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Java Spring - How to get one specific key value from a very nested json without mapping to a specific pojo?

Small java and spring question regarding how to get a specific key value from a very nested json, without having to map back to java pojos please.
I am consuming an api, where the json response is gigantic. The raw response does not fit in a screen.
The response is also very nested. Meaning, it has fields inside fields inside fields... etc
I have no access, no way to modify this API.
Nonetheless, it is a very interesting API, and in this very gigantic payload, very nested, there is always exactly one "the-key-i-need": "the-value-i-need",
Furthermore, there is no way to know in advanced how nested (which layer, which child) and no way to know where will "the-key-i-need": "the-value-i-need", be.
Also, there is no way to map the response back to any POJO, it changes always, the only information, "the-key-i-need": "the-value-i-need", exists, and it is always there.
I am well aware of GSON or fasterxml libraries, that can help map the json string back to existing pojos.
However, in my case, such will not help, since the existing pojo does not exists. the response is always different, the structure, the level of nesting is always different.
My question is, instead of trying to map back to pojos that will always change, and very nested, is there a simpler way, to just use some kind of regex, or something else, to extract the key value, "the-key-i-need": "the-value-i-need", and only this please?
I already tried mapping to all kinds of pojos, and unfortunately the response structure is too dynamic.
Thank you

Since you're using Spring, you very likely already have Jackson FasterXML in you classpath.
Normally, Spring uses the Databind module, which relies on the Streaming module, aka the Core module.
In this case, you want to use Streaming directly, so get the JSON text as a String, and start the parser.
static String getFieldValue(String json, String field) throws JsonParseException, IOException {
JsonFactory factory = new JsonFactory();
try (JsonParser parser = factory.createParser(json)) {
for (JsonToken token; (token = parser.nextToken()) != null; ) {
if (token == JsonToken.FIELD_NAME && parser.getCurrentName().equals(field)) {
token = parser.nextToken();
// check token here if object or array should throw exception instead of returning null
return parser.getValueAsString();
}
}
}
return null; // or throw exception if "not found" shouldn't return null
}
Test
String json = "{ \"A\": { \"B\": [ 5, { \"C\": \"D\" }, true ], \"E\": null, \"F\": 42, \"G\": false }}";
System.out.println("C: " + getFieldValue(json, "C")); // "D"
System.out.println("E: " + getFieldValue(json, "E")); // null (null-value)
System.out.println("F: " + getFieldValue(json, "F")); // "42"
System.out.println("G: " + getFieldValue(json, "G")); // "false"
System.out.println("H: " + getFieldValue(json, "H")); // null (not found)
System.out.println("B: " + getFieldValue(json, "B")); // null (not a value)

JsonPath
If using an external library is an option, then JsonPath might help.
Maven
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.5.0</version>
</dependency>
StackOverflow Tag for JsonPath
Example usage as shared in the README
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century"
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
},
"expensive": 10
}
To access all the author names
List<String> authors = JsonPath.read(json, "$..author");
System.out.println(authors);
Output
["Nigel Rees","Evelyn Waugh"]
To access all the prices (across both book and bicycle)
List<Double> prices = JsonPath.read(json, "$..price");
System.out.println(prices);
Output
[12.99, 19.95]
Note
Some missing keys can cause remapping extracted data across two fields difficult
Say fetching category and price from the above example will make it difficult to summarize a category to price mapping
List<String> categories = JsonPath.read(json, "$..category");
System.out.println(categories);
Output
["reference", "fiction"]
Based on the above example, price and category does not have correct 1-1 mapping

How to convert value with unicode in Json request into simple characters?

Sometime client send Json-RPC request with Json value as unicorde symboles.
Example:
{ "jsonrpc": "2.0", "method": "add", "params": { "fields": [ { "id": 1, "val": "\u0414\u0435\u043d\u0438\u0441" }, { "id": 2, "val": "\u041c\u043e\u044f" } ] }, "id": "564b0f7d-868a-4ff0-9703-17e4f768699d" }
How do I processing Json-RPC request:
My server get the request like byte[];
Convert it to io.vertx.core.json.JsonObject;
Make some manipulations;
Save to DB;
And I found in DB records like:
"val": "\u0414\u0435\u043d\u0438\u0441"
And the worst in this story. If client try to search this data, he'll get:
"val": "\\u0414\\u0435\\u043d\\u0438\\u0441"
So I think, that I need to convert request data before deserialization to JsonObject.
I tried and it didn't help:
String json = new String(incomingJsonBytes, StandardCharsets.UTF_8);
return json.getBytes(StandardCharsets.UTF_8);
Also I tried to use StandardCharsets.US_ASCII.
Note: Variant with StringEscapeUtils.unescapeJava() I can not, because it unescape all necessary and unnecessary '\' symbols.
If anyone know how to solve it? Or library that already makes it?
Thank a lot.

io.vertx.core.json.JsonObject depends on Jackson ObjectMapper to perform the actual JSON deserialization (e.g. io.vertx.core.json.Json has a ObjectMapper field). By default Jackson will convert \u0414\u0435\u043d\u0438\u0441 into Денис. You can verify this with a simple code snippet:
String json = "{ \"jsonrpc\": \"2.0\", \"method\": \"add\", \"params\": { \"fields\": [ { \"id\": 1, \"val\": \"\\u0414\\u0435\\u043d\\u0438\\u0441\" }, { \"id\": 2, \"val\": \"\\u041c\\u043e\\u044f\" } ] }, \"id\": \"564b0f7d-868a-4ff0-9703-17e4f768699d\" }";
ObjectMapper mapper = new ObjectMapper();
Map map = mapper.readValue(json, Map.class);
System.out.println(map); // {jsonrpc=2.0, method=add, params={fields=[{id=1, val=Денис}, {id=2, val=Моя}]}, id=564b0f7d-868a-4ff0-9703-17e4f768699d}
Most likely the client is sending something else because your example value is deserialized correctly. Perhaps it's doubly escaped \\u0414\\u0435\\u043d\\u0438\\u0441 value which Jackson will convert to \u0414\u0435\u043d\u0438\u0441 removing one layer of escaping?
There is no magic solution for this. Either write your own Jackson deserialization configuration or make the client stop sending garbage.

How to convert a file to a String which is accepted in JSON?

I am trying to create gists in Github via REST ASSURED.
To create a gist a need to pass file names and their contents.
Now, the content of the file is something which is being rejected by the API.
Example:
{
"description": "Hello World Examples",
"public": true,
"files": {
"hello_world.rb": {
"content": "class HelloWorld\n def initialize(name)\n #name = name.capitalize\n end\n def sayHi\n puts \"Hello !\"\n end\nend\n\nhello = HelloWorld.new(\"World\")\nhello.sayHi"
},
"hello_world.py": {
"content": "class HelloWorld:\n\n def init(self, name):\n self.name = name.capitalize()\n \n def sayHi(self):\n print \"Hello \" + self.name + \"!\"\n\nhello = HelloWorld(\"world\")\nhello.sayHi()"
},
"hello_world_ruby.txt": {
"content": "Run ruby hello_world.rb to print Hello World"
},
"hello_world_python.txt": {
"content": "Run python hello_world.py to print Hello World"
}
}
This is how the the API wants the JSON to be, I could get this via my code:
{
"description": "Happy World",
"public": true,
"files": {
"sid.java": {
"content": "Ce4z5e22ta"
},
"siddharth.py": {
"content": "def a:
if sidh>kundu:
sid==kundu
else:
kundu==sid
"
}
}
}
So the change in the indentations is causing GitHUb API to fail this with 400 error. Can someone please help?

As pointed out in the comments, JSON does not allow control characters in strings. In the case of line breaks, these were encoded as \n in the example.
You should definitely consider using a proper library to create the JSON rather than handling the raw strings yourself.

Create a POJO which will represent your gist (i.e. object with fields like 'description', 'files' collection. And separate POJO for file containing string fields 'name' and 'content';
Do something like this to convert your gist:
try {
GistFile file new GistFile();// Assuming this is POJO for your file
//Set name and content
Gist gist = new Gist(); //Asuming this is a POJO for your gist
gist.addFile(file);
//Add more files if needed and set other properties
ObjectMapper mapper = new ObjectMapper();
String content = mapper.writeValueAsString(gist);
//Now you have valid JSON string
} catch (Exception e) {
e.printStackTrace();
}
This is for com.fasterxml.jackson.databind.ObjectMapper or use different JSON library
Actually there are GitHub specific libraries which do most of the job for you. Please refer to this question: How to connect to github using Java Program it might be helpful

java native JSON api for parsing

I've following JSON structure coming in,
{
"name": "product new",
"brand": {
"id": 1
},
"category": {
"id": 1
}
}
I can extract
jsonObject = Json.createReader(httpServletRequest.getInputStream()).readObject();
jsonObject.getString("name")
Errors:
jsonObject.getInt("brand.id")
jsonObject.getInt("category.id")
I'm using Java API for JSON.
Edit If I access
System.out.println(jsonObject.get("brand"));
// response {"id":1}
System.out.println(jsonObject.get("brand.id"));
// null
http://www.oracle.com/technetwork/articles/java/json-1973242.html

I don't think the API you're using supports nested expressions. You'll need to access the parent object, and then the specific field:
System.out.println(jsonObject.getJsonObject("brand").getInt("id"));
Or you can use an API that accepts a path expression, like Jackson:
JsonNode node = new ObjectMapper().readTree(httpServletRequest.getInputStream());
System.out.println(node.at("/brand/id").asInt());

Issue with serializing single-element ArrayList to JSON

I am writing Junit test case for my REST service, i am setting the values(below is the piece of code) to get the payload required for REST service
Payload jsonPayload = new Payload ();
payload.setAcc("A");
List<Details> details= new ArrayList<Details>;
Details detail = new Details();
detail.setTotalAmount(1);
detail.setCurrency("dollar");
details.add(detail);
payload.getDetails().addAll(details);
I want JSON to be built in format mentioned below, but I am not getting the JSON as expected, details should be in form of Array.
Required JSON -
{
"Acc" : "A",
"details": [
{
"totalAmount":1,
"currency":"dollar"
}
]
}
Output JSON -
{
"Acc" : "A",
"details":
{
"totalAmount":1,
"currency":"dollar"
}
}
Can anyone help me how can I achieve this?