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 efficient 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 validates. 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 separated 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. The dot and wildcard characters can be escaped with ''.

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

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:

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

To get the Go 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:

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

Check for the existence of a value

Sometimes you may want to see if the value actually existed in the json document.

value := gjson.Get(json, "name.last")
if !value.Exists() {
	println("no last name")
} else {
	println(value.String())
}

// Or as one step
if gjson.Get(json, "name.last").Exists(){
	println("has a last name")
}

Performance

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

BenchmarkGJSONGet-8              	 3000000	       373 ns/op	       0 B/op	       0 allocs/op
BenchmarkJSONUnmarshalMap-8      	  600000	      8884 ns/op	    3048 B/op	      69 allocs/op
BenchmarkJSONUnmarshalStruct-8   	  600000	      9045 ns/op	    1832 B/op	      69 allocs/op
BenchmarkJSONDecoder-8           	  300000	     14134 ns/op	    4224 B/op	     184 allocs/op
BenchmarkFFJSONLexer-8           	 1500000	      3182 ns/op	     896 B/op	       8 allocs/op
BenchmarkEasyJSONLexer-8         	 3000000	       932 ns/op	     613 B/op	       6 allocs/op
BenchmarkJSONParserGet-8         	 3000000	       444 ns/op	      21 B/op	       0 allocs/op

JSON document used:

{
  "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 benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.7.

Contact

Josh Baker @tidwall

License

GJSON source code is available under the MIT License.