Develop Reference

Pass a generic type to Json.encodetostring()

I'm trying to do something from a guide I found online, which is passing a generic type variable to the Json function encodeToString(), I do not want to use a reified type, but it does not work for me...
Here is my sample code:
fun <G> encodetojson(toConvert: G){
converted = Json.encodeToString(toConvert)
return converted
}
From the above code I get a type mismatch error.
How I might fix this?

Is there any way to directly handle json in android/java without convert [duplicate]

I was wondering if somewhere out there exists a java library able to query a JSONObject. In more depth I'm looking for something like:
String json = "{ data: { data2 : { value : 'hello'}}}";
...
// Somehow we managed to convert json to jsonObject
...
String result = jsonObject.getAsString("data.data2.value");
System.out.println(result);
I expect to get "hello" as output.
So far, the fastest way I have found is using Gson:
jsonObject.getAsJsonObject("data").getAsJsonObject().get("data2").getAsJsonObject("value").getAsString();
It's not actually easy to write and read. Is there something faster?

I've just unexpectedly found very interesting project: JSON Path
JsonPath is to JSON what XPATH is to XML, a simple way to extract parts of a given document.
With this library you can do what you are requesting even easier, then my previous suggestion:
String hello = JsonPath.read(json, "$.data.data2.value");
System.out.println(hello); //prints hello
Hope this might be helpful either.

While not exactly the same, Jackson has Tree Model representation similar to Gson:
JsonNode root = objectMapper.readTree(jsonInput);
return root.get("data").get("data2").get("value").asText();
so you need to traverse it step by step.
EDIT (August 2015)
There actually is now (since Jackson 2.3) support for JSON Pointer expressions with Jackson. So you could alternatively use:
return root.at("/data/data2/value").asText();

First of all, I would recommend consider JSON object binding.
But in case if you get arbitrary JSON objects and you would like process them in the way you described, I would suggest combine Jackson JSON processor along with Apache's Commons Beanutils.
The idea is the following: Jackson by default process all JSON's as java.util.Map instances, meanwhile Commons Beanutils simplifies property access for objects, including arrays and Map supports.
So you may use it something like this:
//actually it is a Map instance with maps-fields within
Object jsonObj = objectMapper.readValue(json, Object.class);
Object hello = PropertyUtils.getProperty(jsonObj, "data.data2.value")
System.out.println(hello); //prints hello

You can use org.json
String json = "{ data: { data2 : { value : 'hello'}}}";
org.json.JSONObject obj = new org.json.JSONObject(json);
System.out.println(obj.query("/data/data2/value"));

I think no way.
Consider a java class
class Student {
Subject subject = new Subject();
}
class Subject {
String name;
}
Here if we want to access subject name then
Student stud = new Student();
stud.subject.name;
We cant access name directly, if so then we will not get correct subject name. Like here:
jsonObject.getAsJsonObject("data")
.getAsJsonObject()
.get("data2")
.getAsJsonObject("value")
.getAsString();
If you want to use same like java object then use
ClassName classObject = new Gson().fromJson(JsonString, ClassName.class);
ClassName must have all fields to match jsonstring. If you have a jsonobject inside a jsonobject then you have to create separate class like I'm doing in Student and Subject class.

Using Java JSON API 1.1.x (javax.json) one can make use of new JavaPointer interface. Instance implementing this interface can be considered to some extend as kind of XPath expression analog (see RFC-6901 for details). So in your case you could write this:
import javax.json.*;
//...
var jp = Json.createPointer("/data/data2/value");
System.out.println(jp.getValue(jsonObject));
In 1.1.4 version of JSON there's also nice addition to JsonStructure interface (which is implemented by JsonObject and JsonArray), namely getValue(String jsonPointer). So it all comes down to this simple one-liner:
System.out.println(jsonObject.getValue("/data/data2/value"));

How to start an android project coders view

I've been searching for the past week on how to develop an android project, read some on android developers page and on other websites like here, but no text was complete.
i have this project - i'm a php developer not a java, but could understand a bit about java lately.
the thing is i want to develop an android app using my website, i did output a json type data from my website, and gonna use them on the android app, i did the async request on android and could read the data form the website but :
first question: how to parse the json data correctly and convert it to array on android, i did that through:
Iterator<String> itr = myObject.keys();
while (itr.hasNext()) {
...
i don't know if that's the correct way, when i try to convert my json object to array, it gives me type mismatch.
second and more importantly:
how can create a "Block" like facebook posts style, or twitter style blocks, you know - blocks of json data, is it a linearlayout ? what do i call it ? and how can i add it to the UI dynamically, cuz these blocks are pulled from the website json data. so they are arrays...of blocks..
i'm kinda confused still, i need a start point.
Thank you!

excellent tutorial for beginners for android development
http://thenewboston.org/list.php?cat=6
and for your first question - how to parse json data correctly,
you can try using gson to convert the json data into POJO
otherwise you'd have to do myObject.opt(key) to make sure it is there

First question: you should use a library to parse JSON, it's simpler that way. Try gson. You should create a class, which holds the parsed object, like:
public class Taxi implements Serializable {
private static final long serialVersionUID = 1L;
#SerializedName("idTaxi")
private Integer idTaxi;
#SerializedName("name")
private String name;
//getter, setters, constructor, etc
}
Then when you get the JSON object, you can parse it:
Gson gson = new Gson();
Reader reader = new InputStreamReader(SOURCE_STREAM);
Taxi[] response = gson.fromJson(reader, Taxi[].class);
Second question: i think a ListView would be good for you. You can read a full tutorial about it here

Rest Client with AndroidAnnotations - "no suitable HttpMessageConverter..."

I want to send POST request to server. I have to pass JSON object as a parameter, and get JSON as a response, but I am getting this error:
org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [com.package.Response] and content type [application/octet-stream]
Code
Sending request:
#RestService
RestClient restClient;
...
String json = "{\"param\":3}";
restClient.getRestTemplate().getMessageConverters().add(new GsonHttpMessageConverter());
Response res = restClient.send(json);
RestClient
#Rest("http://my-url.com")
public interface RestClient
{
#Post("/something/")
Response send(String json);
RestTemplate getRestTemplate();
void setRestTemplate(RestTemplate restTemplate);
}
I'm using these JAR files:
spring-android-rest-template-1.0.0.RC1
spring-android-core-1.0.0.RC1
spring-android-auth-1.0.0.RC1
gson-2.2.2
What I'm doing wrong? When I change send parameter to JSONObject I am getting the same error.
Btw. AA docs are really enigmatic - can I use Gson anyway? Or should I use Jackson? Which file do I need to include then?
Thanks for any help!

You can use RestTemplate with either Gson or Jackson.
Gson is fine and easier to use of you have small json data set. Jackson is more suitable if you have a complex / deep json tree, because Gson creates a lot of temporary objects which leads to stop the world GCs.
The error here says that it cannot find a HttpMessageConverter able to parse application/octet-stream.
If you look at the sources for GsonHttpMessageConverter, you'll notice that it only supports the mimetype application/json.
This means you have two options :
Either return the application/json mimetype from your content, which would seam quite appropriate
Or just change the supported media types on GsonHttpMessageConverter :
String json = "{\"param\":3}";
GsonHttpMessageConverter converter = new GsonHttpMessageConverter();
converter.setSupportedMediaTypes(new MediaType("application", "octet-stream", Charset.forName("UTF-8")));
restClient.getRestTemplate().getMessageConverters().add(converter);
Response res = restClient.send(json);

I just had this problem. After several hours I realised that the class I was passing in to the RestTemplate.postForObject call had Date variables. You need to make sure it only contains simple data types. Hope this helps someone else!

I have to modify it little to work:
final List<MediaType> list = new ArrayList<>();
list.addAll(converter.getSupportedMediaTypes());
list.add(MediaType.APPLICATION_OCTET_STREAM);
converter.setSupportedMediaTypes(list);

Parsing an object with variable type in gson

I have something like the following json string:
{"values" : [
{ "group":"A"
"rating":2
},
{
"group":"B"
"language":"english"
}
]
}
As you can see, "values" is an array, with different type of objects. One type can contain a string and an integer, and the other type contains a string and another string.
How do I deal with this?

Sorry, I didn't notice originally you wrote "gson". I'm not sure you can do it, and here's not me saying it.

Do some thing like the following
List myStrings = new ArrayList();
myStrings = gson.fromJson(json,myStrings.getClass());
Iterator myIterator = myStrings.iterator();
boolean b;
while(myIterator.hasNext()){
Object o =myIterator.next();
b=o instanceof String;
System.out.println("...."+b);
}

My approach would probably be to implement a polymorphic deserialization solution.
Gson does not currently have a simple mechanism for polymorphic deserialization, other than implementing custom deserialization processing. The next release looks like it will provide a built-in solution.
Previous StackOverflow.com Questions And Answers (Some With Examples) On This Topic:
Deserialising a generic with unknown compile time type where a field indicates the type
Parse JSON with no specific structure for a field with GSON
json object serialization/deserialization using google gson
Polymorphism with gson
Specific to the original question, it looks like the "group" element would be used to distinguish between different types.
FWIW, Jackson released a built-in solution to this problem many moons ago.