JSONレスポンスを解析する

A server reply arrives as one long string. To use a value inside it, you first have to pull that value out cleanly.

Hunting through text with indexOf is fragile. A real JSON parser understands the structure and gives you fields safely.

The ArduinoJson library turns a JSON string into objects you can read by key. Install it from the Library Manager.

Create a JsonDocument to hold the parsed data. It is the container ArduinoJson fills in for you.

Call deserializeJson() with your document and the response text. This reads the string and fills the document.

deserializeJson returns an error you should test. Bad or partial JSON should be caught before you trust any field.

Access a value with its key, just like a dictionary. Tell ArduinoJson the type you expect for that field.

For nested JSON, chain the keys. Each bracket steps one level deeper into the structure to reach the value you want.

If a field is a JSON array, you can walk it with a for loop and read each element in turn.

A JsonDocument uses memory. Keep it just big enough for your data, since RAM on a microcontroller is limited.

Treat a parsed string as valid only while the source text still exists. Copy it out if you need it to last longer.

Which function actually converts the JSON text into a readable document?

You used ArduinoJson to deserialize a response, checked for errors, and read fields and arrays by key. Raw text is now real data. 🎉