README

GJSON
GoDoc GJSON Playground

get json values 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, and parsing json lines.

Also check out SJSON for modifying json, and the JJ command line tool.

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". 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

Below is a quick overview of the path syntax, for more complete information please check out GJSON 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, "nets": ["ig", "fb", "tw"]},
    {"first": "Roger", "last": "Craig", "age": 68, "nets": ["fb", "tw"]},
    {"first": "Jane", "last": "Murphy", "age": 47, "nets": ["ig", "tw"]}
  ]
}
"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 % (like) and !% (not like) operators.

friends.#(last=="Murphy").first    >> "Dale"
friends.#(last=="Murphy")#.first   >> ["Dale","Jane"]
friends.#(age>45)#.last            >> ["Craig","Murphy"]
friends.#(first%"D*").last         >> "Murphy"
friends.#(first!%"D*").last        >> "Craig"
friends.#(nets.#(=="fb"))#.first   >> ["Dale","Roger"]

Please note that prior to v1.3.0, queries used the #[...] brackets. This was changed in v1.3.0 as to avoid confusion with the new multipath syntax. For backwards compatibility, #[...] will continue to work until the next major release.

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:

boolean >> bool
number  >> float64
string  >> string
null    >> nil
array   >> []interface{}
object  >> map[string]interface{}

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.

64-bit integers

The result.Int() and result.Uint() calls are capable of reading all 64 bits, allowing for large JSON integers.

result.Int() int64    // -9223372036854775808 to 9223372036854775807
result.Uint() int64   // 0 to 18446744073709551615

Modifiers and path chaining

New in version 1.2 is support for modifier functions and path chaining.

A modifier is a path component that performs custom processing on the json.

Multiple paths can be "chained" together using the pipe character. This is useful for getting results from a modified query.

For example, using the built-in @reverse modifier on the above json document, we'll get children array and reverse the order:

"children|@reverse"           >> ["Jack","Alex","Sara"]
"children|@reverse|0"         >> "Jack"

There are currently the following built-in modifiers:

  • @reverse: Reverse an array or the members of an object.
  • @ugly: Remove all whitespace from a json document.
  • @pretty: Make the json document more human readable.
  • @this: Returns the current element. It can be used to retrieve the root element.
  • @valid: Ensure the json document is valid.
  • @flatten: Flattens an array.
  • @join: Joins multiple objects into a single object.
Modifier arguments

A modifier may accept an optional argument. The argument can be a valid JSON document or just characters.

For example, the @pretty modifier takes a json object as its argument.

@pretty:{"sortKeys":true} 

Which makes the json pretty and orders all of its keys.

{
  "age":37,
  "children": ["Sara","Alex","Jack"],
  "fav.movie": "Deer Hunter",
  "friends": [
    {"age": 44, "first": "Dale", "last": "Murphy"},
    {"age": 68, "first": "Roger", "last": "Craig"},
    {"age": 47, "first": "Jane", "last": "Murphy"}
  ],
  "name": {"first": "Tom", "last": "Anderson"}
}

The full list of @pretty options are sortKeys, indent, prefix, and width. Please see Pretty Options for more information.

Custom modifiers

You can also add custom modifiers.

For example, here we create a modifier that makes the entire json document upper or lower case.

gjson.AddModifier("case", func(json, arg string) string {
  if arg == "upper" {
    return strings.ToUpper(json)
  }
  if arg == "lower" {
    return strings.ToLower(json)
  }
  return json
})
"children|@case:upper"           >> ["SARA","ALEX","JACK"]
"children|@case:lower|@reverse"  >> ["jack","alex","sara"]

JSON Lines

There's support for JSON Lines using the .. prefix, which treats a multilined document as an array.

For example:

{"name": "Gilbert", "age": 61}
{"name": "Alexa", "age": 34}
{"name": "May", "age": 57}
{"name": "Deloise", "age": 44}
..#                   >> 4
..1                   >> {"name": "Alexa", "age": 34}
..3                   >> {"name": "Deloise", "age": 44}
..#.name              >> ["Gilbert","Alexa","May","Deloise"]
..#(name="May").age   >> 57

The ForEachLines function will iterate through JSON lines.

gjson.ForEachLine(json, func(line gjson.Result) bool{
    println(line.String())
    return true
})

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")
}

Validate JSON

The Get* and Parse* functions expects that the json is well-formed. Bad json will not panic, but it may return back unexpected results.

If you are consuming JSON from an unpredictable source then you may want to validate prior to using GJSON.

if !gjson.Valid(json) {
	return errors.New("invalid json")
}
value := gjson.Get(json, "name.last")

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.

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

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 through 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 1.8 and can be found here.

Expand ▾ Collapse ▴

Documentation

Overview

    Package gjson provides searching for json strings.

    Index

    Constants

    This section is empty.

    Variables

    View Source
    var DisableModifiers = false

      DisableModifiers will disable the modifier syntax

      Functions

      func AddModifier

      func AddModifier(name string, fn func(json, arg string) string)

        AddModifier binds a custom modifier command to the GJSON syntax. This operation is not thread safe and should be executed prior to using all other gjson function.

        func ForEachLine

        func ForEachLine(json string, iterator func(line Result) bool)

          ForEachLine iterates through lines of JSON as specified by the JSON Lines format (http://jsonlines.org/). Each line is returned as a GJSON Result.

          func ModifierExists

          func ModifierExists(name string, fn func(json, arg string) string) bool

            ModifierExists returns true when the specified modifier exists.

            func Valid

            func Valid(json string) bool

              Valid returns true if the input is valid json.

              if !gjson.Valid(json) {
              	return errors.New("invalid json")
              }
              value := gjson.Get(json, "name.last")
              

              func ValidBytes

              func ValidBytes(json []byte) bool

                ValidBytes returns true if the input is valid json.

                if !gjson.Valid(json) {
                	return errors.New("invalid json")
                }
                value := gjson.Get(json, "name.last")
                

                If working with bytes, this method preferred over ValidBytes(string(data))

                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". When the value is found it's returned immediately.

                    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 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"]
                    

                    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. If you are consuming JSON from an unpredictable source then you may want to use the Valid function first.

                    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, path ...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, path ...string) []Result

                          GetManyBytes 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 Parse

                          func Parse(json string) Result

                            Parse parses the json and returns a result.

                            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. If you are consuming JSON from an unpredictable source then you may want to use the Valid function first.

                            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
                                                            map[string]interface{}, for JSON objects
                                                            []interface{}, for JSON arrays
                                                            

                                                            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