Java: What is the difference between REST and GraphQL?

REST — multiple endpoints, fixed data structure. GraphQL — single endpoint, client-specified data.

REST:

• Multiple endpoints (/users, /posts).
• Fixed response structure.
• Over/under-fetching common.
• HTTP verbs for actions.

1@RestController
2class UserController {
3    @GetMapping("/users/{id}")
4    User getUser(@PathVariable Long id) {
5        return userService.findById(id);
6    }
7}

GraphQL:

• Single /graphql endpoint.
• Client specifies exact fields needed.
• No over-fetching.
• Strongly typed schema.

1type Query {
2  user(id: ID!): User
3}
4type User {
5  id: ID!
6  name: String!
7  posts: [Post!]
8}

When to use:

• REST: simple APIs, caching, broad tooling.
• GraphQL: complex data graphs, mobile clients, rapid iteration.