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get a json value quickly

GJSON is a Go package the provides a very fast and simple way to get a value from a json document. The reason for this library it to give efficent json indexing for the BuntDB project.

Getting Started

Installing

To start using GJSON, install Go and run go get:

$ go get -u github.com/tidwall/gjson

This will retrieve the library.

Get a value

Get searches json for the specified path. A path is in dot syntax, such as "name.last" or "age". This function expects that the json is well-formed, and does not validate. Invalid json will not panic, but it may return back unexpected results. When the value is found it's returned immediately.

package main

import "github.com/tidwall/gjson"

const json = `{"name":{"first":"Janet","last":"Prichard"},"age":47}`

func main() {
	value := gjson.Get(json, "name.last")
	println(value.String())
}

This will print:

Prichard

A path is a series of keys seperated by a dot. A key may contain special wildcard characters '*' and '?'. To access an array value use the index as the key. To get the number of elements in an array use the '#' character.

{
  "name": {"first": "Tom", "last": "Anderson"},
  "age":37,
  "children": ["Sara","Alex","Jack"]
}
"name.last"          >> "Anderson"
"age"                >> 37
"children.#"         >> 3
"children.1"         >> "Alex"
"child*.2"           >> "Jack"
"c?ildren.0"         >> "Sara"

Result Type

GJSON supports the json types string, number, bool, and null. Arrays and Objects are returned as their raw json types.

The Result type holds one of these types:

bool, for JSON booleans
float64, for JSON numbers
Number, for JSON numbers
string, for JSON string literals
nil, for JSON null

To get the value call the Value() method:

result.Value()  // interface{} which may be nil, string, float64, or bool

// Or just get the value in one step.
gjson.Get(json, "name.last").Value()

To directly access the value from its original type:

result.Type    // can be String, Number, True, False, Null, or JSON
result.Str     // holds the string
result.Num     // holds the float64 number
result.Raw     // holds the raw json

Performance

Benchmarks of GJSON alongside encoding/json, ffjson, and EasyJSON.

BenchmarkGJSONGet-8             3000000    477 ns/op     0 B/op    0 allocs/op
BenchmarkJSONUnmarshalMap-8      600000  10738 ns/op  3176 B/op   69 allocs/op
BenchmarkJSONUnmarshalStruct-8   600000  11635 ns/op  1960 B/op   69 allocs/op
BenchmarkJSONDecoder-8           300000  17193 ns/op  4864 B/op  184 allocs/op
BenchmarkFFJSONLexer-8          1500000   3773 ns/op  1024 B/op    8 allocs/op
BenchmarkEasyJSONLexer-8        3000000   1134 ns/op   741 B/op    6 allocs/op

The JSON document used was:

{
  "widget": {
    "debug": "on",
    "window": {
      "title": "Sample Konfabulator Widget",
      "name": "main_window",
      "width": 500,
      "height": 500
    },
    "image": { 
      "src": "Images/Sun.png",
      "hOffset": 250,
      "vOffset": 250,
      "alignment": "center"
    },
    "text": {
      "data": "Click Here",
      "size": 36,
      "style": "bold",
      "vOffset": 100,
      "alignment": "center",
      "onMouseUp": "sun1.opacity = (sun1.opacity / 100) * 90;"
    }
  }
}

Each operation was rotated though one of the following search paths:

widget.window.name
widget.image.hOffset
widget.text.onMouseUp

These are the results from running the benchmarks on a MacBook Pro 15" 2.8 GHz Intel Core i7:

Contact

Josh Baker @tidwall

License

GJSON source code is available under the MIT License.

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