3 minutes to understand JSON schema

Hello everyone , I'm not fish skin .

Lucky and unfortunate , I am a programmer , He's also a programmer .

Over the weekend , I'm developing a website , He's developing games , Two people write code together , Write together Bug bald , There was a different kind of romance , Not at ease ！

Pair programming

today , He met a backstage Bug, The game won't start , Let me help you check , By the way, let's share some programming knowledge ~

Bug cause

At the beginning of the game , First, load some configurations , For example, the user name of the player 、 The difficulty of the level 、 Player's initial props, etc .

Because the game is using Java Language development , He encapsulates these configurations into an object , The code is as follows ：

//  Game configuration 
class GameConfig {
  //  Player name 
  String name;
  //  The difficulty of the game 
  int difficulty;
  //  Player items 
  String[] items;
}

For the convenience of development and debugging , He wrote a default configuration ; And for the convenience of managing the default configuration , Put it in a separate JSON Format file , Not in code .

Default JSON The configuration file is as follows ：

{
  "name": "yupi",
  "difficulty": 5,
  "items": [" Primary head ", " Secondary a "]
}

And then in the program , Read the... In the configuration file JSON character string , Re pass Gson The parsing library will JSON String conversion to Java object , You can get the game configuration information , So as to proceed to the next step .

The logic code is as follows ：

//  Load game configuration 
void loadConfig() {
  String jsonStr = loadFile('config.json');
  GameConfig config = new Gson()
    .fromJson(jsonStr, GameConfig.class);
  //  Get player name 
  String name = config.getName();
	//  More processing 
  ...
}

The whole process looks very simple , Why do you report mistakes ？

Print out the abnormal information , Obviously , yes JSON Parsing error ：

Take a closer look. , Ah , This little fool , The configuration file was entered incorrectly , A necessary quote is missing at the end of the line , Of course, the parsing failed ！

{
  //  A quote is missing at the end of the line 
  "items": [" Primary head ", " Secondary a ]
}

He said he was helpless , Can't , During development, the configuration heap is more and more 、 Change from one place to another , If you don't pay attention, you'll type less characters .

I laugh so much ：JSON The format is really flexible and powerful , We are at work , Also often write some complex nested JSON. I know a way , It can help reduce JSON The probability that the file is written incorrectly .

He didn't think so ： Oh , What's the solution ？ Check with the editor or check the website ？

I ： Then you can only check the basic grammar , Come on, come on , Give you a better artifact —— JSON Schema！

JSON Schema

JSON One of the advantages of the format is its lightweight , It itself does not support writing comments , Therefore, there is no way to describe the fields directly in the file itself .

therefore , If we use JSON To make the configuration file , In most cases, you have to look at the document to see the type of each field 、 Limits , To write the correct configuration . This is not only inefficient , And you must verify whether the configuration written is correct , I accidentally made a mistake .

and JSON Schema Is born to solve this problem , He himself is JSON file , Used to annotate and verify JSON file .

for instance , In the game configuration above , Because you accidentally input the wrong string array, the program went wrong Bug. Then you can write a JSON Schema To verify items Whether the field is a legal array , The code is as follows ：

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://www.code-nav.cn/latest.json",
  "title": "GameConfig",
  "description": " Game configuration ",
  "type": "object",
  "properties": {
    "items": {
      "type": "array"
    }
  }
}

In this file , It specifies GameConfig The type of must be object（ object ）, And items Property type must be array（ Array ）.

Next, specify... In the data to be verified "$schema" The field is the address of the verification file , Like the following JSON To configure , Deliberately put items The value of the field is set to string（ character string ） Not an array ：

{
  "$schema": "https://www.code-nav.cn/latest.json",
  {
  	"name": "yupi",
  	"difficulty": 5,
  	"items": "haha"
	}
}

In this way, we can check whether the data is legal ！ Many mainstream editors （ such as JetBrains Family bucket ） It can automatically identify the verification file , And check your JSON Whether the input is legal . You can also use JSON Schema validation online Wait for online verification JSON Schema To see the effect ：

Online verification

JSON Schema Very powerful , In addition to the verification of field types , It also supports judging whether fields are required 、 Whether it is a value （ regular expression ）、 Max min 、 Number of fields 、 Enumeration, etc , It even supports the combination of multiple judgment conditions ！

For example, you can also add verification to the difficulty field of our game configuration , Must be 1 To 5 Number between , The grammar is as follows ：

"difficulty": {
  "type": "number",
  "minimum": 1,
  "maximum": 5
}

advantage

Understand what is JSON Schema after , Summarize its advantages ：

1. Describe the data format , Improve readability , Help humans understand
2. Let the machine understand the data better , So as to provide functions such as data verification and prompt input
3. Provides a unified data specification Syntax , It is convenient to realize interface format verification 、 automated testing , You can even use it to automatically generate code ！ such as jsonschema2pojo Tools , according to JSON Generate Java class .

Automatic code generation

All in all , Make good use of JSON Schema, It can greatly reduce the communication cost of developers 、 Just ensure the quality of the code . After all JSON But the most popular data exchange format in front and back-end development today ！

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