JsonPath仓库

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JSONPath

A Java DSL for reading JSON documents.

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.
`.<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.

Path Examples

Given the

{
    "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	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[(@.length-1)]`	The 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
`$..book[2:]`	Book number two from tail
`$..book[?(@.isbn)]`	All books with an ISBN number
`$.store.book[?(@.price < 10)]`	All books in store cheaper than 10
`$..book[?(@.price <= $['expensive'])]`	All books in store that are not "expensive"
`$..*`	Give me every thing you got

Reading a document

The simplest most straight forward way to use JsonPath is via the static convenience API.

String json = "...";

List<String> authors = JsonPath.read(json, "$.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 author1 = JsonPath.read(document, "$.store.book[0].author");
String author2 = JsonPath.read(document, "$.store.book[1].author");

Personally I prefer the more flexible ReadContext API.

String json = "...";

ReadContext ctx = JsonPath.parse(json);

List<String> authorsOfBooksWithISBN = 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. Json path will automatically try to cast the result to the type expected by the invoker.

//Will throw an java.lang.ClassCastException    
List<String>  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 not definite if it contains:

.. - a deep scan operator
?(<expression>) - an expression
[<number>, <number> (, <number>)] - multiple array indexes
['<name>', '<name>' (, '<name>')] - multiple object properties

Non definite paths always returns a list.

By default some simple conversions are provided by the MappingProvider. This allows to specify the return type you want and the MappingProvider will try to perform the mapping. If a book, in the sample json above, had a long value 'published' you could perform object mapping between Long and Date as shown below.

Date date = JsonPath.parse(json).read("$.store.book[0].published", date.class)

If you use the JacksonJsonProvider you can even map your JsonPath output directly into POJO's.

Book book = JsonPath.parse(json).read("$.store.book[0]", Book.class)

Predicates

There are three different ways to create filter predicates in JsonPath.

###Inline predicates

These are predicates baked right into to your path.

List<Map<String, Object>> books =  JsonPath.parse(json).read("$.store.book[?(@.price < 10)]");

In the current implementation you can use && to combine multiple predicates [?(@.price < 10 && @.category == 'fiction')]. OR operations are not supported yet.

###The Filter API

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 = where(where("category").is("fiction").and("price").lte(10D));

List<Map<String, Object>> books =  parse(json).read("$.store.book[?]", cheapFictionFilter);

Note 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.

###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

Tweaking Configuration

The default JsonProvider is JsonSmartJsonProvider backed by json-smart, a small and fast JSONParser. If you prefer Jackson there is a JacksonJsonProvider available. There is also an experimental GsonJsonProvider.

JacksonJsonProvider requires com.fasterxml.jackson.core:jackson-databind:2.4.1.3 on your classpath.
GsonJsonProvider requires com.google.code.gson:gson:2.3 on your classpath.

Configuration.setDefaults(new Configuration.Defaults() {

    private final JsonProvider jsonProvider = new com.jayway.jsonpath.internal.spi.json.JacksonJsonProvider();
      
    @Override
    public JsonProvider jsonProvider() {
        return jsonProvider;
    }

    @Override
    public Set<Option> options() {
        return EnumSet.noneOf(Option.class);
    }

    @Override
    public MappingProvider mappingProvider() {
        return new DefaultMappingProvider();
    }
});

Binaries

JsonPath is available at the Central Maven Repository. Maven users add this to your POM.

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>0.9.1</version>
</dependency>

Gradle users

compile 'com.jayway.jsonpath:json-path:0.9.1'

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