JsonPath
Getting Started
JsonPath is available at the Central Maven Repository. Maven users add
this to your POM.
If you need help ask questions at [Stack
Overflow]{.ul}. Tag
the question ‘jsonpath’ and ‘java’.
JsonPath expressions always refer to a JSON structure in the same way as
XPath expression 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 expressions can use the dot–notation
$.store.book[0].title
or the bracket–notation
$[‘store’][‘book’][0][‘title’]
Operators
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.
.
[‘
‘
[
[start:end] Array slice operator
[?(
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 Double
numbers
stddev() Provides the standard deviation value of an Double
array of numbers
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 Set
for terminal tilde ~)
concat(X) Provides a concatinated version of the path like input
output with a new item
append(X) add an item to the json path output array like input
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
Path Examples
Given the json
{
“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 (click link to try) Result
[[$.store.book[].author]{.ul}](http://jsonpath.herokuapp.com/?path=$.store.book%5b%5d.author) The authors of all books
[$..author]{.ul} All authors
[$.store.*]{.ul} All things, both books and bicycles
[$.store..price]{.ul} The price of everything
[[$..book[2]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b2%5d) The third book
[[$..book[-2]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b2%5d) The second to last book
[[$..book[0,1]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b0,1%5d) The first two books
[[$..book[:2]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b:2%5d) All books from index 0 (inclusive)
until index 2 (exclusive)
[[$..book[1:2]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b1:2%5d) All books from index 1 (inclusive)
until index 2 (exclusive)
[[$..book[-2:]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b-2:%5d) Last two books
[[$..book[2:]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b2:%5d) Book number two from tail
[[$..book[?(@.isbn)]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b?(@.isbn)%5d) All books with an ISBN number
[[$.store.book[?(@.price < 10)]]{.ul}](http://jsonpath.herokuapp.com/?path=$.store.book%5b?(@.price%20%3C%2010)%5d) All books in store cheaper than 10
[[$..book[?(@.price <= All books in store that are not
$[‘expensive’])]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b?(@.price%20%3C=%20$%5b%27expensive%27%5d)%5d) “expensive”
[[$..book[?(@.author =~ All books matching regex (ignore case)
/.*REES/i)]]{.ul}](http://jsonpath.herokuapp.com/?path=$..book%5b?(@.author%20=~%20/.*REES/i)%5d)
[$..*]{.ul} Give me every thing
[$..book.length()]{.ul} The number of books
Reading a Document
The simplest most straight forward way to use JsonPath is via the static
read API.
String json = “…”;
List
“$.store.book[*].author”);
If you only want to read once this is OK. In case you need to read an
other path as well this is not the way to go since the document will be
parsed every time you call JsonPath.read(…). To avoid the problem you
can parse the json first.
String json = “…”;
Object document =
Configuration.defaultConfiguration().jsonProvider().parse(json);
String author0 = JsonPath.read(document, “$.store.book[0].author”);
String author1 = JsonPath.read(document, “$.store.book[1].author”);
JsonPath also provides a fluent API. This is also the most flexible one.
String json = “…”;
ReadContext ctx = JsonPath.parse(json);
List
ctx.read(“$.store.book[?(@.isbn)].author”);
List<Map<String, Object>> expensiveBooks = JsonPath
.using(configuration)
.parse(json)
.read(“$.store.book[?(@.price > 10)]”, List.class);
What is Returned When?
When using JsonPath in java its important to know what type you expect
in your result. JsonPath will automatically try to cast the result to
the type expected by the invoker.
//Will throw an java.lang.ClassCastException
List
JsonPath.parse(json).read(“$.store.book[0].author”)
//Works fine
String author = JsonPath.parse(json).read(“$.store.book[0].author”)
When evaluating a path you need to understand the concept of when a path
is definite. A path is indefinite if it contains:
.. - a deep scan operator
?(
) - an expression [
, (, )] - multiple array indexes
Indefinite paths always returns a list (as represented by current
JsonProvider).
By default a simple object mapper is provided by the MappingProvider
SPI. This allows you to specify the return type you want and the
MappingProvider will try to perform the mapping. In the example below
mapping between Long and Date is demonstrated.
String json = “{“date_as_long” : 1411455611975}”;
Date date = JsonPath.parse(json).read(“$[‘date_as_long’]”,
Date.class);
If you configure JsonPath to
use JacksonMappingProvider or GsonMappingProvider you can even map your
JsonPath output directly into POJO’s.
Book book = JsonPath.parse(json).read(“$.store.book[0]”,
Book.class);
To obtain full generics type information, use TypeRef.
TypeRef<List
List
JsonPath.parse(JSON_DOCUMENT).read(“$.store.book[*].title”,
typeRef);
Predicates
There are three different ways to create filter predicates in JsonPath.
Inline Predicates
Inline predicates are the ones defined in the path.
List<Map<String, Object>> books = JsonPath.parse(json)
.read(“$.store.book[?(@.price < 10)]”);
You can use && and || to combine multiple predicates [?(@.price < 10
&& @.category == ‘fiction’)] , [?(@.category == ‘reference’ ||
@.price > 10)].
You can use ! to negate a predicate [?(!(@.price < 10 && @.category ==
‘fiction’))].
Filter Predicates
Predicates can be built using the Filter API as shown below:
import static com.jayway.jsonpath.JsonPath.parse;
import static com.jayway.jsonpath.Criteria.where;
import static com.jayway.jsonpath.Filter.filter;
…
…
Filter cheapFictionFilter = filter(
where(“category”).is(“fiction”).and(“price”).lte(10D)
);
List<Map<String, Object>> books =
parse(json).read(“$.store.book[?]”, cheapFictionFilter);
Notice the placeholder ? for the filter in the path. When multiple
filters are provided they are applied in order where the number of
placeholders must match the number of provided filters. You can specify
multiple predicate placeholders in one filter operation [?, ?], both
predicates must match.
Filters can also be combined with ‘OR’ and ‘AND’
Filter fooOrBar = filter(
where(“foo”).exists(true)).or(where(“bar”).exists(true)
);
Filter fooAndBar = filter(
where(“foo”).exists(true)).and(where(“bar”).exists(true)
);
Roll Your Own
Third option is to implement your own predicates
Predicate booksWithISBN = new Predicate() {
@Override
public boolean apply(PredicateContext ctx) {
return ctx.item(Map.class).containsKey(“isbn”);
}
};
List<Map<String, Object>> books =
reader.read(“$.store.book[?].isbn”, List.class, booksWithISBN);
Path vs Value
In the Goessner implementation a JsonPath can return
either Path or Value. Value is the default and what all the examples
above are returning. If you rather have the path of the elements our
query is hitting this can be achieved with an option.
Configuration conf = Configuration.builder()
.options(Option.AS_PATH_LIST).build();
List
assertThat(pathList).containsExactly(
“$[‘store’][‘book’][0][‘author’]”,
“$[‘store’][‘book’][1][‘author’]”,
“$[‘store’][‘book’][2][‘author’]”,
“$[‘store’][‘book’][3][‘author’]”);
Set a value
The library offers the possibility to set a value.
String newJson =
JsonPath.parse(json).set(“$[‘store’][‘book’][0][‘author’]”,
“Paul”).jsonString();
Tweaking Configuration
Options
When creating your Configuration there are a few option flags that can
alter the default behaviour.
DEFAULT_PATH_LEAF_TO_NULL
This option makes JsonPath return null for missing leafs. Consider the
following json
[
{
“name” : “john”,
“gender” : “male”
},
{
“name” : “ben”
}
]
Configuration conf = Configuration.defaultConfiguration();
//Works fine
String gender0 =
JsonPath.using(conf).parse(json).read(“$[0][‘gender’]”);
//PathNotFoundException thrown
String gender1 =
JsonPath.using(conf).parse(json).read(“$[1][‘gender’]”);
Configuration conf2 = conf.addOptions(Option.DEFAULT_PATH_LEAF_TO_NULL);
//Works fine
String gender0 =
JsonPath.using(conf2).parse(json).read(“$[0][‘gender’]”);
//Works fine (null is returned)
String gender1 =
JsonPath.using(conf2).parse(json).read(“$[1][‘gender’]”);
ALWAYS_RETURN_LIST
This option configures JsonPath to return a list even when the path
is definite.
Configuration conf = Configuration.defaultConfiguration();
//ClassCastException thrown
List
JsonPath.using(conf).parse(json).read(“$[0][‘gender’]”);
Configuration conf2 = conf.addOptions(Option.ALWAYS_RETURN_LIST);
//Works fine
List
JsonPath.using(conf2).parse(json).read(“$[0][‘gender’]”);
SUPPRESS_EXCEPTIONS
This option makes sure no exceptions are propagated from path
evaluation. It follows these simple rules:
If option ALWAYS_RETURN_LIST is present an empty list will be
returnedIf option ALWAYS_RETURN_LIST is NOT present null returned
REQUIRE_PROPERTIES
This option configures JsonPath to require properties defined in path
when an indefinite path is evaluated.
Configuration conf = Configuration.defaultConfiguration();
//Works fine
List
JsonPath.using(conf).parse(json).read(“$[*][‘gender’]”);
Configuration conf2 = conf.addOptions(Option.REQUIRE_PROPERTIES);
//PathNotFoundException thrown
List
JsonPath.using(conf2).parse(json).read(“$[*][‘gender’]”);
JsonProvider SPI
JsonPath is shipped with five different JsonProviders:
[JsonSmartJsonProvider]{.ul} (default)
Changing the configuration defaults as demonstrated should only be done
when your application is being initialized. Changes during runtime is
strongly discouraged, especially in multi threaded applications.
Configuration.setDefaults(new Configuration.Defaults() {
private final JsonProvider jsonProvider = new JacksonJsonProvider();
private final MappingProvider mappingProvider = new
JacksonMappingProvider();
@Override
public JsonProvider jsonProvider() {
return jsonProvider;
}
@Override
public MappingProvider mappingProvider() {
return mappingProvider;
}
@Override
public Set
return EnumSet.noneOf(Option.class);
}
});
Note that the JacksonJsonProvider
requires com.fasterxml.jackson.core:jackson-databind:2.4.5 and the
GsonJsonProvider requires com.google.code.gson:gson:2.3.1 on your
classpath.
Cache SPI
In JsonPath 2.1.0 a new Cache SPI was introduced. This allows API
consumers to configure path caching in a way that suits their needs. The
cache must be configured before it is accesses for the first time or a
JsonPathException is thrown. JsonPath ships with two cache
implementations
com.jayway.jsonpath.spi.cache.LRUCache (default, thread safe)
com.jayway.jsonpath.spi.cache.NOOPCache (no cache)
If you want to implement your own cache the API is simple.
CacheProvider.setCache(new Cache() {
//Not thread safe simple cache
private Map<String, JsonPath> map = new HashMap<String, JsonPath>();
@Override
public JsonPath get(String key) {
return map.get(key);
}
@Override
public void put(String key, JsonPath jsonPath) {
map.put(key, jsonPath);
}
});
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