SimpleJSON Library (JSON Parsing Library)
What Is JSON?
JSON (JavaScript Object Notation) is a lightweight text-based data format (notation)
It is used to exchange data between various languages such as JavaScript and Python
Overview
The SimpleJSON library is a JSON parsing library created for OMRON NX/NJ series PLCs.
It converts JSON data received via MQTT or REST API communication into Dictionary form so Values can easily be obtained by specifying Keys.
It can be used for integration with AWS IoT Core and various cloud services.
When JSON Is Used on PLCs
JSON is the most commonly used data format in MQTT and REST API communication.
It is used for data integration with AWS IoT Core, Azure IoT Hub, Node-RED, Python applications and more.
Basic JSON example
| Strings | Characters (UTF-8) enclosed in " (double quotes) |
| Numbers | Integer, negative and decimal values and exponential notation (hexadecimal notation and leading zeros are not allowed) |
| Boolean | true、false |
| Object | Characters enclosed in {} |
| Array | Characters enclosed in [] |
Specifications of This SimpleJSON Library
| Bytes of JSON that can be handled | 65535 |
| Number of Keys | 100 |
| Bytes per Key | 50 bytes (including all nested objects *1) |
| Bytes per Value | 1986 byte |
When the Value is an object, it is nested
Everything other than objects is stored as a string
| String | Stored including " (double quotes) |
| Value | Stored as a string |
| Arrays | Everything from "[" to "]" is stored as a string |
Nested objects
When there is an object inside an object, Keys are joined with . (dot)
Conversion examples
Keys and Values when JSON is converted to a Dictionary
JSON
| Key | Value |
|---|---|
| name | "taro" |
| age | 29 |
| image.visible | true |
| image.Title | "View from 15th Floor" |
| image.Thumbnail.Url | "http://www.example.com" |
| image.Thumbnail.Height | 125 |
| image.Thumbnail.Width | 100 |
| image.IDs | [116,943, 234, 38793] |
Functions included in the library
The namespace is "SimpleJSON"
- Deserialize: converts JSON to a Dictionary
- GetAryData: extracts elements from a JSON array
- CharSearch: searches a byte array for a character
- Get: gets a Value by specifying a Dictionary Key
Example
Usage is explained in the SimpleJSON library usage example
FAQ
Does it support arrays?
Yes. The entire array is held as a string.
Does it support nested objects?
Yes. Keys are managed dot-separated.
Can it be used with AWS MQTT?
Yes. It is suited to parsing JSON data received via MQTT.
Library features
- Convert JSON to a Dictionary
- Supports nested objects
- Get Values by Key
- Supports Sysmac Studio
- Can be used to parse MQTT communication data
- Free of charge
