In a JSON API, is it valid to return single values such as 123, "somestring" or null?
I read the JSON spec, which states that:
JSON is built on two structures:
A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.
but I'm not clear if this means that only objects and arrays are valid JSON, or if values on their own are valid too (i.e. will be parsed correctly by any compliant parser).
Any idea?
No, it's not valid. Check this out if you want to experiment with anything.
The two structures are as follows:
Some kind of key-value pair:
{
"key": "value"
}
or an array
['value', 'value']
or any combination of the two
[{"key":"value"}, "value", ["a", "list", {"another":['list']}]]
However, the values on their own (numbers, strings, booleans, etc., are not valid on their own.
Is 123 a collection of name/value pairs? No, it is not.
Is 123 an ordered list of values? No, it is not.
Thus, 123 is not a valid JSON string.
Edit: As gdoron suggested, you could use a JSON parser (e.g. here) to test your single value.
Related
The json data structure for jstree is define in https://github.com/vakata/jstree, here is an example
[ { "text" : "Root node", "children" : [ "Child node 1", "Child node 2" ] } ]
Notably it says
The children key can be used to add children to the branch, it should
be an array
However later on in section Populating the tree using AJAX and lazy loading nodes it shows to use set children to false to indicate when a child has not be processed
[{
"id":1,"text":"Root node","children":[
{"id":2,"text":"Child node 1","children":true},
{"id":3,"text":"Child node 2"}
]
}]
So here we see children used as both as an array and as a boolean
I am using jstree as an example because this is where I encountered the issue, but my question is really a general json question. My question is this, is it valid JSON for the same element in json to be two different types (an array and a boolean)
Structure wise, both are valid JSON packets. This is okay, as JSON is somewhat less stricter than XML(with a XSD or a DTD). As per: https://www.w3schools.com/js/js_json_objects.asp,
JSON objects are surrounded by curly braces {}.
JSON objects are written in key/value pairs.
Keys must be strings, and values must be a valid JSON data type (string, number, object, array, boolean or null).
Keys and values are separated by a colon.
Each key/value pair is separated by a comma.
Having said that, if the sender is allowed to send such JSONs, only caveat is that server side will have to handle this discrepancy upon receiving such different packets. This is a bad-looking-contract, and hence server might need to do extra work to manage it. Server side handling of such incoming JSON packets can become tricky.
See: How do I create JSON data structure when element can be different types in for use by
You could validate whether a JSON is okay or not at https://jsonlint.com/
See more about JSON in this answer: https://stackoverflow.com/a/4862511/945214
It is valid Json. JSON RFC 8259 defines a general syntax but it contains nothing that would allow a tool to identify that two equally named entries are meant to describe the same conceptual thing.
The need to have a criteria to check two JSON structures for instance equality has been one motivation to create something like Json Schema.
I also think it is not too unusual for javascript to provide this kind of mixed data. Sometimes it might help to explicitly convert the javascript object to JSON. Like in JSON.stringify(testObject)
A thing for json validation
https://www.npmjs.com/package/json-validation
https://davidwalsh.name/json-validation.
Is the following valid JSON?
["start", 1234]
["open", 97]
I read the official standard twice and I wasn't able to find anything that said that this isn't valid JSON.
Interesting question. Couldn't help but research a bit. RFC-7159 explicitly refers to ECMA-404, which says:
A JSON value can be an object, array, number, string, true, false, or null
So basically, ECMA-404 tells us that a JSON value can be either of the above, but only a single one of them. Given your example:
["start", 1234]
["open", 97]
That'd not be considered valid JSON together, at it is not an array, but two arrays, and therefore two JSON values and not one.
What is the general format for a JSON file?
Is it a dictionary with 1 key whose value is a list of dictionaries (with each dictionary corresponding to a row)?
The general format of json is a key-value pair where each value may contain either a value, an array of values, or another set of key-value pairs.
As described on json.org:
JSON is built on two structures:
A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.
For example:
{"employees":[
{"firstName":"John", "lastName":"Doe"},
{"firstName":"Anna", "lastName":"Smith"},
{"firstName":"Peter", "lastName":"Jones"}
]}
Is this valid JSON?
{
"a" : [
"x",
"x"
]
}
http://jsonlint.com/ says yes.
http://www.json.org/ doesn't say anything about it being forbidden, but does say:
JSON is built on two structures:
A collection of name/value pairs. In various languages, this is realized as an object, record, struct, dictionary, hash table, keyed list, or associative array.
An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.
An ordered list of values. In most languages, this is realized as an array, vector, list, or sequence.
"An ordered list of values" suggests duplicates are therefore valid. Is this correct? Is there anything more explicit? Are there any JSON implementation which don't allow duplicate values?
(Here's the related question about duplicate keys.)
That is valid JSON. What is not allowed is having duplicate keys, such as:
{
"a": 1,
"a": 2
}
Also, by "ordered" I believe it refers to the fact that values have a predefined, well established order, not that they are sorted in any way :)
From what I can read on json.org, all JSON strings should start with { (curly brace), and [ characters (square brackets) represent an array element in JSON.
I use the json4j library, and I got an input that starts with [, so I didn't think this was valid JSON. I looked briefly at the JSON schema, but I couldn't really find it stated that a JSON file cannot start with [, or that it can only start with {.
JSON can be either an array or an object. Specifically off of json.org:
JSON is built on two structures:
A collection of name/value pairs. In various languages, this is
realized as an object, record,
struct, dictionary, hash table,
keyed list, or associative array.
An ordered list of values. In most languages, this is realized as an
array, vector, list, or sequence.
It then goes on to describe the two structures as:
Note that the starting and ending characters are curly brackets and square brackets respectively.
Edit
And from here: http://www.ietf.org/rfc/rfc4627.txt
A JSON text is a sequence of tokens.
The set of tokens includes six
structural characters, strings,
numbers, and three literal names.
A JSON text is a serialized object or array.
Update (2014)
As of March 2014, there is a new JSON RFC (7159) that modifies the definition slightly (see pages 4/5).
The definition per RFC 4627 was: JSON-text = object / array
This has been changed in RFC 7159 to: JSON-text = ws value ws
Where ws represents whitespace and value is defined as follows:
A JSON value MUST be an object, array, number, or string, or one of
the following three literal names:
false null true
So, the answer to the question is still yes, JSON text can start with a square bracket (i.e. an array). But in addition to objects and arrays, it can now also be a number, string or the values false, null or true.
Also, this has changed from my previous RFC 4627 quote (emphasis added):
A JSON text is a sequence of tokens. The set of tokens includes six
structural characters, strings, numbers, and three literal names.
A JSON text is a serialized value. Note that certain previous
specifications of JSON constrained a JSON text to be an object or an
array. Implementations that generate only objects or arrays where a
JSON text is called for will be interoperable in the sense that all
implementations will accept these as conforming JSON texts.
If the string you are parsing begins with a left brace ([) you can use JSONArray.parse to get back a JSONArray object and then you can use get(i) where i is an index from 0 through the returned JSONArray's size()-1.
import java.io.IOException;
import com.ibm.json.java.JSONArray;
import com.ibm.json.java.JSONObject;
public class BookListTest {
public static void main(String[] args) {
String jsonBookList = "{\"book_list\":{\"book\":[{\"title\":\"title 1\"},{\"title\":\"title 2\"}]}}";
Object book_list;
try {
book_list = JSONObject.parse(jsonBookList);
System.out.println(book_list);
Object bookList = JSONObject.parse(book_list.toString()).get("book_list");
System.out.println(bookList);
Object books = JSONObject.parse(bookList.toString()).get("book");
System.out.println(books);
JSONArray bookArray = JSONArray.parse(books.toString());
for (Object book : bookArray) {
System.out.println(book);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
Which produced output like:
{"book_list":{"book":[{"title":"title 1"},{"title":"title 2"}]}}
{"book":[{"title":"title 1"},{"title":"title 2"}]}
[{"title":"title 1"}, {"title":"title 2"}]
{"title":"title 1"}
{"title":"title 2"}
Note: if you attempted to call JSONObject.parse(books.toString()); you would get the error you encountered:
java.io.IOException: Expecting '{' on line 1, column 2 instead, obtained token: 'Token: ['
JSON.ORG WEBSITE SAYS ....
https://www.json.org/
The site clearly states the following:
JSON is built on two structures:
A collection of name/value pairs. In various languages, this is
realized as an object, record, struct, dictionary, hash table, keyed
list, or associative array.
An ordered list of values. In most languages, this is realized as
an array, vector, list, or sequence.
These are universal data structures. Virtually all modern programming languages support them in one form or another. It makes sense that a data format that is interchangeable with programming languages also be based on these structures.
In JSON, they take on these forms:
OBJECT:
An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).
{string: value, string: value}
ARRAY:
An array is an ordered collection of values. An array begins with [ (left bracket) and ends with ] (right bracket). Values are separated by , (comma).
[value, value, value ….]
VALUE:
A value can be a string in double quotes, or a number, or true or false or null, or an object or an array. These structures can be nested.
STRING:
A string is a sequence of zero or more Unicode characters, wrapped in double quotes, using backslash escapes. A character is represented as a single character string. A string is very much like a C or Java string.
NUMBER:
A number is very much like a C or Java number, except that the octal and hexadecimal formats are not used.
ABOUT WHITESPACE:
Whitespace can be inserted between any pair of tokens. Excepting a few encoding details, that completely describes the language.
Short answer is YES
In a .json file you can put Numbers (even just 10), Strings (even just "hello"), Booleans (true, false), Null (even just null), arrays and objects.
https://www.json.org/json-en.html
Using just Numbers, Strings, Booleans and Null are not logical because in .jon files we use more complicated structured data like arrays and object (mostly mix nested versions).
Below you can find a sample JSON data with array of object and start with "["
https://jsonplaceholder.typicode.com/posts