I am looking at extracting the root element of a JSON document. It looks like this is possible neither using JsonPointer nor JsonPath as my attempts to look up for such an expression has been unsuccessful. Any tips would be appreciated. TIA.
Sample document:
{
"MESSAGE1_ROOT_INPUT": {
"CTRL_SEG": "test"
}
}
The below using gson 2.9.0:
$.*~
produces:
{"CTRL_SEG": "test"}
while JSONPath Online produces this:
[
"MESSAGE1_ROOT_INPUT"
]
The attempt is to get text "MESSAGE1_ROOT_INPUT" using JsonPath/JsonPointer expression(s). Note that, extracting this the traditional (substring or regex on a stringified json text) way, would preferably be my last resort.
Background: We are building an API service that accepts JSON documents with different roots. Such as, MESSAGE2_ROOT_INPUT, MESSAGE3_ROOT_INPUT, etc. It is based on this, the routing of a message further will occur.
Supported/Employed Languages: Java/GSON Library/RegEx
Gson does not natively support JSONPath or JSON Pointer. However, you can quite efficiently obtain the name of the first property using JsonReader:
public static String getFirstPropertyName(Reader reader) throws IOException {
// Don't have to call JsonReader.close(); that would just close the provided reader
JsonReader jsonReader = new JsonReader(reader);
jsonReader.beginObject();
return jsonReader.nextName();
}
There are however two things to keep in mind:
This only reads the beginning of the JSON document; it neither verifies that the complete JSON document has valid syntax, nor checks if there might be more top-level properties
This consumes some data from the Reader; to further process the data you have to buffer the data to allow re-reading it again (you can also first store the JSON in a String and pass a StringReader to JsonReader)
Related
I'm using Flink to process the data coming from some data source (such as Kafka, Pravega etc).
In my case, the data source is Pravega, which provided me a flink connector.
My data source is sending me some JSON data as below:
{"key": "value"}
{"key": "value2"}
{"key": "value3"}
...
...
Here is my piece of code:
PravegaDeserializationSchema<ObjectNode> adapter = new PravegaDeserializationSchema<>(ObjectNode.class, new JavaSerializer<>());
FlinkPravegaReader<ObjectNode> source = FlinkPravegaReader.<ObjectNode>builder()
.withPravegaConfig(pravegaConfig)
.forStream(stream)
.withDeserializationSchema(adapter)
.build();
final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<ObjectNode> dataStream = env.addSource(source).name("Pravega Stream");
dataStream.map(new MapFunction<ObjectNode, String>() {
#Override
public String map(ObjectNode node) throws Exception {
return node.toString();
}
})
.keyBy("word") // ERROR
.timeWindow(Time.seconds(10))
.sum("count");
As you see, I used the FlinkPravegaReader and a proper deserializer to get the JSON stream coming from Pravega.
Then I try to transform the JSON data into a String, KeyBy them and count them.
However, I get an error:
The program finished with the following exception:
Field expression must be equal to '*' or '_' for non-composite types.
org.apache.flink.api.common.operators.Keys$ExpressionKeys.<init>(Keys.java:342)
org.apache.flink.streaming.api.datastream.DataStream.keyBy(DataStream.java:340)
myflink.StreamingJob.main(StreamingJob.java:114)
It seems that KeyBy threw this exception.
Well, I'm not a Flink expert so I don't know why. I've read the source code of the official example WordCount. In that example, there is a custtom splitter, which is used to split the String data into words.
So I'm thinking if I need to use some kind of splitter in this case too? If so, what kind of splitter should I use? Can you show me an example? If not, why did I get such an error and how to solve it?
I guess you have read the document about how to specify keys
Specify keys
The example codes use keyby("word") because word is a field of POJO type WC.
// some ordinary POJO (Plain old Java Object)
public class WC {
public String word;
public int count;
}
DataStream<WC> words = // [...]
DataStream<WC> wordCounts = words.keyBy("word").window(/*window specification*/);
In your case, you put a map operator before keyBy, and the output of this map operator is a string. So there is obviously no word field in your case. If you actually want to group this string stream, you need to write it like this .keyBy(String::toString)
Or you can even implement a customized keySelector to generate your own key.
Customized Key Selector
I want to write an API ReST endpoint, using Spring 4.0 and Groovy, such that the #RequestBody parameter can be any generic JSON input, and it will be mapped to a Groovy JsonSlurper so that I can simply access the data via the slurper.
The benefit here being that I can send various JSON documents to my endpoint without having to define a DTO object for every format that I might send.
Currently my method looks like this (and works):
#RequestMapping(value = "/{id}", method = RequestMethod.PUT, consumes = MediaType.APPLICATION_JSON_VALUE)
ResponseEntity<String> putTest(#RequestBody ExampleDTO dto) {
def json = new groovy.json.JsonBuilder()
json(
id: dto.id,
name: dto.name
);
return new ResponseEntity(json.content, HttpStatus.OK);
}
But what I want, is to get rid of the "ExampleDTO" object, and just have any JSON that is passed in get mapped straight into a JsonSlurper, or something that I can input into a JsonSlurper, so that I can access the fields of the input object like so:
def json = new JsonSlurper().parseText(input);
String exampleName = json.name;
I initially thought I could just accept a String instead of ExampleDTO, and then slurp the String, but then I have been running into a plethora of issues in my AngularJS client, trying to send my JSON objects as strings to the API endpoint. I'm met with an annoying need to escape all of the double quotes and surround the entire JSON string with double quotes. Then I run into issues if any of my data has quotes or various special characters in it. It just doesn't seem like a clean or reliable solution.
I open to anything that will cleanly translate my AngularJS JSON objects into valid Strings, or anything I can do in the ReST method that will allow JSON input without mapping it to a specific object.
Thanks in advance!
Tonya
I'm trying to build a restful API and I'm struggling on how to serialize JSON data to a HTTP query string.
There are a number of mandatory and optional arguments that need to be passed in the request, e.g (represented as a JSON object below):
{
"-columns" : [
"name",
"column"
],
"-where" : {
"-or" : {
"customer_id" : 1,
"services" : "schedule"
}
},
"-limit" : 5,
"return" : "table"
}
I need to support a various number of different clients so I'm looking for a standardized way to convert this json object to a query string. Is there one, and how does it look?
Another alternative is to allow users to just pass along the json object in a message body, but I read that I should avoid it (HTTP GET with request body).
Any thoughts?
Edit for clarification:
Listing how some different languages encodes the given json object above:
jQuery using $.param: -columns[]=name&-columns[]=column&-where[-or][customer_id]=1&-where[-or][services]=schedule&-limit=5&return=column
PHP using http_build_query: -columns[0]=name&-columns[1]=column&-where[-or][customer_id]=1&-where[-or][services]=schedule&-limit=5&return=column
Perl using URI::query_form: -columns=name&-columns=column&-where=HASH(0x59d6eb8)&-limit=5&return=column
Perl using complex_to_query: -columns:0=name&-columns:1=column&-limit=5&-where.-or.customer_id=1&-where.-or.services=schedule&return=column
jQuery and PHP is very similar. Perl using complex_to_query is also pretty similar to them. But none look exactly the same.
URL-encode (https://en.wikipedia.org/wiki/Percent-encoding) your JSON text and put it into a single query string parameter. for example, if you want to pass {"val": 1}:
mysite.com/path?json=%7B%22val%22%3A%201%7D
Note that if your JSON gets too long then you will run into a URL length limitation problem. In which case I would use POST with a body (yes, I know, sending a POST when you want to fetch something is not "pure" and does not fit well into the REST paradigm, but neither is your domain specific JSON-based query language).
There is no single standard for JSON to query string serialization, so I made a comparison of some JSON serializers and the results are as follows:
JSON: {"_id":"5973782bdb9a930533b05cb2","isActive":true,"balance":"$1,446.35","age":32,"name":"Logan Keller","email":"logankeller#artiq.com","phone":"+1 (952) 533-2258","friends":[{"id":0,"name":"Colon Salazar"},{"id":1,"name":"French Mcneil"},{"id":2,"name":"Carol Martin"}],"favoriteFruit":"banana"}
Rison: (_id:'5973782bdb9a930533b05cb2',age:32,balance:'$1,446.35',email:'logankeller#artiq.com',favoriteFruit:banana,friends:!((id:0,name:'Colon Salazar'),(id:1,name:'French Mcneil'),(id:2,name:'Carol Martin')),isActive:!t,name:'Logan Keller',phone:'+1 (952) 533-2258')
O-Rison: _id:'5973782bdb9a930533b05cb2',age:32,balance:'$1,446.35',email:'logankeller#artiq.com',favoriteFruit:banana,friends:!((id:0,name:'Colon Salazar'),(id:1,name:'French Mcneil'),(id:2,name:'Carol Martin')),isActive:!t,name:'Logan Keller',phone:'+1 (952) 533-2258'
JSURL: ~(_id~'5973782bdb9a930533b05cb2~isActive~true~balance~'!1*2c446.35~age~32~name~'Logan*20Keller~email~'logankeller*40artiq.com~phone~'*2b1*20*28952*29*20533-2258~friends~(~(id~0~name~'Colon*20Salazar)~(id~1~name~'French*20Mcneil)~(id~2~name~'Carol*20Martin))~favoriteFruit~'banana)
QS: _id=5973782bdb9a930533b05cb2&isActive=true&balance=$1,446.35&age=32&name=Logan Keller&email=logankeller#artiq.com&phone=+1 (952) 533-2258&friends[0][id]=0&friends[0][name]=Colon Salazar&friends[1][id]=1&friends[1][name]=French Mcneil&friends[2][id]=2&friends[2][name]=Carol Martin&favoriteFruit=banana
URLON: $_id=5973782bdb9a930533b05cb2&isActive:true&balance=$1,446.35&age:32&name=Logan%20Keller&email=logankeller#artiq.com&phone=+1%20(952)%20533-2258&friends#$id:0&name=Colon%20Salazar;&$id:1&name=French%20Mcneil;&$id:2&name=Carol%20Martin;;&favoriteFruit=banana
QS-JSON: isActive=true&balance=%241%2C446.35&age=32&name=Logan+Keller&email=logankeller%40artiq.com&phone=%2B1+(952)+533-2258&friends(0).id=0&friends(0).name=Colon+Salazar&friends(1).id=1&friends(1).name=French+Mcneil&friends(2).id=2&friends(2).name=Carol+Martin&favoriteFruit=banana
The shortest among them is URL Object Notation.
How about you try this sending them as follows:
http://example.com/api/wtf?
[-columns][]=name&
[-columns][]=column&
[-where][-or][customer_id]=1&
[-where][-or][services]=schedule&
[-limit]=5&
[return]=table&
I tried with a REST Client
And on the server side (Ruby with Sinatra) I checked the params, it gives me exactly what you want. :-)
Another option might be node-querystring. It also uses a similar scheme to the ones you've so far listed.
It's available in both npm and bower, which is why I have been using it.
Works well for nested objects.
Passing complex objects as query parameters of a url.
In the example below, obj is the JSON object to pass into query parameters.
Injecting JSON object as query parameters:
value = JSON.stringify(obj);
URLSearchParams to convert a string to an object representing search params. toString to retain string type for appending to url:
queryParams = new URLSearchParams(value).toString();
Pass the query parameters using template literals:
url = `https://some-url.com?key=${queryParams}`;
Now url will contain the JSON object as query parameters under key (user-defined name)
Extracing JSON from url:
This is assuming you have access to the url (either as string or URL object)
url_obj = new URL(url); (only if url is NOT a URL object, otherwise ignore this step)
Extract all query parameters in the url:
queryParams = new URLSearchParams(url_obj.search);
Use the key to extract the specific value:
obj = JSON.parse(queryParams.get('key').slice(0, -1));
slice() is used to extract a tailing = in the query params which is not required.
Here obj will be the same object passed in the query params.
I recommend to try these steps in the web console to understand better.
You can test with JSON examples here: https://json.org/example.html
I am trying to parse some JSON objects which is made just of (string,string) pairs, in order to emulate Resjson behaviour. The file I am parsing contains this.
{
"greeting":"Hello world",
"_greeting.comment":"Hello comment.",
"_greeting.source":"Original Hello",
}
Please note the last comma is incorrect, and I also used http://jsonlint.com/ to test JSON syntax. It tells me it is incorrect, as I expected. My - slightly modified - code is :
string path = #"d:\resjson\example.resjson";
string jsonText = File.ReadAllText(path);
IDictionary<string, string> dict;
try
{
dict = JsonConvert.DeserializeObject<IDictionary<string, string>>(jsonText);
}
catch(Exception ex)
{
// code never reaches here
}
My above code returns the IDictionary with the 3 keys as if the formatting was correct. If I serialize back, the string obtained is without the last comma.
My questions are :
Is Newtonsoft.Json so permissive that it allows users slight errors ?
If so, can I set the permissiveness so that it is more strict ?
Is there a way to check if a string is valid JSON format, using
Newtonsoft.Json with and/or without the permissiveness?
what is the difference between json string and parsed json string?
for eg in javascript suppose i have a string in the json format say [{},{}]
parsing this string will also produce the same thing.
So why do we need to parse?
It's just serialization/deserialization.
In Javscript code you normally work with the object, as that lets you easily get its properties, etc, while a JSON string doesn't do you much good.
var jsonobj = { "arr": [ 5, 2 ], "str": "foo" };
console.log(jsonobj.arr[1] + jsonobj.str);
// 2foo
var jsonstr = JSON.stringify(jsonobj);
// cannot do much with this
To send it to the server via an Ajax call, though, you need to serialize (stringify) it first. Likewise, you need to deserialize (parse) from a string into an object when receiving JSON back from the server.
Great question. The difference is transfer format.
JSON is only the 'Notation' of a JavaScript Object, it is not actually the JavaScript 'object-literal' itself. So as the data is received in JSON, it is just a string to be interpreted, evaluated, parsed, in order to become an actual JavaScript 'Object-Literal.
There is one physical difference between the two, and that is quotation marks. It makes sense, that JSON needs to be a string to be transferred. Here is how:
//A JavaScript Object-Literal
var anObj = { member: 'value'}
//A JSON representation of that object
var aJSON = { "member":"value" }
Hope that helps. All the best! Nash
I think a parsed json string should be the string data into the actual javascript objects and data arrays (or whichever language the json string contains)
The JSON object contains methods for parsing JSON and converting values to JSON.
It can't be called or constructed, and aside from its two method properties it has no interesting functionality of its own.
JSONParser parser = new JSONParser();
Object object = parser.parse(Message.toString());
JSONObject arObj = (JSONObject) object;