使用 JSONPath 解析 JSON内容详细

JSONPath的介绍：

JsonPath 是一种简单的方法来提取给定JSON文档的部分内容。
JsonPath表达式总是以与XPath表达式结合使用XML文档相同的方式引用JSON结构。
JsonPath中的“根成员对象”始终称为$，无论是对象还是数组。

JsonPath 对应的maven包

<dependency><groupId>com.jayway.jsonpath</groupId><artifactId>json-path</artifactId><version>2.2.0</version>
</dependency>

操作符：说明JSONPath语法元素和对应XPath元素的对比

函数

函数可以在路径的尾部调用，函数的输出是路径表达式的输出，该函数的输出是由函数本身所决定的。

函数	描述	输出
min()	提供数字数组的最小值	Double
max()	提供数字数组的最大值	Double
avg()	提供数字数组的平均值	Double
stddev()	提供数字数组的标准偏差值	Double
length()	提供数组的长度	Integer

过滤器运算符

过滤器是用于筛选数组的逻辑表达式。一个典型的过滤器将是[?(@.age > 18)]，其中@表示正在处理的当前项目。可以使用逻辑运算符&&和||创建更复杂的过滤器。字符串文字必须用单引号或双引号括起来([?(@.color == ‘blue’)] 或者 [?(@.color == “blue”)]).

操作符	描述
==	left等于right（注意1不等于’1’）
!=	不等于
<	小于
<=	小于等于
>	大于
>=	大于等于
=~	匹配正则表达式[?(@.name =~ /foo.*?/i)]
in	左边存在于右边 [?(@.size in [‘S’, ‘M’])]
nin	左边不存在于右边
size	（数组或字符串）长度
empty	（数组或字符串）为空

Java操作实例

{"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
}

编号	JsonPath	结果
1	$.store.book[*].author	获取json中store下book下的所有author值
2	$…author	获取所有json中所有author的值
3	$.store.*	所有的东西，书籍和自行车
4	$.store…price	获取json中store下所有price的值
5	$…book[2]	获取json中book数组的第3个值
6	$…book[-2]	倒数的第二本书
7	$…book[0,1]	前两本书
8	$…book[:2]	从索引0（包括）到索引2（排除）的所有图书
9	$…book[1:2]	从索引1（包括）到索引2（排除）的所有图书
10	$…book[-2:]	获取json中book数组的最后两个值
11	$…book[2:]	获取json中book数组的第3个到最后一个的区间值
12	$…book[?(@.isbn)]	获取json中book数组中包含isbn的所有值
13	$.store.book[?(@.price < 10)]	获取json中book数组中price<10的所有值
14	$…book[?(@.price <= $[‘expensive’])]	获取json中book数组中price<=expensive的所有值
15	$…book[?(@.author =~ /.*REES/i)]	获取json中book数组中的作者以REES结尾的所有值（REES不区分大小写）
16	$…*	逐层列出json中的所有值，层级由外到内
17	$…book.length()	获取json中book数组的长度

以上的三个点都是两个点

结果：

编号1：

["Nigel Rees","Evelyn Waugh","Herman Melville","J. R. R. Tolkien"
]

编号2：

["Nigel Rees","Evelyn Waugh","Herman Melville","J. R. R. Tolkien"
]

编号3：

[[{"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}],{"color" : "red","price" : 19.95}
]

编号4：

[8.95,12.99,8.99,22.99,19.95
]

编号5：

[{"category" : "fiction","author" : "Herman Melville","title" : "Moby Dick","isbn" : "0-553-21311-3","price" : 8.99}
]

编号6：

[{"category" : "fiction","author" : "Herman Melville","title" : "Moby Dick","isbn" : "0-553-21311-3","price" : 8.99}
]

编号7：

[{"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}
]

编号8：

[{"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}
]

编号9：

[{"category" : "fiction","author" : "Evelyn Waugh","title" : "Sword of Honour","price" : 12.99}
]

编号10：

[{"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}
]

编号11：

[{"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}
]

编号12：

[{"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}
]

编号13：

[{"category" : "reference","author" : "Nigel Rees","title" : "Sayings of the Century","price" : 8.95},{"category" : "fiction","author" : "Herman Melville","title" : "Moby Dick","isbn" : "0-553-21311-3","price" : 8.99}
]

编号14：

[{"category" : "reference","author" : "Nigel Rees","title" : "Sayings of the Century","price" : 8.95},{"category" : "fiction","author" : "Herman Melville","title" : "Moby Dick","isbn" : "0-553-21311-3","price" : 8.99}
]

编号15：

[{"category" : "reference","author" : "Nigel Rees","title" : "Sayings of the Century","price" : 8.95}
]

编号16：

[{"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}},10,[{"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}],{"color" : "red","price" : 19.95},{"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},"reference","Nigel Rees","Sayings of the Century",8.95,"fiction","Evelyn Waugh","Sword of Honour",12.99,"fiction","Herman Melville","Moby Dick","0-553-21311-3",8.99,"fiction","J. R. R. Tolkien","The Lord of the Rings","0-395-19395-8",22.99,"red",19.95
]

编号17：

json字符串的读取

方法一：解析一次json

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

方法二：对同一个json解析多次，可以使用ReadContext、WriteContext

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);

返回类型

1.通常read后的返回值会进行自动转型到指定的类型，对应明确定义definite的表达式，应指定其对应的类型。

// 抛出 java.lang.ClassCastException 异常
List<String> list = JsonPath.parse(json).read("$.store.book[0].author")// 正常
String author = JsonPath.parse(json).read("$.store.book[0].author")

2.默认情况下，MappingProvider SPI提供了一个简单的对象映射器。这允许您指定所需的返回类型，MappingProvider将尝试执行映射。在下面的示例中，演示了Long和Date之间的映射。

String json = "{\"date_as_long\" : 1411455611975}";
Date date = JsonPath.parse(json).read("$['date_as_long']", Date.class);

3.如果您将JsonPath配置为使用JacksonMappingProvider或GsonMappingProvider，您甚至可以将JsonPath输出直接映射到POJO中。

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

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