JsonPath详解

 

JsonPath is to JSON what XPATH is to XML, a simple way to extract parts of a given document. JsonPath is available in many programming languages such as Javascript, Python and PHP. Now also in Java!
News
 
2013-09-27 Released 0.9.0 bug fixes, general improvements
 
2012-04-16 Released 0.8.1 bug fixes, improved docs, general improvements
 
2012-03-08 Released 0.8.0 bug fixes, Filter builder, Json model, POJO mapping (optional) and compliance improvements.
 
2012-02-09 Released 0.5.6 including bug fixes and performance improvements.
Given
 
{ "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,
        "isbn": "0-553-21311-3"
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}
 
Read
 
All authors:
 
List<String> authors = JsonPath.read(json, "$.store.book[*].author");
 
Author of first book in store:
 
String author = JsonPath.read(json, "$.store.book[1].author");
 
All books with category = "reference"
 
List<Object> books = JsonPath.read(json, "$.store.book[?(@.category == 'reference')]");
 
List<Object> books = JsonPath.read(json, "$.store.book[?]", filter(where("category").is("reference")));
 
All books that cost more than 10 USD
 
List<Object> books = JsonPath.read(json, "$.store.book[?(@.price > 10)]");
 
List<Object> books = JsonPath.read(json, "$.store.book[?]", filter(where("price").gt(10)));
 
All books that have isbn
 
List<Object> books = JsonPath.read(json, "$.store.book[?(@.isbn)]");
 
List<Object> books = JsonPath.read(json, "$.store.book[?]", filter(where("isbn").exists(true)));
 
Chained filters
 
Filter filter = Filter.filter(Criteria.where("isbn").exists(true).and("category").in("fiction", "reference"))
 
List<Object> books = JsonPath.read(json, "$.store.book[?]", filter);
 
Custom filters
 
Filter myFilter = new Filter.FilterAdapter<Map<String, Object>>(){
                @Override
                public boolean accept(Map<String, Object> map) {
                     return map.containsKey("isbn");  
                }
            };
 
List<Object> books = JsonPath.read(json, "$.store.book[?]", myFilter);
 
All prices in the document
 
List<Double> prices = JsonPath.read(json, "$..price");
 
Compiled path
 
You can pre compile a path and use it multiple times
 
JsonPath path = JsonPath.compile("$.store.book[*]");
 
List<Object> books = path.read(json);
 
Assert
 
Asserts are made with Hamcrest matchers
 
JsonAssert.with(json).assertThat("$.store.bicycle.color", Matchers.equalTo("red"))
          .assertThat("$.store.bicycle.price", Matchers.equalTo(19.95D));
 
Add some static imports and you get this
 
with(json).assertThat("$.store.bicycle.color", equalTo("red"))
          .assertThat("$.store.bicycle.price", equalTo(19.95D));
 
The Hamcrest library contains a lot of different matchers and they can often be nested.
 
with(json).assertThat("$..author", hasItems("Nigel Rees", "Evelyn Waugh"))
          .assertThat("$..author", is(collectionWithSize(equalTo(2))));
 
with(json).assertThat("$.store.book[?(@.category == 'x')]", emptyCollection());
 
If you don't find the matcher you need, roll your own.
Download
 
Json-path is available at Maven Central
 
<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>0.9.1</version>
</dependency>
 
<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path-assert</artifactId>
    <version>0.9.1</version>
    <scope>test</scope>
</dependency>

 

 

 

# JSONPath - XPath for JSON

A frequently emphasized advantage of XML is the availability of plenty tools to analyse, transform and selectively extract data out of XML documents. XPath is one of these powerful tools.

It's time to wonder, if there is a need for something like XPath4JSON and what are the problems it can solve.

  • Data may be interactively found and extracted out of JSON structures on the client without special scripting.
  • JSON data requested by the client can be reduced to the relevant parts on the server, such minimizing the bandwidth usage of the server response.

If we agree, that a tool for picking parts out of a JSON structure at hand does make sense, some questions come up. How should it do its job? How do JSONPath expressions look like?

Due to the fact, that JSON is a natural representation of data for the C family of programming languages, the chances are high, that the particular language has native syntax elements to access a JSON structure.

The following XPath expression

/store/book[1]/title

would look like

x.store.book[0].title

or

x['store']['book'][0]['title']

in Javascript, Python and PHP with a variable x holding the JSON structure. Here we observe, that the particular language usually has a fundamental XPath feature already built in.

The JSONPath tool in question should …

  • be naturally based on those language characteristics.
  • cover only essential parts of XPath 1.0.
  • be lightweight in code size and memory consumption.
  • be runtime efficient.

|2007-08-17| e2# JSONPath expressions

JSONPath expressions always refer to a JSON structure in the same way as XPath expression are used in combination with an XML document. Since a JSON structure is usually anonymous and doesn't necessarily have a "root member object" JSONPath assumes the abstract name $ assigned to the outer level object.

JSONPath expressions can use the dot–notation

$.store.book[0].title

or the bracket–notation

$['store']['book'][0]['title']

for input pathes. Internal or output pathes will always be converted to the more general bracket–notation.

JSONPath allows the wildcard symbol * for member names and array indices. It borrows thedescendant operator '..' from E4X and the array slice syntax proposal [start:end:step] fromECMASCRIPT 4.

Expressions of the underlying scripting language (<expr>) can be used as an alternative to explicit names or indices as in

$.store.book[(@.length-1)].title

using the symbol '@' for the current object. Filter expressions are supported via the syntax ?(<boolean expr>) as in

$.store.book[?(@.price < 10)].title

Here is a complete overview and a side by side comparison of the JSONPath syntax elements with its XPath counterparts.

XPath JSONPath Description
/ $ the root object/element
. @ the current object/element
/ . or [] child operator
.. n/a parent operator
// .. recursive descent. JSONPath borrows this syntax from E4X.
* * wildcard. All objects/elements regardless their names.
@ n/a attribute access. JSON structures don't have attributes.
[] [] subscript operator. XPath uses it to iterate over element collections and for predicates. In Javascript and JSON it is the native array operator.
| [,] Union operator in XPath results in a combination of node sets. JSONPath allows alternate names or array indices as a set.
n/a [start:end:step] array slice operator borrowed from ES4.
[] ?() applies a filter (script) expression.
n/a () script expression, using the underlying script engine.
() n/a grouping in Xpath

XPath has a lot more to offer (Location pathes in not abbreviated syntax, operators and functions) than listed here. Moreover there is a remarkable difference how the subscript operator works in Xpath and JSONPath.

  • Square brackets in XPath expressions always operate on the node set resulting from the previous path fragment. Indices always start by 1.
  • With JSONPath square brackets operate on the object or array addressed by the previous path fragment. Indices always start by 0.

|2007-08-18| e3# JSONPath examples

Let's practice JSONPath expressions by some more examples. We start with a simple JSON structure built after an XML example representing a bookstore (original XML file).

{ "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
    }
  }
}
XPath JSONPath Result
/store/book/author $.store.book[*].author the authors of all books in the store
//author $..author all authors
/store/* $.store.* all things in store, which are some books and a red bicycle.
/store//price $.store..price the price of everything in the store.
//book[3] $..book[2] the third book
//book[last()] $..book[(@.length-1)]
$..book[-1:]		 the last book in order.
//book[position()<3] $..book[0,1]
$..book[:2]		 the first two books
//book[isbn] $..book[?(@.isbn)] filter all books with isbn number
//book[price<10] $..book[?(@.price<10)] filter all books cheapier than 10
//* $..* all Elements in XML document. All members of JSON structure.

|2007-08-22| e4# JSONPath implementation

JSONPath is implemented in Javascript for clientside usage and ported over to PHP for use on the server.

Usage

All you need to do is downloading either of the files

include it in your program and use the simple API consisting of one single function.

jsonPath(obj, expr [, args])

parameters:

obj (object|array):
Object representing the JSON structure.
expr (string):
JSONPath expression string.
args (object|undefined):
Object controlling path evaluation and output. Currently only one member is supported.
args.resultType ("VALUE"|"PATH"):
causes the result to be either matching values (default) or normalized path expressions.

return value:

(array|false):
Array holding either values or normalized path expressions matching the input path expression, which can be used for lazy evaluation. false in case of no match.

Javascript Example:

var o = { /*...*/ },  // the 'store' JSON object from above
    res1 = jsonPath(o, "$..author").toJSONString(),
    res2 = jsonPath(o, "$..author", {resultType:"PATH"}).toJSONString();

PHP example:

We need here to convert the JSON string to a PHP array first. I am using Michal Migurski's JSON parser for that.

require_once('json.php');      // JSON parser
require_once('jsonpath.php');  // JSONPath evaluator

$json = '{ ... }';  // JSON structure from above

$parser = new Services_JSON(SERVICES_JSON_LOOSE_TYPE);
$o = $parser->decode($json);
$match1 = jsonPath($o, "$..author");
$match2 = jsonPath($o, "$..author", array("resultType" => "PATH"));
$res1 = $parser->encode($match1);
$res2 = $parser->encode($match2);

results

Both Javascript and PHP example result in the following JSON arrays (as strings):

res1:
[ "Nigel Rees",
  "Evelyn Waugh",
  "Herman Melville",
  "J. R. R. Tolkien"
]
res2:
[ "$['store']['book'][0]['author']",
  "$['store']['book'][1]['author']",
  "$['store']['book'][2]['author']",
  "$['store']['book'][3]['author']"
]

Please note, that the return value of jsonPath is an array, which is also a valid JSON structure. So you might want to apply jsonPath to the resulting structure again or use one of your favorite array methods as sort with it.

|2007-08-24| e5# Issues

  • Currently only single quotes allowed inside of JSONPath expressions.
  • Script expressions inside of JSONPath locations are currently not recursively evaluated byjsonPath. Only the global $ and local @ symbols are expanded by a simple regular expression.
  • An alternative for jsonPath to return false in case of no match may be to return an empty array in future.

 

 

 

JSON 信息抽取类库：JsonPath

JsonPath 对于 JSON 来说相当于 XPATH 对于 XML。这是一个简单的从文档中抽取指定信息的工具，提供多种语言实现版本，包括：Javascript, Java, Python 和 PHP。


给定以下JSON字符串：
{ "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,
        "isbn": "0-553-21311-3"
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

读取

所有作者:

List<String> authors = JsonPath.read(json, "$.store.book[*].author");

Author of first book in store:

String author = JsonPath.read(json, "$.store.book[1].author");

所有分类="reference"的书籍

List<Object> books = JsonPath.read(json, "$.store.book[?(@.category == 'reference')]");

List<Object> books = JsonPath.read(json, "$.store.book[?]", filter(where("category").is("reference")));





参考：
http://goessner.net/articles/JsonPath/
http://www.oschina.net/code/snippet_273576_34427
https://github.com/jayway/JsonPath
http://mvnrepository.com/artifact/com.jayway.jsonpath/json-path/2.2.0
http://www.oschina.net/p/jsonpath
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原文地址：https://www.cnblogs.com/timssd/p/5797249.html