Writing and Reading JSON Files

Go offers comprehensive support for JSON encoding and decoding through the encoding/json package. This snippet demonstrates how to write to and read from JSON files efficiently.

Writing JSON to a File

Here's a straightforward example showing how to marshal Go data structures into JSON and write it to a file:

package main

import (
	"encoding/json"
	"os"
)

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

func main() {
	person := Person{Name: "John Doe", Age: 30}
	
	file, err := os.Create("person.json")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	encoder := json.NewEncoder(file)
	if err := encoder.Encode(person); err != nil {
		panic(err)
	}
}

Reading JSON from a File

This example shows how to read and unmarshal JSON data from a file into Go data structures:

package main

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

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

func main() {
	file, err := os.Open("person.json")
	if err != nil {
		panic(err)
	}
	defer file.Close()

	var person Person
	decoder := json.NewDecoder(file)
	if err := decoder.Decode(&person); err != nil {
		panic(err)
	}
	fmt.Printf("Name: %s, Age: %d\n", person.Name, person.Age)
}

Best Practices

• Use json.NewEncoder and json.NewDecoder with files to avoid loading the entire JSON content into memory.
• Define struct types with json tags for seamless JSON marshalling/unmarshalling.
• Always use defer to ensure files are closed.
• Handle errors appropriately; avoid using panic in production code.

Common Pitfalls

• Forgetting to close files, which can lead to resource leaks.
• Not using JSON tags, leading to unexpected JSON output.
• Ignoring error handling, leading to undetected issues.
• Assuming JSON data will always match the expected structure.

Performance Tips

• For large JSON files, stream processing using json.Decoder rather than loading all data into memory with ioutil.ReadFile.
• Use buffered I/O (bufio) for better performance when reading or writing large files.
• Minimize memory footprint by using interface{} for unmarshalling only when necessary, and prefer working with specific data types.