Rest Controller Basic Implementation

rest-controller.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class CourseResource {
  
  class Course {
    private Long id;
    private String name;
    private String duration;
    
    public Course(Long id, String name, String duration) {
      this.id = id;
      this.name = name;
      this.duration = duration;
    }
    
    public Long getId() {
      return id;
    }
  }
  
  private Map<Long, Course> courses;
 
  public CursoResource() {
    courses = new HashMap<Integer, Course>();
    
    Course c1 = new Course(1, "Workshop Rest", "24hs");
    Course c2 = new Course(2, "Workshop Spring MVC", "24hs");
    Course c3 = new Course(3, "Desenvolvimento Web com JSF 2", "60hs");
    
    courses.put(1, c1);
    courses.put(2, c2);
    courses.put(3, c3);
  }
  
  @GetMapping("/courses")
  public ResponseEntity<List<Course>> findAllCourses() {
    return new ResponseEntity<List<Course>>(new ArrayList<Course>(courses.values()), HttpStatus.OK);
  }

  @GetMapping("/courses/{id}")
  public ResponseEntity<Course> findOne(@PathVariable("id") Integer id) {
    Course course = courses.get(id);
    
    if (course == null) 
      return new ResponseEntity<>(HttpStatus.NOT_FOUND);
    return new ResponseEntity<Course>(course, HttpStatus.OK);
  }
  
  @PostMapping("/courses")
  public ResponseEntity<?> create(@ModelAttribute("course") @Valid Course course) {
    if (courses.containsKey(course.getId())
        return new ResponseEntity<>(HttpStatus.CONFLICT);
        
     courses.put(course.getId(), course);
     return new ResponseEntity<>(HttpStatus.CREATED); 
  }
        
  @PutMapping("/courses/{id}")
  public ResponseEntity<?> update(@PathVariable("id") Long id, Course course) {
    if (!courses.containsKey(course.getId())
        return new ResponseEntity<>(HttpStatus.NOT_FOUND)
        
    courses.put(course.getId(), course);
    return new ResponseEntity<>(HttpStatus.NO_CONTENT);
  }
  
  @DeleteMapping("/courses/{id}")
  public ResponseEntity<?> delete(@PathVariable("id") int id) {
    Course course = courses.remove(id);
 
    if (course == null)
      return new ResponseEntity<>(HttpStatus.NOT_FOUND);
    return new ResponseEntity<>(HttpStatus.NO_CONTENT);
  }