refactor(backend):align with google java standards

backend/src/main/java/com/greenfoxacademy/backend/BackendApplication.java

@@ -3,6 +3,9 @@
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
+/**
+ * This is the main class of the application.
+ */
 @SpringBootApplication
 public class BackendApplication {
 

backend/src/main/java/com/greenfoxacademy/backend/controller/UserController.java

@@ -1,5 +1,9 @@
 package com.greenfoxacademy.backend.controller;
 
+import java.net.URI;
+import java.util.HashMap;
+import java.util.Map;
+
 import com.greenfoxacademy.backend.dtos.RegisterUserDto;
 import com.greenfoxacademy.backend.services.UserService;
 import lombok.RequiredArgsConstructor;
@@ -8,11 +12,12 @@
 import org.springframework.validation.FieldError;
 import org.springframework.validation.annotation.Validated;
 import org.springframework.web.bind.MethodArgumentNotValidException;
-import org.springframework.web.bind.annotation.*;
-
-import java.net.URI;
-import java.util.HashMap;
-import java.util.Map;
+import org.springframework.web.bind.annotation.CrossOrigin;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.bind.annotation.RestController;
 
 
 /**

backend/src/main/java/com/greenfoxacademy/backend/dtos/RegisterResponseDto.java

@@ -1,5 +1,10 @@
 package com.greenfoxacademy.backend.dtos;
 
+
+/**
+ * RegisterResponseDto represents a registration response.
+ * @param id of the created user
+ */
 public record RegisterResponseDto(
         Integer id
 ) {

backend/src/main/java/com/greenfoxacademy/backend/models/User.java

@@ -1,30 +1,34 @@
 package com.greenfoxacademy.backend.models;
 
-import jakarta.persistence.*;
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
 import lombok.NoArgsConstructor;
 
 /**
  * Represents a user entity in the system. This class is a data model
- * that maps to the user table in the database
+ * that maps to the user table in the database.
  */
 @Data
 @Builder
 @AllArgsConstructor
 @NoArgsConstructor
 @Entity
-@Table (name = "_user")
+@Table(name = "_user")
 public class User {
-  
+
   @Id
   @GeneratedValue
   private Integer id;
   private String firstName;
   private String lastName;
-  @Column (unique = true)
+  @Column(unique = true)
   private String email;
   private String password;
-  
+
 }

backend/src/main/java/com/greenfoxacademy/backend/services/PasswordConstraintValidator.java

@@ -7,6 +7,9 @@
 import java.util.ArrayList;
 
 
+/**
+ * Custom validator for password field.
+ */
 public class PasswordConstraintValidator implements ConstraintValidator<ValidPassword, String> {
 
   @Override

backend/src/main/java/com/greenfoxacademy/backend/services/ValidPassword.java

@@ -1,26 +1,39 @@
 package com.greenfoxacademy.backend.services;
 
 
+import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
+import static java.lang.annotation.ElementType.FIELD;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
 import jakarta.validation.Constraint;
 import jakarta.validation.Payload;
-
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;
 
-import static java.lang.annotation.ElementType.*;
-import static java.lang.annotation.RetentionPolicy.RUNTIME;
-
+/**
+ * ValidPassword annotation to mark a field as a password which should be validated.
+ */
 @Documented
 @Constraint (validatedBy = PasswordConstraintValidator.class)
 @Target ({TYPE, FIELD, ANNOTATION_TYPE})
-@Retention (RUNTIME)
+@Retention(RUNTIME)
 public @interface ValidPassword {
-
+
+  /**
+   * Message to be displayed when the password is invalid.
+   */
   String message() default "Invalid Password";
-
+
+  /**
+   * Groups.
+   */
   Class<?>[] groups() default {};
-
+
+  /**
+   * Payload.
+   */
   Class<? extends Payload>[] payload() default {};
 
 }