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Parsing a subset of JSON in Java using Jackson

Given a Json, is it possible to use Jackson to only parse out a section of the message?
Say that the data I'm interested in is buried in a deep hierarchy of fields and I simply do not care about creating DTO classes for each and every class.
Given a very simplified scenario I'd like to model the Telephone class without knowing anything about the structure before it:
...{
"firstName": "John",
"lastName" : "doe",
"age" : 26,
"address" : {
"streetAddress": "naist street",
"city" : "Nara",
"postalCode" : "630-0192"
},
"phoneNumbers": [
{
"type" : "iPhone",
"number": "0123-4567-8888"
},
{
"type" : "home",
"number": "0123-4567-8910"
}
]
}....
I'm thinking something in the terms of using json-path together with deserializing just the parts I'm interested of. Some pseudo:
List<Telephone> phoneNrs = parse(".my.deep.structure.persons.phoneNumbers", List<Telephone.class>);

ObjectMapper mapper = new ObjectMapper();
JsonNode json = mapper.readTree("... your JSON ...");
Using the JsonNode object you can then call get("my").get("deep").get("structure") to get the node you want.
Once you got your hands on that node, a simple call to mapper.treeToValue(myDeepJsonNode, Telephone[].class) will get you your array ofTelephone. You can get a list using a TypeReference as well.
To get to your deep JsonNode you can also use the findValue and findPath methods.
The Javadoc:
https://fasterxml.github.io/jackson-databind/javadoc/2.2.0/com/fasterxml/jackson/databind/JsonNode.html

Yes, it is possible the way you have mentioned in the Pseudo code. "phoneNumbers" is a key and value returned can be passed on to Jackson deserialiying.
If the response is an array of maps then you can iterate through each one of them and use the yourResponseAsJSONObject.get('phoneNumbers') method to get the value and pass it on to Jackson
or use JsonPath as mentioned by #dimas

You can use JsonPath library. With this library you can map your JsonPath output directly into POJO's.
Pseudo:
List<Telephone> phoneNrs = JsonPath.parse(json).read("$.my.deep.structure.persons.phoneNumbers", List.class);

To do this efficiently with Jackson, use the Streaming API via the JsonParser class (http://fasterxml.github.io/jackson-core/javadoc/2.5/com/fasterxml/jackson/core/JsonParser.html).
This approach will allocate no additional memory and will not incur the cost of deserializing values for all of the skipped data. Since the code will be much longer and more difficult to read than using Jackson's ObjectMapper, only do this if profiling shows unacceptable GC activity or CPU usage during parsing.
You can skip all of the nodes that you are uninterested in until you hit the "phoneNumbers" key. Then you can call the readValueAs function to deserialize the array of phone number dictionaries like so readValueAs(new TypeReference<MyPhoneNumberType[]>()).
See also:
a tutorial on reading and writing with JsonParser: http://www.cowtowncoder.com/blog/archives/2009/01/entry_132.html
The main documentation: https://github.com/FasterXML/jackson-core

How to extract one substring from one Java Object in python?

I've a String like this:
["[Ljava.lang.Object;",[["Object0",{"key0": null, "coolKey1": "coolValue", "notCoolKey2":"something"}],["Object1",{"key3": "value1", "key4": "nonCoolValue", "Id":"importantId0", "someId":"importantId1"}],false,["Object3",{"key6": "value6", "nonkey7": "supercoolValue"}]]]
what I'm interested is these two key-value pairs:
Id:importantId0 and someId:importantId1
How can I extract these two key value pairs from this String in Python?
I've tried to use STRING.spit("DELIMITER"), but failed, any help is greatly appreciated!

That looks to be a JSON serialization and so you should use the json module to convert it to a Python object, then access the data you need from it.
import json
x = json.loads("""["[Ljava.lang.Object;",[["Object0",{"key0": null, "coolKey1": "coolValue",
"notCoolKey2":"something"}],["Object1",{"key3": "value1", "key4": "nonCoolValue",
"Id":"importantId0", "someId":"importantId1"}],false,["Object3", {"key6": "value6",
"nonkey7": "supercoolValue"}]]]""")
print x[1][1][1]["Id"]
print x[1][1][1]["someId"]

Verify field value for each list item in a REST response

Let's say that we have the following json response:
{
"data":
[
{
"id": 1,
"name": "Pablo"
},
{
"id": 2,
"name": "Ernesto"
}
]
...
}
Where the data list could consist of many more objects. If I where to verify that no name field is set to null, what would be the Rest Assured way of doing this?
Now I'm using:
from(response.asString()).get("data");
to get a list of HashMaps, and then moving on from there for each entry. But I guess there is some other way that is more efficient?
Edit/Clarification: I am wondering if there is a way to do this without the creation of a list of maps?

i guess this is the best we can do
List<HashMap> data = from(response.asString()).get("data");
for(HashMap map: data){
if(map.get("name") == null){
// null name found
}
}
// No null name found

Ok, so perhaps I should have read the docs a bit more carefully, the easiest (and intended) way to retrieve e.g. all name values (as in my example) is to use JsonPath like so:
List<Object> names = from(response.asString()).get("data.name");
So there are no magical utility methods within the Rest-Assured library to do this except using JsonPath.from().get() and then to go from there.

I need to transform a JsonObject into a hashmap, but the structure of the JSON is a bit different

This is the structure of the JSON that I need to transform:
{
"United Kingdom": {
"visit_count": 2,
"cities": {
"London": 2
}
},
"Netherlands": {
"visit_count": 1182,
"cities": {
"Amsterdam": 441
}
}
}
Which is basically a JSonObject, which contains an array of objects, BUT the key is the name of the country, and the right part, are the properties of the object. The same goes for the "Cities" JsonObject.
Now I tried doing this with jsonschema2pojo, but it tries to create objects after the name of the countries (United Kingdom, Netherlads) when this objects are actually the same type.
I was thinking of somehow loading the json into a hashmap, but don't know how exactly to do that. Is is possible?

Use google's Gson, it works excellent.
https://code.google.com/p/google-gson/
And take a look into here

You can try to use JSON-simple library: https://code.google.com/p/json-simple/
JSONObjects parsed by this library are literally represented as a HashMap. (org.json.simple.JSONObject extends HashMap) :-)

Parsing this JSON with Java?

When Parsing JSON I normally just constuct an object and use the gsonlibrary to parse my String into that object.
However, I now find myself with a rather complex response which consists of many elements each with sub elements of objects and arrays and arrays of objects. It looks something like this...
{
"type": "thetype",
"object":{
"text": "texthere",
"moretext": "more here"
},
...,
...,
...,
...,
"fieldIwant": [
{
"object":"object!"
},
....
....
{
"object":"object!"
},
]
}
The thing is, I'm only really interested in fieldIwantand nothing else. Is there not a way in Java for me to just extract that field and work with it alone and not all this other dead weight I do not need?

According to this http://sites.google.com/site/gson/gson-design-document it looks like gson does this for you by default.
When you are deserializing a Json string into an object of desired type, you can either navigate the tree of the input, or the type tree of the desired type. Gson uses the latter approach of navigating the type of the target object. This keeps you in tight control of instantiating only the type of objects that you are expecting (essentially validating the input against the expected "schema"). By doing this, you also ignore any extra fields that the Json input has but were not expected.
In other words, it doesn't deserialize any of the fields you don't need. You should be good to go.

You can use the low level JsonParser API
JsonObject jsonObject = new JsonParser().parse(json).getAsJsonObject();
yourArray = new Gson().fromJson(jsonObject.get("fieldIwant"), yourArrayType);
Alternatively you can create an ExclusionStrategy to use with a GsonBuilder