Serving JSON

Hub › Golang › Beginner › Serving JSON

Goal

Ship the tier exit artifact — a Go program that serves a fixed list of items as JSON at GET /items. After this page you will have a runnable, curl-able HTTP endpoint built entirely from the standard library.

Prerequisites

• Hello HTTP
• JSON encoding

What you're putting together

This page combines two pieces from earlier in the tier:

• net/http listens on a port and routes /items to your handler.
• encoding/json walks the []Item slice and writes it into the response.

The handler sets the Content-Type header so callers know they're getting JSON, then encodes the slice straight into the ResponseWriter.

Code

Create a file called main.go:

package main

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

type Item struct {
	ID    int     `json:"id"`
	Name  string  `json:"name"`
	Price float64 `json:"price"`
}

var items = []Item{
	{ID: 1, Name: "Notebook", Price: 4.0},
	{ID: 2, Name: "Pen", Price: 2.5},
	{ID: 3, Name: "Sticker pack", Price: 5.0},
}

func itemsHandler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	if err := json.NewEncoder(w).Encode(items); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func main() {
	http.HandleFunc("/items", itemsHandler)
	fmt.Println("listening on :8080")
	log.Fatal(http.ListenAndServe(":8080", nil))
}

Run it:

go run main.go

You should see:

listening on :8080

In a second terminal:

curl http://localhost:8080/items

Output:

[{"id":1,"name":"Notebook","price":4},{"id":2,"name":"Pen","price":2.5},{"id":3,"name":"Sticker pack","price":5}]

Stop the server with Ctrl-C.

You shipped a single-endpoint HTTP service with zero third-party dependencies. The whole binary is the Go standard library plus one main.go.

---

You finished a beginner tier. What's next?

Two paths from here.

1. Go deeper on the same platform. The intermediate tier on this same site teaches you to ship a thing that persists, tests itself, and talks to the world. If you liked beginner, that's the natural next step.
2. Pick up an adjacent platform. The table below routes you across platforms based on what you actually want to build.

You just finished	Natural next platform	Why
iOS beginner	iOS intermediate, then Android beginner	Stay native, then learn the other mobile platform with a head start on the Compose/SwiftUI mental model.
Android beginner	Android intermediate, then Golang beginner	Backend-for-frontend pairs naturally with a mobile client.
Golang beginner	AWS beginner, then Golang intermediate	Deploy your endpoint before adding persistence/tests.
Java beginner	Java intermediate, then AWS beginner	JVM persistence + validation first, then deploy.
AWS beginner	Golang beginner	Have a backend to deploy. AWS without a service to host is reference, not curriculum.

Or jump back to the Hub and pick a different goal.