Julia Web Development Guide — Genie, HTTP.jl, and Web Frameworks

In this tutorial, you will learn about Julia Web Development Guide. We cover key concepts, practical examples, and best practices to help you master this topic.

Julia web development options include Genie (full-stack MVC framework), HTTP.jl (low-level HTTP server and client), and OAuth.jl for authentication -- with JSON.jl for data serialization and Mustache.jl for HTML templates.

HTTP Server with Genie

using Genie, Genie.Router, Genie.Requests, Genie.Renderer

# Route
route("/hello") do
    "Hello, World!"
end

route("/hello/:name") do
    name = @params(:name)
    "Hello, $name!"
end

# Start server
Genie.startup(port=8000)

HTTP Client

using HTTP

# GET request
response = HTTP.get("https://api.example.com/data")
println(response.status)
println(String(response.body))

# POST with JSON
body = JSON.json(Dict("name" => "Alice"))
response = HTTP.post("https://api.example.com/users",
    ["Content-Type" => "application/json"],
    body
)

# Query parameters
response = HTTP.get("https://api.example.com/search?q=julia")

JSON Handling

using JSON

# Parse JSON
data = JSON.parse("""{"name": "Alice", "age": 30}""")
println(data["name"])  # Alice

# Encode JSON
person = Dict("name" => "Bob", "age" => 25)
json_str = JSON.json(person)

# Parse from file
data = open("data.json", "r") do io
    JSON.parse(io)
end

REST API

using Genie, Genie.Router, Genie.Requests

Genie.config.cors_allowed_origins = ["*"]

route("/api/users", method=GET) do
    users = [Dict("id" => 1, "name" => "Alice")]
    JSON.json(users)
end

route("/api/users/:id", method=GET) do
    id = parse(Int, @params(:id))
    JSON.json(Dict("id" => id, "name" => "User $id"))
end

Genie.startup(port=8000, async=false)

Common Mistakes

1. Not handling CORS

Browser APIs need CORS headers. Set Genie.config.cors_allowed_origins = ["*"] for development.

2. Blocking the event loop

HTTP.jl is async. Use @async for concurrent requests. Don't block the server with long synchronous operations.

3. Not validating input

Always validate and sanitize user input. Use parse(Int, @params(:id)) with try/catch for bad input.

Practice Questions

1. How do you create a simple route in Genie? route("/path") do ... end. The handler returns the response body.

2. How do you parse JSON response? JSON.parse(String(response.body)) parses the response body as JSON.

3. How do you enable CORS in Genie? Set Genie.config.cors_allowed_origins = ["*"] before starting the server.

FAQ

{{< faq question="What is the fastest Julia web framework?" >}} Oxygen.jl is lightweight and fast for APIs. Genie is more full-featured. HTTP.jl provides the lowest-level control. {{< /faq >}}

{{< faq question="Can I use WebSockets in Julia?" >}} Yes. HTTP.jl supports WebSockets. Genie also provides Websocket support through its channels mechanism. {{< /faq >}}

{{< faq question="How do I serve static files?" >}} Genie automatically serves files from the public/ directory. Configure with Genie.Assets.assets_config(). {{< /faq >}}

What's Next

Now learn about Machine Learning in Julia.