
data.id = ja.get(idKey).getAsLong();
break;
}
}
return data;
}
}
Gson gson = new GsonBuilder().registerTypeHierarchyAdapter( BaseData.class, new DataDeserializer() ).create();
Does anyone know other way to achieve that?

The only way to achieve this is writing a custom de-serializer. Please see below example:
public class CustomDeserializer implements JsonDeserializer<Dias>{
public Dias deserialize( JsonElement json, Type typeOfT, JsonDeserializationContext context ) throws JsonParseException{
JsonObject ja = json.getAsJsonObject();
Dias dias = new Gson().fromJson( ja, Dias.class );
dias.id = ja.get( "DiasID" ).getAsLong();
return dias;
}
}
Register it;
String dias = "{'DiasID':75820,'updated_at':'2015-11-04T06:59:55','name':'K'}";
Gson gson = new GsonBuilder().registerTypeAdapter( Dias.class, new CustomDeserializer() ).create();
Dias dias2 = gson.fromJson( dias, Dias.class );
System.out.println( dias2.id );
Output:
75820
This is just an example, you can extend it by writing a deserializer for your own base class.

Gson - Deserialize objects by specifying class, not parametrization

I have the following classes:
public class Top {
private String key;
...
}
public class A extends Top {
private String aValue;
...
}
public class Complex {
private String field;
private List<Top> objects;
}
I want to deserialize a json String into a "Complex" class and specify that "objects" elements are of type "A".
I have tried 2 methods:
Gson gson = new GsonBuilder()
.setPrettyPrinting()
.registerTypeAdapter(A.class, new InstanceCreator<A>() {
#Override
public A createInstance(Type arg0) {
return new A();
}
}) //method 1
.registerTypeHierarchyAdapter(A.class, new My_A_Adapter()) //method 2
.create();
Complex complexObject = gson.fromJson(json, Complex.class);
A = (A) complexObject.getObjects().get(0); // This throws ClassCastException
But the type of complexObject.getObjects().get(0) is "Top" so i cannot cast it to "A".
I do not want to parameterize the Complex class, (for ex. Complex) because i want to add more collections of generic objects in time...
What solution do I have ?