JSON Schema详解

熟悉XML的开发人员都知道，对XML文档的定义有一个XML Schema。

同样，对于JSON文件的定义，也应该有一个JSON Schema以规范JSON文件内容。

JSON Schema用以标注和验证JSON文档的元数据的文档，可以类比于XML Schema。相对于JSON Schema，一个JSON文档就是JSON Schema的一个instance。

1.JSON Schema规范

IETF负责起草相关规范
最新版本是2017-4-15发布的Draft 6
http://json-schema.org/draft-06/schema
2. JSON Schema规范组成

• JSON Schema Core
• JSON Schema Validation
• JSON Hyper-Schema

3. 规范概览
1)Type-specific keywords

			{ "type": "string", 
			  "pattern": "^(\\([0-9]{3}\\))?[0-9]{3}-[0-9]{4}$", 
			  "minLength": 2, 
			  "maxLength": 3, 
			  "format": "date-time|email|hostname|ipv4|ipv6|uri" }

			{ "type": "number",
			  "minimum": 0,
			  "maximum": 100 }

			{ "type": "integer" }

			{ "type": "object",
			  "properties": {
			    "name": { "type": "string" },
			    "credit_card": { "type": "number" }
			  },
			  "required": ["name"] }

			{ "type": "array",
			  "minItems": 2,
			  "maxItems": 3, 
			  "items": {
			    "type": "number"
			  } }

			{ "type": "boolean" }

			{ "type": "null" }

组合

			{ "type": ["number", "string"] }

2)Generic keywords

			{
			  "title" : "Match anything",
			  "description" : "This is a schema that matches anything.",
			  "default" : "Default value"
			}

3)Combining schemas

• not

			{ "not": { "type": "string" } }

• allOf

			{
			  "allOf": [
			    { "type": "string" },
			    { "maxLength": 5 }
			  ]
			}

• anyOf

			{
			  "anyOf": [
			    { "type": "string", "maxLength": 5 },
			    { "type": "number", "minimum": 0 }
			  ]
			}

• oneOf

			{
			  "oneOf": [
			    { "type": "number", "multipleOf": 5 },
			    { "type": "number", "multipleOf": 3 }
			  ]
			}

4)$schema keyword
"$schema": "http://json-schema.org/schema#"
"$schema": "http://json-schema.org/draft-06/schema#"
5)Regular Expressions
6) $ref keyword

• 基本复用

{ "$ref": "#/currentdoc/definitions/address" }

或
{ "$ref": "asidedoc_definitions.json#/address" }

• id设置基本URI

"id": "http://foo.bar/schemas/address.json"
{ "$ref": "person.json" }

• 扩展复用

			"shipping_address": {
			  "allOf": [
			    // Here, we include our "core" address schema...
			    { "$ref": "#/definitions/address" },
			
			    // ...and then extend it with stuff specific to a shipping
			    // address
			    { "properties": {
			        "type": { "enum": [ "residential", "business" ] }
			      },
			      "required": ["type"]
			    }
			  ]
			}

4. 解析软件

• Java

https://github.com/everit-org/json-schema
https://github.com/java-json-tools/json-schema-validator
https://github.com/networknt/json-schema-validator

• Python

https://github.com/Julian/jsonschema
https://github.com/zyga/json-schema-validator

• Online

http://jsonschemalint.com/

参考链接：

http://json-schema.org/