7.4 KiB
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.
For a command line interface check out JSONed.
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
There's also the GetBytes function for working with JSON byte slices.
Path Syntax
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 or to access a child path, 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",
"friends": [
{"first": "James", "last": "Murphy"},
{"first": "Roger", "last": "Craig"}
]
}
"name.last" >> "Anderson"
"age" >> 37
"children.#" >> 3
"children.1" >> "Alex"
"child*.2" >> "Jack"
"c?ildren.0" >> "Sara"
"fav\.movie" >> "Deer Hunter"
"friends.#.first" >> [ "James", "Roger" ]
"friends.1.last" >> "Craig"
To query an array:
`friends.#[last="Murphy"].first` >> "James"
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 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
result.Multi // holds nested array values
result.Index // index of raw value in original json, zero means index unknown
There are a variety of handy functions that work on a result:
result.Value() interface{}
result.Int() int64
result.Float() float64
result.String() string
result.Bool() bool
result.Array() []gjson.Result
result.Map() map[string]gjson.Result
result.Get(path string) Result
The result.Value() function returns an interface{} which requires type assertion and is one of the following Go types:
boolean >> bool
number >> float64
string >> string
null >> nil
array >> []interface{}
object >> map[string]interface{}
Get nested array values
Suppose you want all the last names from the following json:
{
"programmers": [
{
"firstName": "Janet",
"lastName": "McLaughlin",
}, {
"firstName": "Elliotte",
"lastName": "Hunter",
}, {
"firstName": "Jason",
"lastName": "Harold",
}
]
}`
You would use the path "programmers.#.lastName" like such:
result := gjson.Get(json, "programmers.#.lastName")
for _,name := range result.Array() {
println(name.String())
}
You can also query an object inside an array:
name := gjson.Get(json, `programmers.#[lastName="Hunter"].firstName`)
println(name.String()) // prints "Elliotte"
Simple Parse and Get
There's a Parse(json) function that will do a simple parse, and result.Get(path) that will search a result.
For example, all of these will return the same result:
gjson.Parse(json).Get("name").Get("last")
gjson.Get(json, "name").Get("last")
gjson.Get(json, "name.last")
Check for the existence of a value
Sometimes you just want to know if a value exists.
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")
}
Unmarshal to a map
To unmarshal to a map[string]interface{}:
m, ok := gjson.Parse(json).Value().(map[string]interface{})
if !ok{
// not a map
}
Working with Bytes
If your JSON is contained in a []byte slice, there's the GetBytes function. This is preferred over Get(string(data), path).
var data []byte = ...
res := gjson.GetBytes(data, path)
Performance
Benchmarks of GJSON alongside encoding/json, ffjson, EasyJSON, and jsonparser
BenchmarkGJSONGet-8 15000000 333 ns/op 0 B/op 0 allocs/op
BenchmarkGJSONUnmarshalMap-8 900000 4188 ns/op 1920 B/op 26 allocs/op
BenchmarkJSONUnmarshalMap-8 600000 8908 ns/op 3048 B/op 69 allocs/op
BenchmarkJSONUnmarshalStruct-8 600000 9026 ns/op 1832 B/op 69 allocs/op
BenchmarkJSONDecoder-8 300000 14339 ns/op 4224 B/op 184 allocs/op
BenchmarkFFJSONLexer-8 1500000 3156 ns/op 896 B/op 8 allocs/op
BenchmarkEasyJSONLexer-8 3000000 938 ns/op 613 B/op 6 allocs/op
BenchmarkJSONParserGet-8 3000000 442 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.