<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"> 
   ... 
</project>

<dependency>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
</dependency>

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>base-project</artifactId>
    <version>0.1.0</version>
    <packaging>pom</packaging>

    <modules>
        <module>book-service</module>
    </modules>

</project>

public class CourseLister {
    // ...

    public List<Course> сoursesByAuthor(String name) {
        List<Course> allCourses = finder.findAll();
        return allCourses
                   .stream()
                   .filter(course -> course.getAuthor().equals(name))
                   .collect(Collectors.toList());
    }
}

public interface CourseFinder {
    List<Course> findAll();
}

public class CourseLister {
    private CourseFinder finder;

    public CourseLister() {
        this.finder = new FileBasedCourseFinder("courses.txt");
    }
    //...
}

@Component
public class CourseLister {
    private final CourseFinder finder;

    @Autowired
    public CourseLister(CourseFinder finder) {
        this.finder = finder;
    }

    public List<Course> сoursesByAuthor(String name) {
        List<Course> allCourses = finder.findAll();
        return allCourses
                   .stream()
                   .filter(course -> course.getAuthor().equals(name))
                   .collect(Collectors.toList());
    }
}

public class Main {
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

public class Main {
    public static void main(String[] args) {
        Class<?> petClass = Pet.class;
        Constructor<?> constructor = pet.getConstructors()[0];
        // экземпляр класса Pet
        Object pet = constructor.newInstance("Барбос", 4);
    }
}

public class Pet {
    public Pet(String name, int age) {
        /* инициализация в конструкторе... */
    }
}

@Component
public class Wife {
    private final Husband husband;

    public Wife(Husband husband) {
        this.husband = husband;
    }
}

@Component
public class Husband {
    private final Wife wife;

    public Husband(Wife wife) {
        this.wife = wife;
    }
}

public class Main {
    public static void main(String[] args) {
        new Wife(
            new Husband(
                /* что подставлять сюда? */
            )
        );
    }
}

@Component
public class Wife {
    private Husband husband;

    @Autowired
    public void setHusband(Husband husband) {
        this.husband = husband;
    }
}

@Component
public class Husband {
    private Wife wife;

    @Autowired
    public void setWife(Wife wife) {
        this.wife = wife;
    }
}

@Component
public class Wife {
    @Autowired
    private Husband husband;
}

@Component
public class Husband {
    @Autowired
    private Wife wife;
}

@Configuration
public class Config {
    @Bean
    public Husband husband() {
        return new Husband();
    }

    @Bean
    public Wife wife() {
        return new Wife();
    }
}

@Component
public class UserServiceImpl implements UserService {
    ...
}

@Component
public class AuditUserService implements UserService {
    @Autowired
    private UserService origin;
    ...
}

@Component
public class EmailUserService implements UserService {
    @Autowired
    private UserService origin;
    ...
}

@Component("userServiceImpl")
public class UserServiceImpl implements UserService {
    ...
}

@Component("auditUserService")
public class AuditUserService implements UserService {
    @Autowired
    @Qualifier("userServiceImpl")
    private UserService origin;
    ...
}

@Component("emailUserService")
public class EmailUserService implements UserService {
    @Autowired
    @Qualifier("auditUserService")
    private UserService origin;
    ...
}

@Component
@Primary
public class EmailUserService implements UserService {
    ...
}

@Service
public class SecurityService {
  public Response authorize(Request request) {
    if (request.getHeader(AUTHORIZATION).startsWith("Basic")) {
      return tryBasicAuth(request);
    }
    if (request.getHeader(AUTHORIZATION).startsWith("Bearer")) {
      return tryJwt(request);
    }
    return new Response(UNAUTHORIZED);
  }
}

public abstract class SecurityService {
  protected SecurityService next;
  
  public void setNext(SecurityService next) {
    this.next = next;
  }
  
  public abstract Response authorize(Request request);
}

@Service
public class BasicAuthSecurityService extends SecurityService {
  
  @Override
  public Response authorize(Request request) {
    if (request.getHeader(AUTHORIZATION).startsWith("Basic")) {
      return tryBasicAuth(request);
    }
    return next.authorize(request);
  }
}

@Service
public class JwtAuthSecurityService extends SecurityService {

  @Override
  public Response authorize(Request request) {
    if (request.getHeader(AUTHORIZATION).startsWith("Bearer")) {
      return tryJwtAuth(request);
    }
    return next.authorize(request);
  }
}

@Service
public class UnauthorizedSecurityService extends SecurityService {

  @Override
  public Response authorize(Request request) {
    return new Response(UNAUTHORIZED);
  }
}

@Service("basic")
public class BasicAuthSecurityService extends SecurityService {
  ...
}

@Service("jwt")
public class JwtAuthSecurityService extends SecurityService {
  ...
}

@Service("unauthorized")
public class UnauthorizedSecurityService extends SecurityService {
  ...
}

@Service
public class SecurityServiceFacade {
  private final SecurityService entry;
  
  public SecurityServiceFacade(Map<String, SecurityService> services) {
    SecurityService basic = services.get("basic"); 
    SecurityService jwt = services.get("jwt"); 
    SecurityService unauthorized = services.get("unauthorized");
    basic.setNext(jwt);
    jwt.setNext(unauthorized);
    this.entry = basic;
  }

  public Response authorize(Request request) {
    return this.entry(request);
  }
}

public abstract class SecurityService {
  protected SecurityService next;
  
  public void setNext(SecurityService next) {
    this.next = next;
  }
  
  public abstract SecurityType getType();
  
  public abstract Response authorize(Request request);
}

@Service
public class BasicAuthSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return BASIC;
  }
}

@Service
public class JwtAuthSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return JWT;
  }
}

@Service
public class UnauthorizedSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return UNAUTHORIZED;
  }
}

@Service
public class SecurityServiceFacade {
  private final SecurityService entry;
  
  public SecurityServiceFacade(List<SecurityService> servicesList) {
    Map<SecurityType, SecurityService> services = 
        servicesList.stream()
                    .collect(toMap(SecurityService::getType, identity()));
    SecurityService basic = services.get(BASIC); 
    SecurityService jwt = services.get(JWT); 
    SecurityService unauthorized = services.get(UNAUTHORIZED);
    basic.setNext(jwt);
    jwt.setNext(unauthorized);
    this.entry = basic;
  }

  public Response authorize(Request request) {
    return this.entry(request);
  }
}

@Service
@Order(0)
public class BasicAuthSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return BASIC;
  }
}

@Service
@Order(1)
public class JwtAuthSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return JWT;
  }
}

@Service
@Order(2)
public class UnauthorizedSecurityService extends SecurityService {
  ...
  public SecurityType getType() {
    return UNAUTHORIZED;
  }
}

@Service
public class SecurityServiceFacade {
  private final SecurityService entry;
  
  public SecurityServiceFacade(List<SecurityService> servicesList) {
    if (servicesList.isEmpty()) {
        throw new IllegalStateException("List cannot be empty");
    }
    for (int i = 1; i < servicesList; i++) {
        SecurityService previous = servicesList.get(i - 1);      
        SecurityService current = servicesList.get(i);
        previous.setNext(current);
    }
    this.entry = servicesList.get(0);
  }

  public Response authorize(Request request) {
    return this.entry(request);
  }
}

Logger logger = LoggerFactory.getLogger(LoggingDemoController.class);

logger.trace("Маршрут выполнения программы");
logger.debug("Отладочное сообщение");
logger.info("Информационное сообщение");
logger.warn("Предупреждение");
logger.error("Сообщение об ошибке");

logging.level.root=TRACE

java -jar myApp-0.0.1-SNAPSHOT.jar --trace

@RestController
@RequestMapping("/api")
public class CourseController {
    private final CourseRepository courseRepository;
    
    public CourseController(CourseRepository courseRepository) {
        this.courseRepository = courseRepository;
    }

    @GetMapping("/courses")
    public List<Course> courseTable() {
        return courseRepository.findAll();
    }
}

[
  {
    "id": 1,
    "author": "Петров А.В.",
    "title": "Основы кройки и шитья"
  },
  {
    "id": 2,
    "author": "Мошкина А.В",
    "title": "Введение в архитектурный дизайн"
  }
]

@Component
public class Listener {
  private final ObjectMapper objectMapper;

  public Listener(ObjectMapper objectMapper) {
    this.objectMapper = objectMapper;
  }

  @EventListener(ApplicationStartedEvent.class)
  public void onApplicationStart() throws Exception {
    String json = objectMapper.writeValueAsString(new Course(1L, "Иван Иванов", "Курс по Java"));
    Course parsedCourse = objectMapper.readValue(json, Course.class);
    // parsedCourse будет таким же, как и изначальный Course
  }
}

public class Course {
    private Long id;
    private String author;
    private String title;
    
    // getters, setters, constructor
}

public interface CourseRepository {
  Optional<Course> findById(Long id);

  List<Course> findAll();
  
  Course save(Course course);
}

@Component
public class InMemoryCourseRepository implements CourseRepository {
   private final List<Course> courses;
   private final AtomicLong idGenerator = new AtomicLong(0);

   public InMemoryCourseRepository() {
     courses = new CopyOnWriteArrayList<>();
     courses.add(new Course(idGenerator.incrementAndGet(), "Петров А.В.", "Основы кройки и шитья"));
     courses.add(new Course(idGenerator.incrementAndGet(), "Мошкина А.В", "Введение в архитектурный дизайн"));
   }

   @Override
   public Optional<Course> findById(Long id) {
     return courses.stream()
                  .filter(c -> c.getId() == id)
                  .findFirst();
   }

   @Override
   public List<Course> findAll() {
     // чтобы случайное изменение в полученном списке не поменяло данные внутри InMemoryCourseRepository
     return new ArrayList<>(courses);
   }

   @Override
   public Course save(Course course) {
     // если id == null, курс новый
     if (course.getId() == null) {
        course.setId(idGenerator.incrementAndGet());
        courses.add(course);
        // чтобы изменение в Course не повлияло на состояние в InMemoryCourseRepository
        return new Course(course);
     }
     // иначе - это операция update
     else {
        synchronized(this) {
            for (Course c : courses) {
              if (c.getId() == course.getId()) {
                c.setAuthor(course.getAuthor());
                c.setName(course.getName());
                return course;
              }
            }
            // иначе курс не найден
            throw new CourseNotFoundException("No course with id=" + course.getId());
        }
     }
   }
}

@RestController
@RequestMapping("/api")
public class CourseController {
    
    @GetMapping("/courses/{id}")
    public Course getCourse(@PathVariable("id") Long id) {
        return courseRepository.findById(id).orElseThrow();
    }
}

public class CourseRequestToUpdate {
  private String author;
  private String title;
  
  // геттеры, сеттеры...
}

@RestController
@RequestMapping("/api")
public class CourseController {
    
    @PutMapping("/courses/{id}")
    public void updateCourse(@PathVariable Long id, 
                             @RequestBody CourseRequestToUpdate request) {
        Course course = courseRepository.findById(id).orElseThrow();
        course.setTitle(request.getTitle());
        course.setAuthor(request.getAuthor());
        courseRepository.save(course);
    }
}

public class CourseRequestToCreate {
  private String author;
  private String title;
  
  // геттеры, сеттеры...
}

@RestController
@RequestMapping("/api")
public class CourseController {
    
    @PostMapping("/courses")
    public Course createCourse(@RequestBody CourseRequestToCreate request) {
        Course course = new Course(request.getTitle(), request.getName());
        return courseRepository.save(course);
    }
}

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

    @DeleteMapping("/courses/{id}")
    public void deleteCourse(@PathVariable Long id) {
        courseRepository.deleteById(id);
    }
}

@ExceptionHandler
public ResponseEntity<ApiError> noSuchElementExceptionHandler(NoSuchElementException ex) {
    return new ResponseEntity<>(
      new ApiError(ex.getMessage()),
      HttpStatus.NOT_FOUND
    );
}

@RestControllerAdvice
public class HandleErrorService {
  
  @ExceptionHandler
  public ResponseEntity<ApiError> noSuchElementExceptionHandler(NoSuchElementException ex) {
    return new ResponseEntity<>(
        new ApiError(ex.getMessage()),
        HttpStatus.NOT_FOUND
    );
  }
}

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-validation</artifactId>
</dependency>

public class CourseRequestToUpdate {

  @NotBlank(message = "Course author has to be filled")
  private String author;
  @NotBlank(message = "Course title has to be filled")
  private String title;

  // геттеры, сеттеры...
}

    @PutMapping("/{id}")
    public void updateCourse(@PathVariable Long id,
                             @Valid @RequestBody CourseRequestToUpdate request) {
    Course course = courseRepository.findById(request.getId()).orElseThrow();
    course.setTitle(request.getTitle());
    course.setAuthor(request.getAuthor());
    courseRepository.save(course);
}