HT-14 implementation of Pure Rest API

src/main/java/com/example/purerestapi/configuration/ETagConfiguration.java

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+package com.example.purerestapi.configuration;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.filter.ShallowEtagHeaderFilter;
+
+@Configuration
+public class ETagConfiguration {
+
+  @Bean
+  public ShallowEtagHeaderFilter shallowEtagHeaderFilter() {
+    return new ShallowEtagHeaderFilter();
+  }
+}

src/main/java/com/example/purerestapi/controller/RestExceptionHandler.java

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+package com.example.purerestapi.controller;
+
+import com.example.purerestapi.exception.UserNotFoundException;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+
+@org.springframework.web.bind.annotation.ControllerAdvice
+public class RestExceptionHandler {
+
+  @ExceptionHandler(value = {UserNotFoundException.class})
+  protected ResponseEntity<Object> handleConflict(RuntimeException ex) {
+    return ResponseEntity.badRequest().body(ex.getMessage());
+  }
+}

src/main/java/com/example/purerestapi/controller/UserController.java

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+package com.example.purerestapi.controller;
+
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;
+
+import com.example.purerestapi.controller.assembler.NoteAssembler;
+import com.example.purerestapi.controller.assembler.UserAssembler;
+import com.example.purerestapi.entity.Note;
+import com.example.purerestapi.entity.User;
+import com.example.purerestapi.service.UserService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.hateoas.CollectionModel;
+import org.springframework.hateoas.EntityModel;
+import org.springframework.hateoas.IanaLinkRelations;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseBody;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@Controller
+@ResponseBody
+@RequestMapping("/users")
+@RequiredArgsConstructor
+public class UserController {
+
+  private final UserService userService;
+  private final UserAssembler userAssembler;
+  private final NoteAssembler noteAssembler;
+
+  @GetMapping
+  public CollectionModel<EntityModel<User>> getAll() {
+    var users = userService.getAll();
+    return userAssembler.toCollectionModel(users)
+        .add(linkTo(methodOn(UserController.class).getAll()).withSelfRel());
+  }
+
+  @GetMapping("/{id}")
+  public EntityModel<User> getUser(@PathVariable String id) {
+    var user = userService.getUser(id);
+
+    return userAssembler.toModel(user);
+  }
+
+  @PostMapping
+  public ResponseEntity<EntityModel<User>> addUser(@RequestBody User user) {
+    userService.addUser(user);
+    EntityModel<User> entityModel = userAssembler.toModel(user);
+
+    return ResponseEntity
+        .created(entityModel.getRequiredLink(IanaLinkRelations.SELF).toUri())
+        .body(entityModel);
+  }
+
+  @DeleteMapping("/{id}")
+  @ResponseStatus(value = HttpStatus.NO_CONTENT)
+  public void deleteUser(@PathVariable String id) {
+    userService.deleteUser(id);
+  }
+
+  @PostMapping("/{id}/notes")
+  public EntityModel<User> addNote(@PathVariable(name = "id") String userId, @RequestBody Note note) {
+    var user = userService.addNote(userId, note);
+
+    return userAssembler.toModel(user);
+  }
+
+  @GetMapping("/{id}/notes")
+  public CollectionModel<EntityModel<Note>> getUserNotes(@PathVariable(name = "id") String userId) {
+    var notes = userService.getAllNotes(userId);
+    return noteAssembler.toCollectionModel(notes)
+        .add(linkTo(methodOn(UserController.class).getUserNotes(userId)).withSelfRel());
+  }
+}

src/main/java/com/example/purerestapi/controller/assembler/NoteAssembler.java

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+package com.example.purerestapi.controller.assembler;
+
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;
+
+import com.example.purerestapi.controller.UserController;
+import com.example.purerestapi.entity.Note;
+import org.springframework.hateoas.EntityModel;
+import org.springframework.hateoas.server.RepresentationModelAssembler;
+import org.springframework.stereotype.Component;
+
+@Component
+public class NoteAssembler implements RepresentationModelAssembler<Note, EntityModel<Note>> {
+
+  @Override
+  public EntityModel<Note> toModel(Note note) {
+    return EntityModel.of(
+        note,
+        linkTo(methodOn(UserController.class).getUserNotes(note.getUserUuid())).withSelfRel(),
+        linkTo(methodOn(UserController.class).getUser(note.getUserUuid())).withRel("user")
+    );
+  }
+}

src/main/java/com/example/purerestapi/controller/assembler/UserAssembler.java

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+package com.example.purerestapi.controller.assembler;
+
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.linkTo;
+import static org.springframework.hateoas.server.mvc.WebMvcLinkBuilder.methodOn;
+
+import com.example.purerestapi.controller.UserController;
+import com.example.purerestapi.entity.User;
+import org.springframework.hateoas.EntityModel;
+import org.springframework.hateoas.server.RepresentationModelAssembler;
+import org.springframework.stereotype.Component;
+
+@Component
+public class UserAssembler implements RepresentationModelAssembler<User, EntityModel<User>> {
+
+  @Override
+  public EntityModel<User> toModel(User user) {
+    return EntityModel.of(
+        user,
+        linkTo(methodOn(UserController.class).getUser(user.getId())).withSelfRel(),
+        linkTo(methodOn(UserController.class).getAll()).withRel("allUsers"),
+        linkTo(methodOn(UserController.class).getUserNotes(user.getId())).withRel("notes")
+    );
+  }
+}

src/main/java/com/example/purerestapi/entity/Note.java

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+package com.example.purerestapi.entity;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import lombok.Data;
+
+@Data
+public class Note {
+
+  @JsonIgnore
+  private String userUuid;
+  private String subject;
+  private String text;
+}

src/main/java/com/example/purerestapi/entity/User.java

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+package com.example.purerestapi.entity;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.Setter;
+
+@Getter
+@Setter
+public class User {
+
+  private String id;
+  private String firstname;
+  private String surname;
+  @JsonIgnore
+  @Setter(AccessLevel.NONE)
+  private List<Note> notes;
+
+  public void addNote(Note note) {
+    if (notes == null) {
+      notes = new ArrayList<>();
+    }
+    notes.add(note);
+  }
+
+  public List<Note> getNotes() {
+    return Collections.unmodifiableList(notes);
+  }
+
+}

src/main/java/com/example/purerestapi/exception/UserNotFoundException.java

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+package com.example.purerestapi.exception;
+
+public class UserNotFoundException extends RuntimeException {
+
+  public UserNotFoundException() {
+    super("User Not Found");
+  }
+}

src/main/java/com/example/purerestapi/repository/UserRepository.java

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+package com.example.purerestapi.repository;
+
+import com.example.purerestapi.entity.User;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.UUID;
+import java.util.concurrent.ConcurrentHashMap;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public class UserRepository {
+
+  private final static Map<String, User> users = new ConcurrentHashMap<>();
+
+
+  public List<User> getAll() {
+    return users.values().stream().toList();
+  }
+  public void addUser(User user) {
+    if (user.getId() == null) {
+      user.setId(UUID.randomUUID().toString());
+    }
+    if (!users.containsKey(user.getId())) {
+      users.put(user.getId(), user);
+    }
+  }
+
+  public Optional<User> getUser(String id) {
+    return Optional.ofNullable(users.get(id));
+  }
+
+  public void deleteUser(String id) {
+    users.remove(id);
+  }
+}

src/main/java/com/example/purerestapi/service/UserService.java

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+package com.example.purerestapi.service;
+
+import com.example.purerestapi.exception.UserNotFoundException;
+import com.example.purerestapi.entity.Note;
+import com.example.purerestapi.entity.User;
+import com.example.purerestapi.repository.UserRepository;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+public class UserService {
+
+  private final UserRepository userRepository;
+  public void addUser(User user) {
+    userRepository.addUser(user);
+  }
+
+  public User getUser(String id) {
+    return userRepository.getUser(id).orElseThrow(UserNotFoundException::new);
+  }
+
+  public void deleteUser(String id) {
+    userRepository.deleteUser(id);
+  }
+
+  public List<User> getAll() {
+    return userRepository.getAll();
+  }
+
+  public User addNote(String userUuid, Note note) {
+    var user = this.getUser(userUuid);
+
+    note.setUserUuid(userUuid);
+    user.addNote(note);
+    return user;
+  }
+
+  public List<Note> getAllNotes(String userUuid) {
+    var user = this.getUser(userUuid);
+    return user.getNotes() == null ? Collections.emptyList() : user.getNotes();
+  }
+}