当我们需要提取Json中的数据到变量时，需要用到JsonPath表达式，JsonPath和XPath有点相似，但写法却是不一样的，这里我们对比一下XPath来学习JsonPath的用法。 先上一段Json字符：
{ "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
}
}
}
比如我们要提取第一本书(book)的标题(title)，如果我们把它当做是Xml的话，可以这样写
XPath：/store/book[1]/title
而使用JsonPath则是这样写
JsonPath：$.store.book[0].title
或者也可以这样写 $['store']['book'][0]['title']
JsonPath中的$相当于Xpath中的首字符"/"，代表“根成员对象”，因为JSON结构通常是匿名的，不一定有一个“根成员对象”，所以这个$实际上是虚拟出来的，这里我们不用管它，知道他代表根对象就行了。而XPath中间部分的子操作符“/“，在JsonPath中则是用"."来表示，或者用第二种写法，用中括号"[]"来括住节点名称(节点名称要加上单引号)。
下面列个表格对比一下
XPath | JsonPath | 说明 |
/ | $ | 根对象/元素 |
. | @ | 当前对象/元素 |
/ | . or [] | 子操作符 |
.. | n/a | 父操作符 |
// | .. | 递归查找所有级别的子级元素 |
* | * | 通配符 |
@ | 无 | 查找指定属性，json中无属性的定义 |
[] | [] | 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. |
无 | [start:end:step] | array slice operator borrowed from ES4. |
[] | ?() | 用于过滤 |
无 | () | 脚本表达式,使用底层的脚本引擎。 |
() | 无 | Xpath中的分组 |
再看几个表达式的对比
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. |
以上资料整理参考网址
http://goessner.net/articles/JsonPath/
