Encoding Go values to JSON

create-json-01-from-string.go

// Create JSON from a string
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

func main() {
	b, err := json.Marshal("foo")
	if err != nil {
		log.Fatal(err)
	}
	// Prints: "foo"
	fmt.Printf("%s\n", b)
}

create-json-02-from-array.go

// Create JSON from an array
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

func main() {
	b, err := json.Marshal([]string{"foo", "bar", "baz"})
	if err != nil {
		log.Fatal(err)
	}
	// Prints: ["foo","bar","baz"]
	fmt.Printf("%s\n", b)
}

create-json-03-from-map-1.go

// Create JSON from a map
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

func main() {
	m := map[string]int{"foo": 1, "bar": 2, "baz": 3}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"bar":2,"baz":3,"foo":1}
	fmt.Printf("%s\n", b)
}

create-json-04-from-map-2.go

// Create JSON from a map
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

func main() {
	m := map[string]interface{}{
		"name": "Alice",
		"address": map[string]string{
			"street": "Wonder Lane 42",
			"city":   "Wonderland",
		},
		"interests": []string{"K8s", "Go", "JSON"},
	}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"address":{"city":"Wonderland","street":"Wonder Lane 42"},"interests":["K8s","Go","JSON"],"name":"Alice"}
	fmt.Printf("%s\n", b)
}

create-json-05-from-struct-1.go

// Create JSON from a struct
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type Number struct {
	Round  int
	Exact  float64
	hidden string // Not exported (lower case) => not included in JSON
}

func main() {
	m := Number{3, 3.14, "hidden"}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"Round":3,"Exact":3.14}
	fmt.Printf("%s\n", b)
}

create-json-06-from-struct-2.go

// Create JSON from a struct
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type Message struct {
	Name      string
	Address   Address
	Interests []string
	hidden    string // Not exported (lower case) => not included in JSON
}

type Address struct {
	Street string
	City   string
}

func main() {
	m := Message{"Alice", Address{"Wonder Lane 42", "Wonderland"}, []string{"K8s", "Go", "JSON"}, "hidden"}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"Name":"Alice","Address":{"Street":"Wonder Lane 42","City":"Wonderland"},"Interests":["K8s","Go","JSON"]}
	fmt.Printf("%s\n", b)
}

create-json-07-from-struct-with-tags-1.go

// Create JSON from a struct with tags
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type Number struct {
	Round int     `json:"myRound"`
	Exact float64 `json:"myExact"`
}

func main() {
	m := Number{3, 3.14}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"myRound":3,"myExact":3.14}
	fmt.Printf("%s\n", b)
}

create-json-08-from-struct-with-tags-2.go

// Create JSON from a struct with tags
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

// Note: "omitempty" causes field to be skipped if it has an empty value
type Number struct {
	Round int     `json:"myRound"`
	Exact float64 `json:"myExact,omitempty"`
}

func main() {
	n := Number{0, 0.0}
	b, err := json.Marshal(n)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"myRound":0}
	fmt.Printf("%s\n", b)
}

create-json-09-from-struct-with-tags-3.go

// Create JSON from a struct with tags
package main

import (
	"encoding/json"
	"fmt"
	"log"
)

type Message struct {
	Name    string  `json:"name"`
	Address Address `json:"address"`
}

// Note: "string" causes encoding of field as JSON string rather than number
type Address struct {
	Street       string `json:"street"`
	StreetNumber int    `json:"streetNumber,string"`
	City         string `json:"city"`
}

func main() {
	m := Message{"Alice", Address{"Wonder Lane", 42, "Wonderland"}}
	b, err := json.Marshal(m)
	if err != nil {
		log.Fatal(err)
	}
	// Prints: {"name":"Alice","address":{"street":"Wonder Lane","streetNumber":"42","city":"Wonderland"}}
	fmt.Printf("%s\n", b)
}