Develop Reference

How do I convert a LinkedTreeMap to gson JsonObject

For a java data handler, I send properly formatted JSON, but a combination of Spring, Java deciding how to cast what it sees, and frameworks I really shouldn't go changing mangle that JSON so that once I can see it, it's turned into a LinkedTreeMap, and I need to transform it into a JsonObject.
This is not to serialize/de-serialize JSON into java objects, it's "final form" is a gson JsonObject, and it needs to be able to handle literally any valid JSON.
{
"key":"value",
"object": {
"array":[
"value1",
"please work"
]
}
}
is the sample I've been using, once I see it, it's a LinkedTreeMap that .toString() s to
{key=value, object={array=[value1, please work]}}
where you can replace "=" with ":", but that doesn't have the internal quotes for the
new JsonParser().parse(gson.toJson(STRING)).getAsJsonObject()
strategy.
Is there a more direct way to convert LinkedTreeMap to JsonObject, or a library to add the internal quotes to the string, or even a way to turn a sting into a JsonObject that doesn't need the internal quotes?

You'd typically have to serialize the object to JSON, then parse that JSON back into a JsonObject. Fortunately, Gson provides a toJsonTree method that kind of skips the parsing.
LinkedTreeMap<?,?> yourMap = ...;
JsonObject jsonObject = gson.toJsonTree(yourMap).getAsJsonObject();
Note that, if you can, just deserialize the JSON directly to a JsonObject with
gson.fromJson(theJson, JsonObject.class);

Reading from big json data in java

To start off, I'm pretty new in programming. I have to create an Android Weather App for a school project and I'm stuck with this big ass JSON:
JSON Data
Out of this, how would I read the temperature out of every 3 hour interval(example: 9.00-12.00 temperature: 5°C, 12.00-15.00 temperature: 7°C etc.).
So I have an Activity that displays the temperature of the entire day by three hour intervals. Since I have no experience with JSON I have no idea what the certain indexes mean, when does it increment(there are like 8 main: thingies).
DISCLAIMER: I have to use JSON, no GSON or other shortcuts, I have to parse and read certain data from this JSON. I get this JSON from open weather map API so it changes every day.
API

Use volly library for it. You can easily fetch data from json. No async task is needed, if you are using volly library.

First validate the json by going to http://jsonlint.com/. This will help you see the formatted Json string.
Next read up on Json array and Object .
Use AsynTask to get the Json into forecastJsonStr string.
Then you need to convert this forecastJsonStr into JSon object forecastJsonObj
To get weather data in "list" do something similar to
JSONArray weatherArray = forecastJson.getJSONArray("list");
Hope this helps

JSONObject receivedData = new JSONObject("The string that you get as response from the API");
JSONArray weatherList = receivedData.getJSONArray("list");
for(int i=0;i<weatherList.length();i++){
JSONObject data = weatherList.getJSONObjectAt(i);
String date_text - data.getString("dt_txt");
JSONArray weatherData = weatherList.getJSONArray("main");
for(int j=0;j<weatherData.length();j++){
// Here is where you will get all the weather stuff that you need
int temp = weatherData.getInt("temp");
// Similarly other values like temp_min, temp_max
}
}
So basically you need to parse the entire thing. In order to understand the whole structure more clearly use something like http://jsonviewer.stack.hu/ in order to view the JSON in a more clear way so that you know what you need from the JSON data better. Simple copy paste your data into there and click "Format".
JSON is just a name-value pair kind of storage if you see stored like "name":"value". Integer values don't have the "".
Remember all the JSON is stored in { } and a JSON can be nested in a JSON. So in your example if you see, the entire thing is a JSON. Within that you have a "city" key which has a value within { }. So "city" is a JSONObject.
Similarly "coord" is a JSONObject while "cod" is a String and "cnt" is an integer.
There can also be some instances where a name points to an array of JSON objects like "list" over here. JSON Arrays are signified using a [ ]. Enclosed within are JSON objects separated by comma.
Above is a very simple sample to get you started so that you get a jist of what is going on. So play around and try to extract more data from in there.
All the best and Happy Coding :)

A method to get JSON key values as a list

I have a requirement where in I have to get all the key values of a json returned now I am getting the json as a string.
String test = obj.returnJSON();
I need to get the JSON key values as a list is there any predefined method or I have just to write my own logic.
Thanks
KD

Use the JSON in Java library http://json.org/java/ or the google-gson library https://code.google.com/p/google-gson/. Either of these will parse the javascript string into an object, and you can get the keys from there.

Using the Java org.json parser you could do it as
String test = obj.returnJSON();
JSONArray keys = new JSONObject(test).names();
System.out.println(keys.getString(0)); // key1

the google library, GSON, is WAY BETTER and very useful.
I had the same problem and found the answer here
Best regards!

Java object from JSON input file

Hi I have a json input file as follows,
{'Latitude':'20',
'coolness':2.0,
'altitude':39000,
'pilot':{'firstName':'Buzz',
'lastName':'Aldrin'},
'mission':'apollo 11'}
How to create a java object from the json input file.
Thanks

You can use the very simple GSON library, with the Gson#fromJson() method.
Here's an example: Converting JSON to Java

There are more than one APIs that can be used. The simplest one is JSONObject
Just do the following:
JSONObject o = new JSONObject(jsonString);
int alt = o.getInt("altitude");
....
there are getXXX methods for each type. It basically stores the object as a map. This is a slow API.
You may use Google's Gson, which is an elegant and better library -- slightly more work required than JSONObject. If you are really concerned about speed, use Jackson.

org.json.JSONObject constructor not accepting what appears to be a valid JSON string

I have a string in an Android app that I am trying to convert into a JSONObject. The string looks like this (except longer and with actual values instead of the dummy values I entered here):
[[{"1":"a"}],[{"1a":"1a","1b":"1b"},{"2a":"2a","2b":"2b"}]]
I have entered this exact string into two online JSON validators, and both of them confirm it to be valid JSON data. So I would assume that the JSONObject constructor would be able to accept this string and convert it into a JSONObject. But when I try:
json = new JSONObject(result);
Where "result" is a String variable containing the string listed above, I get the following exception:
JSONException: A JSONObject text must begin with '{' at character 1 of [[{"1":"a"}],[{"1a":"1a","1b":"1b"},{"2a":"2a","2b":"2b"}]]
What's going on here? Is the JSONObject's parser broken?

You are trying to create a JSONObject, but what you are actually giving it is a JSONArray. Did you try creating a JSONArray instead?
Alternatively, you could wrap your array in an object so that you can create a JSONObject out of it.

I would suggest using the GSon library instead as it appears to be more full-featured.
In addition, it may be helpful to use this tool to test your data (your data is valid btw):