get a json value quickly
GJSON is a Go package that provides a [fast](#performance) and [simple](#get-a-value) way to get values from a json document. It has features such as [one line retrieval](#get-a-value), [dot notation paths](#path-syntax), [iteration](#iterate-through-an-object-or-array). Getting Started =============== ## Installing To start using GJSON, install Go and run `go get`: ```sh $ 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. Bad json will not panic, but it may return back unexpected results. When the value is found it's returned immediately. ```go 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 [GetMany](#get-multiple-values-at-once) function to get multiple values at once, and [GetBytes](#working-with-bytes) 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 '\\'. ```json { "name": {"first": "Tom", "last": "Anderson"}, "age":37, "children": ["Sara","Alex","Jack"], "fav.movie": "Deer Hunter", "friends": [ {"first": "Dale", "last": "Murphy", "age": 44}, {"first": "Roger", "last": "Craig", "age": 68}, {"first": "Jane", "last": "Murphy", "age": 47} ] } ``` ``` "name.last" >> "Anderson" "age" >> 37 "children" >> ["Sara","Alex","Jack"] "children.#" >> 3 "children.1" >> "Alex" "child*.2" >> "Jack" "c?ildren.0" >> "Sara" "fav\.movie" >> "Deer Hunter" "friends.#.first" >> ["Dale","Roger","Jane"] "friends.1.last" >> "Craig" ``` You can also query an array for the first match by using `#[...]`, or find all matches with `#[...]#`. Queries support the `==`, `!=`, `<`, `<=`, `>`, `>=` comparison operators and the simple pattern matching `%` operator. ``` friends.#[last=="Murphy"].first >> "Dale" friends.#[last=="Murphy"]#.first >> ["Dale","Jane"] friends.#[age>45]#.last >> ["Craig","Murphy"] friends.#[first%"D*"].last >> "Murphy" ``` ## 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: ```go 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.Index // index of raw value in original json, zero means index unknown ``` There are a variety of handy functions that work on a result: ```go result.Exists() bool result.Value() interface{} result.Int() int64 result.Uint() uint64 result.Float() float64 result.String() string result.Bool() bool result.Time() time.Time result.Array() []gjson.Result result.Map() map[string]gjson.Result result.Get(path string) Result result.ForEach(iterator func(key, value Result) bool) result.Less(token Result, caseSensitive bool) bool ``` The `result.Value()` function returns an `interface{}` which requires type assertion and is one of the following Go types: The `result.Array()` function returns back an array of values. If the result represents a non-existent value, then an empty array will be returned. If the result is not a JSON array, the return value will be an array containing one result. ```go 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: ```json { "programmers": [ { "firstName": "Janet", "lastName": "McLaughlin", }, { "firstName": "Elliotte", "lastName": "Hunter", }, { "firstName": "Jason", "lastName": "Harold", } ] } ``` You would use the path "programmers.#.lastName" like such: ```go result := gjson.Get(json, "programmers.#.lastName") for _, name := range result.Array() { println(name.String()) } ``` You can also query an object inside an array: ```go name := gjson.Get(json, `programmers.#[lastName="Hunter"].firstName`) println(name.String()) // prints "Elliotte" ``` ## Iterate through an object or array The `ForEach` function allows for quickly iterating through an object or array. The key and value are passed to the iterator function for objects. Only the value is passed for arrays. Returning `false` from an iterator will stop iteration. ```go result := gjson.Get(json, "programmers") result.ForEach(func(key, value gjson.Result) bool { println(value.String()) return true // keep iterating }) ``` ## 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: ```go 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. ```go 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{}`: ```go 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](https://godoc.org/github.com/tidwall/gjson#GetBytes) function. This is preferred over `Get(string(data), path)`. ```go var json []byte = ... result := gjson.GetBytes(json, path) ``` If you are using the `gjson.GetBytes(json, path)` function and you want to avoid converting `result.Raw` to a `[]byte`, then you can use this pattern: ```go var json []byte = ... result := gjson.GetBytes(json, path) var raw []byte if result.Index > 0 { raw = json[result.Index:result.Index+len(result.Raw)] } else { raw = []byte(result.Raw) } ``` This is a best-effort no allocation sub slice of the original json. This method utilizes the `result.Index` field, which is the position of the raw data in the original json. It's possible that the value of `result.Index` equals zero, in which case the `result.Raw` is converted to a `[]byte`. ## Get multiple values at once The `GetMany` function can be used to get multiple values at the same time, and is optimized to scan over a JSON payload once. ```go results := gjson.GetMany(json, "name.first", "name.last", "age") ``` The return value is a `[]Result`, which will always contain exactly the same number of items as the input paths. ## Performance Benchmarks of GJSON alongside [encoding/json](https://golang.org/pkg/encoding/json/), [ffjson](https://github.com/pquerna/ffjson), [EasyJSON](https://github.com/mailru/easyjson), [jsonparser](https://github.com/buger/jsonparser), and [json-iterator](https://github.com/json-iterator/go) ``` BenchmarkGJSONGet-8 3000000 372 ns/op 0 B/op 0 allocs/op BenchmarkGJSONUnmarshalMap-8 900000 4154 ns/op 1920 B/op 26 allocs/op BenchmarkJSONUnmarshalMap-8 600000 9019 ns/op 3048 B/op 69 allocs/op BenchmarkJSONDecoder-8 300000 14120 ns/op 4224 B/op 184 allocs/op BenchmarkFFJSONLexer-8 1500000 3111 ns/op 896 B/op 8 allocs/op BenchmarkEasyJSONLexer-8 3000000 887 ns/op 613 B/op 6 allocs/op BenchmarkJSONParserGet-8 3000000 499 ns/op 21 B/op 0 allocs/op BenchmarkJSONIterator-8 3000000 812 ns/op 544 B/op 9 allocs/op ``` Benchmarks for the `GetMany` function: ``` BenchmarkGJSONGetMany4Paths-8 4000000 303 ns/op 112 B/op 0 allocs/op BenchmarkGJSONGetMany8Paths-8 8000000 208 ns/op 56 B/op 0 allocs/op BenchmarkGJSONGetMany16Paths-8 16000000 156 ns/op 56 B/op 0 allocs/op BenchmarkGJSONGetMany32Paths-8 32000000 127 ns/op 64 B/op 0 allocs/op BenchmarkGJSONGetMany64Paths-8 64000000 117 ns/op 64 B/op 0 allocs/op BenchmarkGJSONGetMany128Paths-8 128000000 109 ns/op 64 B/op 0 allocs/op ``` JSON document used: ```json { "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 ``` For the `GetMany` benchmarks these paths are used: ``` widget.window.name widget.image.hOffset widget.text.onMouseUp widget.window.title widget.image.alignment widget.text.style widget.window.height widget.image.src widget.text.data widget.text.size ``` *These benchmarks were run on a MacBook Pro 15" 2.8 GHz Intel Core i7 using Go 1.8 and can be be found [here](https://github.com/tidwall/gjson-benchmarks).* ## Contact Josh Baker [@tidwall](http://twitter.com/tidwall) ## License GJSON source code is available under the MIT [License](/LICENSE).