2021-10-09 来源:华纳网 责任编辑:韩玉玲 人气:
核心提示:GJson超快速、方便的JSON解析

知识点:

超快速、方便的JSON解析

 


 

本课内容:

大家好,欢迎来到谷雨课堂,

我们在第19课讲了JSON的使用,

 

在进行没有固定规律的JSON时,

使用上会比较麻烦,

今天我们使用gjson,

来进行各种复杂结构的JSON结构进行解析

 

 

 

以下是全部代码:

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package main
import "github.com/tidwall/gjson"

const json = `{"name":  {"first":"Janet","last":"Prichard"  },"age":47,"rows":[    {"username":"u1","password":"pass1"},    {"username":"u2","password":"pass2"},    {"username":"u3","password":"pass3"},    {"username":"u4","password":"pass4"},    {"username":"u5","password":"pass5"},    {"username":"u6","password":"pass6"},    {"username":"u7","password":"pass7"},    {"username":"u8","password":"pass8"},    {"username":"u9","password":"pass9"},    {"username":"u10","password":"pass10"}  ]}`

func main() {  value := gjson.Get(json, "rows")

  value.ForEach(func(key, v gjson.Result) bool {println(v.Get("username").String())return true  })

}

 

 

扩展阅读:

以下内容来自GJSON官方Github

https://github.com/tidwall/gjson

 

 

Installing

To start using GJSON, install Go and run go get:

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$ 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.

 

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package mainimport "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

result.Indexes        // indexes of all the elements that match on a path containing the '#' query character.

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:

 

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{
  "programmers": [
    {
      "firstName": "Janet", 
      "lastName": "McLaughlin", 
    }, {
      "firstName": "Elliotte", 
      "lastName": "Hunter", 
    }, {
      "firstName": "Jason", 
      "lastName": "Harold", 
    }
  ]
}

 

You would use the path "programmers.#.lastName" like such:

 

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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:

 

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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).

 

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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:

 

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{
  "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

 

 

完整的源代码可以登录【华纳网】下载。

https://www.worldwarner.com/





 





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