Go: parsing a JSON file

  • Go
  • Gabriele Romanato

Parsing JSON files is one of the most common operations when working with structured data in Go. JSON (JavaScript Object Notation) is a widely used data format for exchanging information between applications. Go provides a standard encoding/json package that offers a wide range of functionality for manipulating JSON data.

Lets start by importing the encoding/json package into our Go program: 


    package main

    import (
        "encoding/json"
        "fmt"
        "io/ioutil"
        "os"
    )

The next step is to read the contents of the JSON file. We can use the ioutil.ReadFile function to get the file content as a byte array: 


    func main() {
        filePath := "data.json"
    
        // Leggi il contenuto del file
        data, err := ioutil.ReadFile(filePath)
        if err != nil {
            fmt.Println("Errore nella lettura del file:", err)
            return
        }
    }

Now that we have the contents of the file, we can start parsing the JSON. We use the json.Unmarshal function to convert the JSON data into a corresponding Go data structure. We need to define a Go structure that represents the structure of the JSON: 


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

Next, we parse the JSON data using the json.Unmarshal function: 


    // Effettua il parsing dei dati JSON
    var person Person
    err = json.Unmarshal(data, &person)
    if err != nil {
        fmt.Println("Errore nel parsing del JSON:", err)
        return
    }

Now the JSON data has been converted into the person structure of type Person . We can access individual data fields as usual: 


    fmt.Println("Nome:", person.Name)
    fmt.Println("Età:", person.Age)
    fmt.Println("Email:", person.Email)

If the JSON file contains an array of objects, we can use a slice to store the data. For example, if the JSON file contains an array of people, we can define a structure like this: 


    type Person struct {
        Name  string `json:"name"`
        Age   int    `json:"age"`
        Email string `json:"email"`
    }
    
    type People struct {
        People []Person `json:"people"`
    }

And then parse the JSON as follows: 


    // Effettua il parsing dei dati JSON
    var people People
    err = json.Unmarshal(data, &people)
    if err != nil {
        fmt.Println("Errore nel parsing del JSON:", err)
        return
    }
    
    // Stampa i dati
    for _, p := range people.People {
        fmt.Println("Nome:", p.Name)
        fmt.Println("Età:", p.Age)
        fmt.Println("Email:", p.Email)
        fmt.Println()
    }

This for loop prints each persons data to the JSON file.

Finally, remember to handle errors when parsing the JSON. If the JSON is invalid or does not match the defined structure, the json.Unmarshal function will return an error. Make sure you check and handle errors properly in your code.

Parsing JSON files in Go is quite simple thanks to the encoding/json package provided by the language. By following the steps described above, you will be able to parse JSON data in a few simple steps and work with it in your Go program.

Back to top