Develop Reference

How to get hits data from elasticsearch in Java

I have elasticsearch response stored as a String value in java,How to process only hits data

For example, you want to retrieve all data as Car type. Your query response is store in searchResponse variable, get all hits and serialize them to the objects.
Look at the example below:
Gson gson = new Gson();
var flowers = new ArrayList<Flower>();
Arrays.stream(searchResponse.getHits().getHits()).forEach(hit ->
cars.add(gson.fromJson(hit.getSourceAsString(), Car.class)));
Of course, I am using gson to serialize the JSON to the object.

The best way to access it from Java is to use the official Java REST API from Elastic. The API will let you work with Java objects instead of processing the data yourself.

You first need to convert the json string to a json/map object, either using gson, Jackson, or other method.
Then, once you have a Map, the hits are under: hits.hits key, as an array of maps, each map in the array represent a hit, with its metadata. The original doc is under the key _source in each hit.
I also highly recommend reading elasticsearch docs, which are good source.

Converting JSON Object(s) from file using Java

I have a JSON file with no clue on how data will be in it nor the structure of data.
The only thing known is that it will have either an array of JSON objects or a single JSON object.
I need to get each object from the file and store it as a separate item. In case of array of objects in the file, I should get an array of JSON strings which I can store in DB.
Basically, I need to read this file and separate out each JSON object from it and store it in DB as a string.
One of the ways to do it was to use JACKSON ObjectMapper and assign these items to a Hashmap as key value pairs, but I am not sure though how it can be done If there are list of JSON Objects in the file.
Sample JSON File:
[
{
"name":"Bob",
"type":"Email",
"from":"a#a.com",
"to":"b#B.com",
"attachments":[...],
.
.
.
}
]

Do you know the Object structure that the JSON has(let it be Array or a single one) ? If Yes,
First load the json string form the file into an in memory string.
check the string for Array existence, by searching for '[',']' in the outer structure of multiple occurrences of '{' or '}'
once you know whether you have an array or a single object, you can pass it as object reference to either Jackson or GSON parsers
create in memory Array of JsonObject.class say List. It is actually better to enclose this List inside another class. say myJsonObjects and have a List inside it.
Let us see GSON parsers (by google), though Jackson can also be used in the similar implementation
Gson gson = new Gson();
if(isArray){
myJsonObjects jsonArray = gson.fromJson(jsonStringFromFile,myJsonObjects );
}
else{
gson.fromJson(jsonStringFromFile,JsonObject);
}
http://google-gson.googlecode.com/svn-history/trunk/gson/docs/javadocs/com/google/gson/Gson.html

Jackson is my favorite JSON-to-POJO library. It doesn't really matter where you're loading the JSON from (a URL or from the filesystem), there are handlers for several input sources.
Here's an example:
Map<String,Object> userData = mapper.readValue(new File("user.json"), Map.class);
As far as having an unknown number of JSON structures that you're about to parse, the first thing that comes to mind is to have a mapper for each type you're expecting. You could then wrap the parsing code in try/catch blocks so that if the first fails with whatever exception Jackson gives you when encountering an unexpected format, you can then try the next format and so on.
If you're just trying to generically parse JSON that you don't know the structure of beforehand, you can try something like this:
mapper.readValue(jsonString, new TypeReference<List<EntryType>>() {});
The documentation for Jackson is pretty good-- giving it a solid read-through should definitely help. Here's a good five minute tutorial: http://wiki.fasterxml.com/JacksonInFiveMinutes

I prefer use Gson:
Gson gson;
Map<String, Object>parameters=gson.fromJson(myString);
the rest is iterate the map, i hope help you

Parsing JSON into a string array or xml

I am trying to connect to a server which than connect to Google Places API and returns me my required data, the data that is being returned is in this format Here
Now in my Android Application i have this as a string or string[], issue is how can i now parse it as an XML or convert it to a native type like a List or something so i can than use it?
If you look at the returned string the actually array results starts after the two elemenets html_attributions & next_page_token so how can i seperate these and parse. Please help.

I would recommend you using the Gson library from Google, it can easily convert JSON -> Object . Here is a nice tutorial for you : tutorial.
This library is used by famous library Retrofit which is made for these calls and it will download the data and convert it to object using Gson : retrofit

There are a variety of ways to perform Json parsing in android.
If you only want to take the json and convert it to a java objects, then you can use gson. When serializing the object, gson will ignore any key in the json that doesn't match the java object that you are going to use for serialization. Therfore, just create your java object with the results instance variable,
https://code.google.com/p/google-gson/
You can use the built in JsonReader class to obtain the "results" and place that into a json array, if you want to single that out.
It is also good to become familiar with retrofit. This library provides a little more functionality than your solution needs however. This library abstracts the whole http request, response, json parsing and gson serializtion for you. So simply, you call a method on the object and get back the json in already serialized pojo.
http://square.github.io/retrofit/

If your returned data is in json format, create one JsonObject, Parse it as Json instead of xml, you can retrieve the value and create String[]. Take help from this tutorial
Of-course you can use Gson library to serialize and de-serialize jsonObject to pojoObject.

Ideally you should use a cool convenient library like Google GSON as mentioned by others for JSON parsing, but I'll explain how to use your json string with the old simple org.json library anyway. If your json string returned from server is in a string s, do:
JSONObject places=new JSONObject(s);
JSONArray results=places.getJSONArray("results");
for(int i=0;i<results.length();i++){
System.out.println(results.getJSONObject(i).getString("place_id"))
System.out.println(results.getJSONObject(i).getString("scope"));
}

Parse JSON String into raw Java types using Jackson?

I would like to parse some JSON string the represents either an array or a map in the simplest possible way. I have the whole JSON string, no streaming is needed.
What I would like to do is something as similar as possible to this:
Object obj = parseJSON(theString);
Where obj would then hold an instance of either a Map or a List (I cannot know in advance which). The JSON object can be arbitrarily nested with maps and arrays but all types will be representable as basic Java types: String, Integer, Double, Boolean plus Map and ArrayList, nothing else.
All the simple examples I have found so far require me to know what the type is and which types I want, but I want to let all this do the JSON parser since I simply will not know in advance what I get.
If Jackson is not the best library to do this, what else could I use?

All you need to do is this:
ObjectMapper mapper = new ObjectMapper();
Map<String,Object> map = mapper.readValue(theString, Map.class);
I'm pretty sure this returns a LinkedHashMap, if you care.
And in my opinion, you won't find a better serializer/deserializer for Java <-> JSON than Jackson. But there are many others like GSON.

Silly question, simple answer:
import com.fasterxml.jackson.databind.ObjectMapper;
ObjectMapper mapper = new ObjectMapper();
Object obj = mapper.readValue(theString, Object.class);
That seems to do exactly what I want. And it's so obvious too!

Another option should you decide to ditch Jackson (Jackson is fine, I'm quite agnostic in the JSON wars) is json-simple.
JSONObject jObject = JSONValue.parse(String jsonString);
Since JSONObject extends java.util.HashMap everything should work.

What is the the best way to convert JSONObject to a domain object?

I have a rest service returning some data. I use Restlet client api as shown below to access this service. As you can see, it returns org.json.JSONObject. Is there a easy way to map this to the domain object (may be through annotations?) or should I have to write code to create the domain object?
Representation entity = new ClientResource(uri).get();
JSONObject json = new JsonRepresentation(entity).getJsonObject();

May be you can leverage from Gson library which has a function you need:
// Convert JSON into Java object
SomeObj obj = gson.fromJson(jsonObjStr, SomeObj.class)
You can read more here...

While there are decent APIs for easily mapping between Java data structures, e.g., from the JSONObject to your preferred data structure, since the incoming data format is JSON, I'd much prefer to just use a good JSON-to/from-Java API like Jackson. Depending on the preferred transformation details, the solution might be just one simple line of code with such an API.