Parsing Json in Go

Go language is a simple, efficient and reliable programming language, and it also provides many convenient libraries and tools when dealing with data. Among them, parsing JSON is a very common task. In this article, we will introduce in detail how to parse JSON in Go language, including the definition of JSON, methods of parsing, sample code and other aspects.

What is JSON?

JSON（JavaScript Object Notation) is a lightweight data exchange format used to pass data between different platforms and languages.JSON formatted data consists of key-value pairs separated by colons between keys and values, commas between key-value pairs, and curly braces wrapping the entire data. Example:

{
    "name": "John",
    "age": 20,
    "address": {
        "province": "Zhejiang",
        "city": "Hangzhou"
    }
}

JSON Parsing Methods in Go

The Go language providesencoding/json package to support JSON parsing and generation. The package contains theMarshal cap (a poem)Unmarshal Two functions for converting Go structs to JSON format and for converting JSON-formatteddata conversionis a Go language struct.

Parsing JSON

We can use the function to parse data in JSON format. The function takes JSON formatted data as input and returns a Go language structure. The sample code is as follows:

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    Name    string
    Age     int
    Address string
}

func main() {
    jsonString := `{"name":"John","age":20,"address":"Hangzhou"}`
    var p Person
    err := json.Unmarshal([]byte(jsonString), &p)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(p.Name, p.Age, p.Address)
}

In the above sample code, we define aPerson structure and parses the JSON-formatted data into this structure. As you can see, we first define a string variablejsonStringwhich contains data in JSON format. Then, we define aPerson variantpand use function willjsonString resolve top in. Finally, we can directly access thep The fields in the

Generate JSON

We can use the function converts Go language structures to JSON formatted data. The function takes a Go language structure as input and returns a JSON formatted string. The sample code is as follows:

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    Name    string
    Age     int
    Address string
}

func main() {
    p := Person{
        Name:    "John",
        Age:     20,
        Address: "Hangzhou",
    }
    jsonString, err := json.Marshal(p)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(string(jsonString))
}

In the above sample code, we define aPerson structure and convert it to JSON format data. As you can see, we first define aPerson variantpand then use the function willp to a JSON-formatted string. Finally, we can use thestring function converts a JSON formatted string to a normal string and outputs the result.

Advanced Usage of JSON Parsing

In addition to the basic JSON parsing methods, the Go language provides some advanced uses for working with JSON data.

Ignore fields that don't exist in JSON

In some cases, JSON data may contain fields that do not exist in Go language constructs. In this case, we can use the functionaljson:"-" tag to ignore these fields. The sample code is as follows:

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    Name    string `json:"name"`
    Age     int    `json:"age"`
    Address string `json:"-"`
    Email   string `json:"email,omitempty"`
}

func main() {
    jsonString := `{"name":"John","age":20,"address":"Hangzhou","phone":"1234567890"}`
    var p Person
    err := json.Unmarshal([]byte(jsonString), &p)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(p.Name, p.Age, p.Address, p.Email)
}

In the above sample code, we define aPerson structure and use thejson:"-" flag to ignore theAddress fields. In addition, we use thejson:"email,omitempty" flag to indicate when theEmail The field is not output when it is empty. As you can see, when we parse the field containing thephone field, the program does not report an error, and theAddress The value of the field is the empty string.Email field is not output.

utilization typology

Sometimes the value of a field in JSON data is a string in JSON format. In this case, we can use the type to represent this field and parse it into a Go language structure if needed. The sample code is as follows:

package main

import (
    "encoding/json"
    "fmt"
)

type Person struct {
    Name    string          `json:"name"`
    Age     int             `json:"age"`
    Address json.RawMessage `json:"address"`
}

type Address struct {
    Province string `json:"province"`
    City     string `json:"city"`
}

func main() {
    jsonString := `{"name":"John","age":20,"address":"{\"province\":\"Zhejiang\",\"city\":\"Hangzhou\"}"}`
    var p Person
    err := json.Unmarshal([]byte(jsonString), &p)
    if err != nil {
        fmt.Println(err)
        return
    }
    var addr Address
    err = json.Unmarshal(p.Address, &addr)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(p.Name, p.Age, addr.Province, addr.City)
}

In the above sample code, we define aPerson structure, whereAddress The type of the field isWhen parsing JSON data, we first parse the JSON data into a single file. When parsing JSON data, we first parse the JSON data into aPerson variantpand then use the function will resolve to anAddress variantaddr. Finally, we can directly access theaddr The fields in the

summarize

This article describes in detail how to parse JSON in Go language, including the definition of JSON, parsing methods, sample code and other aspects. In the actual development, we often need to deal with JSON format data, mastering the JSON parsing method is very important.