GJSON
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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). It can also [unmarshal](#unmarshalling) 3 to 4 times faster than the standard Go `json/encoding` unmarshaller. 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 and validates. Invalid 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") } ``` ## Unmarshalling There's a `gjson.Unmarshal` function that loads json data into the value. It's a drop in replacement for `json.Unmarshal` and you can typically see a 3 to 4 times boost in performance without the need for external tools or generators. This function works almost identically to `json.Unmarshal` except that it expects the json to be well-formed prior to being called. Invalid json will not panic, but it may return back unexpected results. Therefore the return value of this function will always be nil. Another difference is that `gjson.Unmarshal` will automatically attempt to convert JSON values to any Go type. For example, the JSON string "100" or the JSON number 100 can be equally assigned to Go string, int, byte, uint64, etc. This rule applies to all types. ```go package main import ( "fmt" "github.com/tidwall/gjson" ) type Animal struct { Type string `json:"type"` Sound string `json:"sound"` Age int `json:"age"` } var json = `{ "type": "Dog", "Sound": "Bark", "Age": "11" }` func main() { var dog Animal gjson.Unmarshal([]byte(json), &dog) fmt.Printf("type: %s, sound: %s, age: %d\n", dog.Type, dog.Sound, dog.Age) } ``` This will print: ``` type: Dog, sound: Bark, age: 11 ``` ## 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 BenchmarkJSONUnmarshalStruct-8 600000 9268 ns/op 1832 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.* ## Contact Josh Baker [@tidwall](http://twitter.com/tidwall) ## License GJSON source code is available under the MIT [License](/LICENSE).