Using JsonPath expressions
JSON stands for JavaScript Object Notation. It's a lightweight data format to exchange data. JsonPath is a query language for JSON, similar to XPath for XML.
JsonPath expressions always refer to a JSON structure in the same way as XPath expressions are used in combination with an XML document. The "root member object" in JsonPath is always referred to as $ regardless if it is an object or array.
JsonPath is supported by the following components:
Selecting nodes
JsonPath expressions use dot–notation, for example $.store.book[0].title.
Alternatively bracket–notation like $['store']['book'][0]['title'] can be used.
Use the bracket-notation if a JSON key contains spaces, for example: $['JSON key with spaces'].
Operators
Use the operators below to select elements in a JSON.
| Operator | Description |
|---|---|
$ | The root element to query. This starts all path expressions. |
@ | The current node being processed by a filter predicate. |
* | Wildcard. Available anywhere a name or numeric are required. |
.. | Deep scan. Available anywhere a name is required. |
.<name> | Dot-notated child |
['<name>' (, '<name>')] | Bracket-notated child or children |
[<number> (, <number>)] | Array index or indexes |
[start:end] | Array slice operator |
[?(<expression>)] | Filter expression. Expression must evaluate to a boolean value. |
Functions
Functions can be invoked at the tail end of a path - the input to a function is the output of the path expression. The function output is dictated by the function itself.
| Function | Description | Output type |
|---|---|---|
min() | Provides the min value of an array of numbers | Double |
max() | Provides the max value of an array of numbers | Double |
avg() | Provides the average value of an array of numbers | Double |
stddev() | Provides the standard deviation value of an array of numbers | Double |
length() | Provides the length of an array | Integer |
sum() | Provides the sum value of an array of numbers | Double |
keys() | Provides the property keys (An alternative for terminal tilde ~) | Set<E> |
concat(X) | Provides a concatinated version of the path output with a new item | like input |
append(X) | add an item to the json path output array | like input |
first() | Provides the first item of an array | Depends on the array |
last() | Provides the last item of an array | Depends on the array |
index(X) | Provides the item of an array of index: X, if the X is negative, take from backwards | Depends on the array |
Filter Operators
Filters are logical expressions used to filter arrays. A typical filter would be [?(@.age > 18)] where @ represents the current item being processed. More complex filters can be created with logical operators && and ||. String literals must be enclosed by single or double quotes ([?(@.color == 'blue')] or [?(@.color == "blue")]).
| Operator | Description |
|---|---|
== | left is equal to right (note that 1 is not equal to '1') |
!= | left is not equal to right |
< | left is less than right |
<= | left is less or equal to right |
> | left is greater than right |
>= | left is greater than or equal to right |
=~ | left matches regular expression [?(@.name =~ /foo.*?/i)] |
in | left exists in right [?(@.size in ['S', 'M'])] |
nin | left does not exists in right |
subsetof | left is a subset of right [?(@.sizes subsetof ['S', 'M', 'L'])] |
anyof | left has an intersection with right [?(@.sizes anyof ['M', 'L'])] |
noneof | left has no intersection with right [?(@.sizes noneof ['M', 'L'])] |
size | size of left (array or string) should match right |
empty | left (array or string) should be empty |
Examples
This JSON is used in the examples below.
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
},
"expensive": 10
}
| JsonPath example | Result |
|---|---|
$.store.book[*].author | The authors of all books |
$..author | All authors |
$.store.* | All things, both books and bicycles |
$.store..price | The price of everything |
$..book[2] | The third book |
$..book[-2] | The second to last book |
$..book[0,1] | The first two books |
$..book[:2] | All books from index 0 (inclusive) until index 2 (exclusive) |
$..book[1:2] | All books from index 1 (inclusive) until index 2 (exclusive) |
$..book[-2:] | Last two books |
$..book[2:] | All books from index 2 (inclusive) to last |
$..book[?(@.isbn)] | All books with an ISBN number |
$.store.book[?(@.price < 10)] | All books in store cheaper than 10 |
$..book[?(@.price <= $['expensive'])] | All books in store that are not "expensive" |
$..book[?(@.author =~ /.*REES/i)] | All books matching regex (ignore case) |
$..* | Give me everything |
$..book.length() | The number of books |
Useful references
For more detailed information go to: