Route Handlers and API Endpoints

Level: Beginner to Intermediate

ℹ️ What You'll Learn

• Creating route handlers in app/api directory
• route.ts file structure (GET, POST, PUT, DELETE)
• NextRequest and NextResponse objects
• Query parameters and URL parsing
• Request body handling and JSON parsing
• HTTP status codes and error responses
• When to use Next.js handlers vs ASP.NET Core
• SMS API gateway pattern

Why This Matters

Route Handlers and API Endpoints is part of building production React applications with Next.js. You will use it when creating student dashboards, SEO-friendly pages, API-connected forms, route handlers, layouts, and deployments for .NET-backed systems.

Next.js can create backend endpoints using route handlers. They live in route.js or route.ts files.

The Problem

Beginners often treat Next.js like plain React and miss routing, rendering, server/client boundaries, environment variables, and deployment behavior. This lesson shows how Route Handlers and API Endpoints works in a real School Management System frontend that talks to ASP.NET Core APIs.

Basic GET Route

app/
  api/
    health/
      route.js

app/api/health/route.js

export async function GET() {
  return Response.json({ status: "ok" });
}

This creates:

GET /api/health

Proxy to ASP.NET Core

Route handlers are useful as a backend-for-frontend layer.

app/api/students/route.js

export async function GET() {
  const apiUrl = process.env.ASP_NET_API_URL;

  const response = await fetch(`${apiUrl}/api/students`, {
    headers: {
      "Accept": "application/json"
    }
  });

  if (!response.ok) {
    return Response.json(
      { message: "Unable to load students" },
      { status: response.status }
    );
  }

  const students = await response.json();
  return Response.json(students);
}

Now the browser can call the Next.js endpoint:

const response = await fetch("/api/students");

POST Route

app/api/students/route.js

export async function POST(request) {
  const student = await request.json();
  const apiUrl = process.env.ASP_NET_API_URL;

  const response = await fetch(`${apiUrl}/api/students`, {
    method: "POST",
    headers: {
      "Content-Type": "application/json"
    },
    body: JSON.stringify(student)
  });

  if (!response.ok) {
    return Response.json(
      { message: "Unable to create student" },
      { status: response.status }
    );
  }

  return Response.json(await response.json(), { status: 201 });
}

When to Use Route Handlers

Good uses:

• Hide backend URLs from the browser
• Attach server-only tokens
• Normalize API responses
• Small backend-for-frontend endpoints
• Webhooks

Use ASP.NET Core for:

• Core business logic
• Database writes
• Complex validation
• Authentication and authorization policy
• Reporting and background jobs

ℹ️ Recommended architecture

Keep ASP.NET Core as the main backend. Use Next.js route handlers only when they simplify frontend integration.

⚠️ Validate twice

A Next.js route handler can validate basic input, but ASP.NET Core should still validate before saving to the database.

Interview Questions

🎯 What is a route handler in Next.js?

A route handler is a server-side endpoint defined with HTTP functions like GET and POST inside a route.js or route.ts file.

🎯 Why use a route handler in front of ASP.NET Core?

It can act as a backend-for-frontend layer for proxying, response shaping, and hiding server-only values from the browser.

Quick Definitions

• Route Handlers and API Endpoints - The main Next.js concept explained in this lesson.
• App Router - The modern Next.js routing system based on the app folder.
• Server/Client boundary - The decision of whether code runs on the server or in the browser.
• ASP.NET Core integration - Calling or proxying backend APIs from a Next.js frontend.

Common Mistakes

• Treating every component as a Client Component without a reason
• Forgetting environment variables differ between local and production
• Calling ASP.NET Core APIs from the browser without handling CORS
• Putting secrets in NEXT_PUBLIC_ variables
• Skipping npm run build before deployment

Practice Task

Create a small Next.js example using Route Handlers and API Endpoints. Keep it connected to a School Management System scenario.

Suggested practice:

1. Create or update a route, layout, form, or data-fetching example.
2. Use realistic student, teacher, attendance, or marks data.
3. Connect the example to an ASP.NET Core-style API URL or route handler.
4. Add one loading, empty, or error state where relevant.
5. Explain what runs on the server and what runs in the browser.

Quick Revision

Question	Answer
What is the main idea?	Use Route Handlers and API Endpoints correctly in a Next.js App Router project.
Where is it used?	Pages, layouts, route handlers, forms, APIs, authentication, and deployment.
What should beginners watch carefully?	Server/client boundaries, environment variables, CORS, and production builds.
What is the best debugging habit?	Check terminal build output, browser console, network tab, and server logs.

🤖Use AI to Learn Faster

⚠️ Important for beginners: Do NOT use AI to write your code yet. Type every example yourself. Your brain learns by doing, not by reading AI output. Use AI only to explain and quiz you — not to code for you. Once you have strong fundamentals, AI becomes a powerful productivity tool for repetitive tasks.

Use ChatGPT, Claude, or Copilot to go deeper on Route Handlers and API Endpoints. Try these prompts:

• "Explain Route Handlers and API Endpoints with a Next.js and ASP.NET Core example"
• "Give me 5 practice tasks for Route Handlers and API Endpoints in a School Management app"
• "Show common Next.js mistakes in Route Handlers and API Endpoints and how to fix them"
• "Quiz me on Route Handlers and API Endpoints with interview-style questions"

💡 Tip: After reading this article, paste your own code into AI and ask "What could go wrong here and why?" — fastest way to find edge cases and deepen understanding.

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