I have to convert a json into an object using jackson. The class is like:
class Country {
int a;
int b;
}
And the json i am getting:
{"country":{"a":1,"b":1}}
But when i am trying to deserialize this its giving me following error
org.codehaus.jackson.map.JsonMappingException: Unrecognized field "country"
If i remove "country", i am able to get the object.
Is there any way i can tell jackson to just ignore "country" from the json string?
Thanks in advance.
This is the correct behavior of Jackson, the actual json representation of Country object should be without the top level country. If your json absolutely has the top level country attribute, a cleaner approach would be to use a wrapper Country class like this:
class WrapperCountry {
Country country;
}
this way the json representation should correctly deserialize to the WrapperCountry object and you can retrieve country from that.
Related
I'm not sure if this type of problem was already asked. I couldn't find, so asking
I have a POJO
Class A {
int id;
Object data;
//getter and setters
}
I set org.json.JSONObject type json into data
Option 1:
When I set data to object directly, I get an error from ObjectMapper when doing
objectMapper.writeValueAsString(anInstanceOfA);
Error: InvalidDefinitionException: No serializer found for org.json.JSONObject
{ I assume the problem is between fasterxml and org.json }
Option 2:
If I use toString on JSONObject before setting to an instance of A, I see escape character in the output. The output is unacceptable. Can't sacrifice JSON formatting and structure
Is there a way to leave already JSON structured element as-is, with less conversions?
In Java, using Jackson, I want to deserialize JSON that looks something like this:
{
"123_ABC": {
"XYZ": 768,
"123_DATA": {
"123_DEF": "",
"123_ACT": "ZAC",
"123_PAG": {
"123_PAG_A": 1,
"123_PAG_B": 1
}
}
}
}
You all know that identifiers starting with a number are invalid in Java (and every programming language I ever heard of.)
I already know how to use #JsonProperty to translate field names, but handling class names is outside my knowledge.
If I define classes corresponding to the structure of the JSON, but with valid class names, is there a way to use Jackson annotations to map the invalid class id in the JSON to my valid class names?
I think #JsonProperty should be good to deserialize this.
Let's create a wrapper class that will have 123_ABC as a property of class ValidClass.
class Wrapper {
#JsonProperty("123_ABC")
private ValidClass validName;
}
Now, when you serialize, it will create JSON like this (or can be deserialized using that)
{ "123_ABC":{ //PROPERTIES OF ValidClass HERE } }
Similarly, you can have different properties in further inner classes.
In case if you to support 123_ABC only for deserialization and serialize with correct field names, you can do like this
#JsonAlias("123_ABC")
private ValidClass validName;
it will serialize to following.
{"validName": {//properties}}
but deserialization can be done using both
{"validName": {//properties}}
{"123_ABC": {//properties}}
In case, if keys keep changing, I would suggest to deserialize them in Map.
I am having troubles when JSON is being deserialized using Jackson.
The problem is when the JSON is deserialized and whatever JSON property is changed by DEV, I still need to get it deserialized into an object.
Here is the part of variables in the object
#JsonProperty("accountingFiscalYear")
public String accountingFiscalYear;
#JsonProperty("amount")
public Float amount;
#JsonProperty("debitFlag")
public Boolean debitFlag;
and here is the JSON part
"accountingFiscalYear": "2017",
"amount": 1632.0000,
"debitFlag": true,
When it runs it is deserialized without any problems. But if there is any change in the JSON response it fails during the deserialization like:
For example if I change the debitFlag data type from Boolean to Integer
com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of int out of VALUE_TRUE token
I know it is right, but I would like to continue with deserialization and simply ignore types that could not be deserialized and keep them null.
Thanks for hints.
What is the basic purpose of #SerializedName annotation in Android using Gson?
Give me some different examples. I can't understand the main purpose of using it.
Java class example,
public class Person {
#SerializedName("name")
private String personName;
#SerializedName("bd")
private String birthDate;
}
This class has two fields that represent the person name and birth date of a person. These fields are annotated with the #SerializedName annotation. The parameter (value) of this annotation is the name to be used when serialising and deserialising objects. For example, the Java field personName is represented as name in JSON.
JSON Example,
{
"name":"chintan",
"bd":"01-01-1990"
}
There are already few answers here,but I would like to add that if you are using ProGuard to Obfuscate your code & don't use #SerializedName("name") in your model class, then your GSON won't work. Because due to obfuscation, your variable names might have changed from String name to String a resulting into broken GSON parsing as GSON will look for key a into json & it will fail.
By specifying #SerializedName, GSON will not look in json based on variable name & will just use specified #SerializedName.
Of Course you can tell proguard to not obfuscate your model, but if you would like to have model obfuscated, then you must specify #SerializedName
Using #SerializedName you are actually telling the Parser when receiving a callback from the server i.e. of a Json format:
{
"name":"John Doe",
}
that when Serializing or Deserializing an object to instead of searching for a key named: "userName", in the Json response, to search for "name".
#SerializedName("name")
var userName: String,
This is good because you may have a model that you would like it to have its members being called with whatever you like.
You can instruct Proguard to not obfuscate your data classes by specifying #Keep on top of the class. This will neither remove nor obfuscate your class. No need to add #SerializedName to each and every field explicitly if the field name is similar to the Json key being used for it.
Let's say in a real-world scenario, your backend dev is giving you this response for an API request you make
{
"name":"John Doe",
"id":"1478"
}
Now, in the data class you make to handle this, there might be chances you want to specify a different variable name at Android side for the fields "name" and "id" that you are getting from backend.
#SerializedName comes to rescue here.
You just need to specify the actual key value you will be getting from backend in the #SerializedName (which will be used to serialize and deserialize) and then you can use a variable name of your choice that stores that value received from the operation.
For example, for the JSON I mentioned earlier, here is how its data class will look like:
data class User(
#SerializedName("name") val userName: String,
#SerializedName("id") val userId: Int
)
Here name, id is used in #SerializedName because it's the backend key.
But I have used userName, userId to store those values.
Given this JSON response I get from an website :
{
"Items":
[
{ "Name":"Apple", "Price":12.3, "Quantity":30 },
{ "Name":"Grape", "Price":3.21, "Quantity":60 }
],
"Date":"21/11/2010"
}
How could i deserialize this JSON, splitting it in an array called Fruits, containing only name and quantity ? I don't care about date field or other fields like price.
My class should look like:
class Fruit{
String name;
String quantity;
}
And this is the array:
Fruit myfruits[] = new Fruit [this number depends on JSON response I get]
How could I achive this ?
I've tried to give my best explanation, if it is still not clear, feel free to ask.
P.S: btw, the real JSON response has many more fields
You need to ignore the fields you don't wont.
Each serialization frameworks does it in different ways.
In some you can add annotations to you POJO, or set it with the serializer instance
Using Gson:
Gson ignore json field and deserialize
Using Jackson:
Ignoring new fields on JSON objects using Jackson