gjson

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README

GJSON
Build Status GoDoc GJSON Playground

get a json value quickly

GJSON is a Go package that provides a fast and simple way to get values from a json document. It has features such as one line retrieval, dot notation paths, iteration.

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. Bad 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 GetMany function to get multiple values at once, and GetBytes 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": "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:

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:

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.

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"

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.

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:

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 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:

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.

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, ffjson, EasyJSON, jsonparser, and json-iterator

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:

{
  "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.

Contact

Josh Baker @tidwall

License

GJSON source code is available under the MIT License.

Documentation

Overview

Package gjson provides searching for json strings.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func Unmarshal deprecated 

func Unmarshal(data []byte, v interface{}) error

Unmarshal loads the JSON data into the value pointed to by v.

This function works almost identically to json.Unmarshal except 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.

Deprecated: Use encoder/json.Unmarshal instead

func UnmarshalValidationEnabled deprecated 

func UnmarshalValidationEnabled(enabled bool)

UnmarshalValidationEnabled provides the option to disable JSON validation during the Unmarshal routine. Validation is enabled by default.

Deprecated: Use encoder/json.Unmarshal instead

func Valid 

func Valid(json string) bool

Valid returns true if the input is valid json.

Types

type Result 

type Result struct {
	// Type is the json type
	Type Type
	// Raw is the raw json
	Raw string
	// Str is the json string
	Str string
	// Num is the json number
	Num float64
	// Index of raw value in original json, zero means index unknown
	Index int
}

Result represents a json value that is returned from Get().

func Get 

func Get(json, path string) Result

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.

A path is a series of keys searated 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 character can be escaped with '\'. 

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

func GetBytes 

func GetBytes(json []byte, path string) Result

GetBytes searches json for the specified path. If working with bytes, this method preferred over Get(string(data), path)

func GetMany 

func GetMany(json string, paths ...string) []Result

GetMany searches json for the multiple paths. The return value is a Result array where the number of items will be equal to the number of input paths.

func GetManyBytes 

func GetManyBytes(json []byte, paths ...string) []Result

GetManyBytes searches json for the specified path. If working with bytes, this method preferred over GetMany(string(data), paths...)

func Parse 

func Parse(json string) Result

Parse parses the json and returns a result.

func ParseBytes 

func ParseBytes(json []byte) Result

ParseBytes parses the json and returns a result. If working with bytes, this method preferred over Parse(string(data))

func (Result) Array 

func (t Result) Array() []Result

Array 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.

func (Result) Bool 

func (t Result) Bool() bool

Bool returns an boolean representation.

func (Result) Exists 

func (t Result) Exists() bool

Exists returns true if value exists. 

 if gjson.Get(json, "name.last").Exists(){
		println("value exists")
 }

func (Result) Float 

func (t Result) Float() float64

Float returns an float64 representation.

func (Result) ForEach 

func (t Result) ForEach(iterator func(key, value Result) bool)

ForEach iterates through values. If the result represents a non-existent value, then no values will be iterated. If the result is an Object, the iterator will pass the key and value of each item. If the result is an Array, the iterator will only pass the value of each item. If the result is not a JSON array or object, the iterator will pass back one value equal to the result.

func (Result) Get 

func (t Result) Get(path string) Result

Get searches result for the specified path. The result should be a JSON array or object.

func (Result) Int 

func (t Result) Int() int64

Int returns an integer representation.

func (Result) IsArray 

func (t Result) IsArray() bool

IsArray returns true if the result value is a JSON array.

func (Result) IsObject 

func (t Result) IsObject() bool

IsObject returns true if the result value is a JSON object.

func (Result) Less 

func (t Result) Less(token Result, caseSensitive bool) bool

Less return true if a token is less than another token. The caseSensitive paramater is used when the tokens are Strings. The order when comparing two different type is: 

Null < False < Number < String < True < JSON

func (Result) Map 

func (t Result) Map() map[string]Result

Map returns back an map of values. The result should be a JSON array.

func (Result) String 

func (t Result) String() string

String returns a string representation of the value.

func (Result) Time 

func (t Result) Time() time.Time

Time returns a time.Time representation.

func (Result) Uint 

func (t Result) Uint() uint64

Uint returns an unsigned integer representation.

func (Result) Value 

func (t Result) Value() interface{}

Value returns 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

type Type 

type Type int

Type is Result type 

const (
	// Null is a null json value
	Null Type = iota
	// False is a json false boolean
	False
	// Number is json number
	Number
	// String is a json string
	String
	// True is a json true boolean
	True
	// JSON is a raw block of JSON
	JSON
)

func (Type) String 

func (t Type) String() string

String returns a string representation of the type.

Source Files

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