REST API Basics

@RestController
@RequestMapping("/api")
public class DemoController {

  @GetMapping("/users")
  public List<User> getUsers() {
    return userService.getAllUsers();
  }

}

import org.springframework.web.bind.annotation.*;
import java.util.*;

@RestController
@RequestMapping("/api/users")
public class UserController {

  private List<String> users = new ArrayList<>();

  @GetMapping
  public List<String> getAllUsers() {
    return users;
  }

  @PostMapping
  public String addUser(@RequestBody String user) {
    users.add(user);
    return "User added successfully";
  }

  @PutMapping("/{index}")
  public String updateUser(@PathVariable int index, @RequestBody String user) {
    users.set(index, user);
    return "User updated";
  }

  @DeleteMapping("/{index}")
  public String deleteUser(@PathVariable int index) {
    users.remove(index);
    return "User deleted";
  }

}

// Example Endpoints:
// GET    /api/users
// POST   /api/users
// PUT    /api/users/1
// DELETE /api/users/1

• 1 Web service architecture style.
• 2 Uses HTTP protocol.
• 3 Stateless communication.
• 4 Returns JSON or XML data.

• 1 GET – retrieve data.
• 2 POST – create data.
• 3 PUT – update data.
• 4 DELETE – remove data.

• 1 Stateless.
• 2 Client-server architecture.
• 3 Cacheable responses.
• 4 Uniform interface.

• 1 Easy integration.
• 2 Platform independent.
• 3 Scalable architecture.
• 4 Widely used in modern apps.

• 1 Used in web and mobile app backend services.
• 2 Used in microservices architecture.
• 3 Used in social media APIs.
• 4 Used in banking and fintech systems.
• 5 SaaS products use REST API Basics in Java in services, dashboards, background jobs, and API workflows.
• 6 ERP and banking systems apply REST API Basics in Java with validation, logging, review, and rollback plans.
• 7 E-commerce and healthcare platforms use REST API Basics in Java carefully because reliability and data correctness matter.

• 1 A Java program first evaluates the surrounding context, then applies the REST API Basics in Java rules to the current data.
• 2 The important mental model is input, transformation, result, and failure path.
• 3 In production, the same flow usually sits inside a larger layer such as a controller, service, repository, job, or UI component.

• 1 Choose the simplest implementation first, then measure real workloads.
• 2 Watch for repeated work inside loops, unnecessary allocations, and slow I/O in hot paths.
• 3 Prefer clear data structures and stable APIs before micro-optimizing syntax.

• 1 Treat external input as untrusted until it is validated.
• 2 Avoid hardcoded secrets and never print sensitive values in examples or logs.
• 3 Use established libraries for authentication, encryption, parsing, and database access.

• 1 Not following proper HTTP methods.
• 2 Exposing sensitive data in APIs.
• 3 Ignoring validation and error handling.
• 4 Not using proper status codes.
• 5 Skipping the small working example before adding framework code.
• 6 Ignoring null, empty, duplicate, and boundary inputs.
• 7 Mixing business logic, input handling, and output formatting in one place.
• 8 Using broad error handling that hides the real failure.
• 9 Forgetting to test the behavior after refactoring.
• 10 Adding clever code that future maintainers will struggle to read.

• 1 Use correct HTTP methods (GET, POST, PUT, DELETE).
• 2 Return proper HTTP status codes.
• 3 Validate input data.
• 4 Secure APIs using authentication.
• 5 Start with clear requirements and one minimal working example.
• 6 Use meaningful names that explain business intent.
• 7 Keep examples small enough to debug line by line.
• 8 Validate input at every trust boundary.
• 9 Handle errors explicitly and preserve useful context.
• 10 Prefer simple control flow over deeply nested logic.
• 11 Separate domain logic from I/O and framework code.
• 12 Write tests for normal, boundary, and failure cases.
• 13 Review security assumptions before production use.
• 14 Measure performance before optimizing.
• 15 Document non-obvious decisions close to the code or in project notes.
• 16 Use official documentation when behavior is version-specific.
• 17 Keep dependencies current and remove unused code.
• 18 Avoid hardcoded secrets, credentials, and environment-specific paths.
• 19 Log operational events without exposing sensitive data.
• 20 Design examples so learners can safely modify and rerun them.

• 1 Beginner: rewrite the example with different names and values.
• 2 Intermediate: add validation and handle one expected failure case.
• 3 Advanced: place REST API Basics in Java inside a small service-style design with tests.

• 1 Build a small Java console feature that demonstrates REST API Basics in Java.
• 2 Accept input, process it with the concept, print a clear result, and handle invalid input.
• 3 Add a README note explaining the design choice and two edge cases you tested.

• 1 If the program does not compile, check spelling, imports, braces, and file/class names first.
• 2 If output is unexpected, print intermediate values and verify each branch of the logic.
• 3 If the design feels complex, reduce it to the smallest working example and add pieces back one at a time.

• 1 Practice REST API Basics in Java with a second example from a business domain such as inventory, payroll, banking, or e-commerce.
• 2 Review related Java topics that cover data flow, error handling, testing, and clean design.
• 3 Compare your solution with official documentation and simplify anything you cannot explain clearly.