restapi1RestConcepts

1package pkg12restapi;2 3/*4 * restapi1RestConcepts.java5 * -------------------------6 * REST fundamentals: the vocabulary of web APIs (no code to run, just the map).7 *8 * DEFINITION:9 *   REST (REpresentational State Transfer) is an architectural style for APIs10 *   over HTTP. Resources (nouns) are identified by URLs; HTTP methods (verbs)11 *   act on them; representations (JSON/XML) carry their state.12 *13 * THE 6 REST CONSTRAINTS (brief):14 *   1. Client–Server   — separate UI from data storage.15 *   2. Stateless       — each request carries all context (no server session).16 *   3. Cacheable       — responses say if/how they can be cached.17 *   4. Uniform Interface — consistent resource URLs + standard methods.18 *   5. Layered System  — proxies/gateways are transparent.19 *   6. Code on Demand  — (optional) server can ship executable code.20 */21public class restapi1RestConcepts {22 23    public static void main(String[] args) {24        System.out.println("HTTP methods (verbs) and their REST meaning:");25        print("GET",    "read a resource (safe, idempotent)");26        print("POST",   "create a new resource (not idempotent)");27        print("PUT",    "replace a resource (idempotent)");28        print("PATCH",  "partially update a resource");29        print("DELETE", "remove a resource (idempotent)");30 31        System.out.println("\nResource URL design (nouns, plural, hierarchical):");32        System.out.println("  GET    /users           -> list users");33        System.out.println("  GET    /users/42        -> one user");34        System.out.println("  POST   /users           -> create user");35        System.out.println("  PUT    /users/42        -> replace user 42");36        System.out.println("  DELETE /users/42        -> delete user 42");37        System.out.println("  GET    /users/42/orders -> sub-resource");38 39        System.out.println("\nKey status codes:");40        status(200, "OK");          status(201, "Created");41        status(204, "No Content");  status(400, "Bad Request");42        status(401, "Unauthorized");status(403, "Forbidden");43        status(404, "Not Found");   status(409, "Conflict");44        status(422, "Unprocessable Entity"); status(500, "Internal Server Error");45 46        System.out.println("\nCommon headers:");47        System.out.println("  Content-Type: application/json   (what the body IS)");48        System.out.println("  Accept: application/json         (what the client WANTS)");49        System.out.println("  Authorization: Bearer <token>    (who the client IS)");50 51        System.out.println("\nNext: restapi2 builds a server, restapi3 adds CRUD routing,");52        System.out.println("restapi4 handles JSON, restapi5 consumes it with HttpClient.");53    }54 55    static void print(String verb, String meaning) { System.out.printf("  %-7s %s%n", verb, meaning); }56    static void status(int code, String text)       { System.out.printf("  %d %s%n", code, text); }57}