feat: added notification pattern (#2629)

Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>

notification/src/main/java/com/iluwatar/App.java

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+package com.iluwatar;
+
+import java.time.LocalDate;
+
+/**
+ * The notification pattern captures information passed between layers, validates the information, and returns
+ * any errors to the presentation layer if needed.
+ *
+ * <p>In this code, this pattern is implemented through the example of a form being submitted to register
+ * a worker. The worker inputs their name, occupation, and date of birth to the RegisterWorkerForm (which acts
+ * as our presentation layer), and passes it to the RegisterWorker class (our domain layer) which validates it.
+ * Any errors caught by the domain layer are then passed back to the presentation layer through the
+ * RegisterWorkerDto.</p>
+ */
+public class App {
+
+  private static final String NAME = "";
+  private static final String OCCUPATION = "";
+  private static final LocalDate DATE_OF_BIRTH = LocalDate.of(2016, 7, 13);
+
+  public static void main(String[] args) {
+    var form = new RegisterWorkerForm(NAME, OCCUPATION, DATE_OF_BIRTH);
+    form.submit();
+  }
+
+}

notification/src/main/java/com/iluwatar/DataTransferObject.java

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+package com.iluwatar;
+
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+/**
+ * Layer super type for all Data Transfer Objects.
+ * Also contains code for accessing our notification.
+ */
+@Getter
+@NoArgsConstructor
+public class DataTransferObject {
+
+  private final Notification notification = new Notification();
+
+}

notification/src/main/java/com/iluwatar/Notification.java

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+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.List;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+/**
+ * The notification. Used for storing errors and any other methods
+ * that may be necessary for when we send information back to the
+ * presentation layer.
+ */
+@Getter
+@NoArgsConstructor
+public class Notification {
+
+  private final List<NotificationError> errors = new ArrayList<>();
+
+  public boolean hasErrors() {
+    return !this.errors.isEmpty();
+  }
+
+  public void addError(NotificationError error) {
+    this.errors.add(error);
+  }
+}

notification/src/main/java/com/iluwatar/NotificationError.java

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+package com.iluwatar;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+
+/**
+ * Error class for storing information on the error.
+ * Error ID is not necessary, but may be useful for serialisation.
+ */
+@Getter
+@AllArgsConstructor
+public class NotificationError {
+  private int errorId;
+  private String errorMessage;
+
+  @Override
+  public String toString() {
+    return "Error " + errorId + ": " + errorMessage;
+  }
+}

notification/src/main/java/com/iluwatar/RegisterWorker.java

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+package com.iluwatar;
+
+import java.time.LocalDate;
+import java.time.Period;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * Class which handles actual internal logic and validation for worker registration.
+ * Part of the domain layer which collects information and sends it back to the presentation.
+ */
+@Slf4j
+public class RegisterWorker extends ServerCommand {
+  static final int LEGAL_AGE = 18;
+  protected RegisterWorker(RegisterWorkerDto worker) {
+    super(worker);
+  }
+
+  /**
+   * Validates the data provided and adds it to the database in the backend.
+   */
+  public void run() {
+
+    validate();
+    if (!super.getNotification().hasErrors()) {
+      LOGGER.info("Register worker in backend system");
+    }
+  }
+
+  /**
+   * Validates our data. Checks for any errors and if found, adds to notification.
+   */
+  private void validate() {
+    var ourData = ((RegisterWorkerDto) this.data);
+    //check if any of submitted data is not given
+    // passing for empty value validation
+    fail(isNullOrBlank(ourData.getName()), RegisterWorkerDto.MISSING_NAME);
+    fail(isNullOrBlank(ourData.getOccupation()), RegisterWorkerDto.MISSING_OCCUPATION);
+    fail(isNullOrBlank(ourData.getDateOfBirth()), RegisterWorkerDto.MISSING_DOB);
+
+    if (isNullOrBlank(ourData.getDateOfBirth())) {
+      // If DOB is null or empty
+      fail(true, RegisterWorkerDto.MISSING_DOB);
+    } else {
+      // Validating age ( should be greater than or equal to 18 )
+      Period age = Period.between(ourData.getDateOfBirth(), LocalDate.now());
+      fail(age.getYears() < LEGAL_AGE, RegisterWorkerDto.DOB_TOO_SOON);
+    }
+  }
+
+  /**
+   * Validates for null/empty value.
+   *
+   * @param obj any object
+   * @return boolean
+   */
+  protected boolean isNullOrBlank(Object obj) {
+    if (obj == null) {
+      return true;
+    }
+
+    if (obj instanceof String) {
+      return ((String) obj).trim().isEmpty();
+    }
+
+    return false;
+  }
+
+  /**
+   * If a condition is met, adds the error to our notification.
+   *
+   * @param condition condition to check for.
+   * @param error     error to add if condition met.
+   */
+  protected void fail(boolean condition, NotificationError error) {
+    if (condition) {
+      super.getNotification().addError(error);
+    }
+  }
+}

notification/src/main/java/com/iluwatar/RegisterWorkerDto.java

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+package com.iluwatar;
+
+import java.time.LocalDate;
+import lombok.Getter;
+import lombok.Setter;
+
+/**
+ * Data transfer object which stores information about the worker. This is carried between
+ * objects and layers to reduce the number of method calls made.
+ */
+@Getter
+@Setter
+public class RegisterWorkerDto extends DataTransferObject {
+  private String name;
+  private String occupation;
+  private LocalDate dateOfBirth;
+
+  /**
+   * Error for when name field is blank or missing.
+   */
+  public static final NotificationError MISSING_NAME =
+          new NotificationError(1, "Name is missing");
+
+  /**
+   * Error for when occupation field is blank or missing.
+   */
+  public static final NotificationError MISSING_OCCUPATION =
+          new NotificationError(2, "Occupation is missing");
+
+  /**
+   * Error for when date of birth field is blank or missing.
+   */
+  public static final NotificationError MISSING_DOB =
+          new NotificationError(3, "Date of birth is missing");
+
+  /**
+   * Error for when date of birth is less than 18 years ago.
+   */
+  public static final NotificationError DOB_TOO_SOON =
+          new NotificationError(4, "Worker registered must be over 18");
+
+
+  protected RegisterWorkerDto() {
+    super();
+  }
+
+  /**
+   * Simple set up function for capturing our worker information.
+   *
+   * @param name        Name of the worker
+   * @param occupation  occupation of the worker
+   * @param dateOfBirth Date of Birth of the worker
+   */
+  public void setupWorkerDto(String name, String occupation, LocalDate dateOfBirth) {
+    this.name = name;
+    this.occupation = occupation;
+    this.dateOfBirth = dateOfBirth;
+  }
+}

notification/src/main/java/com/iluwatar/RegisterWorkerForm.java

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+package com.iluwatar;
+
+import java.time.LocalDate;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * The form submitted by the user, part of the presentation layer,
+ * linked to the domain layer through a data transfer object and
+ * linked to the service layer directly.
+ */
+@Slf4j
+public class RegisterWorkerForm {
+  String name;
+  String occupation;
+  LocalDate dateOfBirth;
+  RegisterWorkerDto worker;
+  RegisterWorkerService service = new RegisterWorkerService();
+
+  /**
+   *  Constructor.
+   *
+   * @param name        Name of the worker
+   * @param occupation  occupation of the worker
+   * @param dateOfBirth Date of Birth of the worker
+   */
+  public RegisterWorkerForm(String name, String occupation, LocalDate dateOfBirth) {
+    this.name = name;
+    this.occupation = occupation;
+    this.dateOfBirth = dateOfBirth;
+  }
+
+  /**
+   * Attempts to submit the form for registering a worker.
+   */
+  public void submit() {
+    //Transmit information to our transfer object to communicate between layers
+    saveToWorker();
+    //call the service layer to register our worker
+    service.registerWorker(worker);
+
+    //check for any errors
+    if (worker.getNotification().hasErrors()) {
+      indicateErrors();
+      LOGGER.info("Not registered, see errors");
+    } else {
+      LOGGER.info("Registration Succeeded");
+    }
+  }
+
+  /**
+   * Saves worker information to the data transfer object.
+   */
+  private void saveToWorker() {
+    worker = new RegisterWorkerDto();
+    worker.setName(name);
+    worker.setOccupation(occupation);
+    worker.setDateOfBirth(dateOfBirth);
+  }
+
+  /**
+   * Check for any errors with form submission and show them to the user.
+   */
+  public void indicateErrors() {
+    worker.getNotification().getErrors().forEach(error -> LOGGER.error(error.toString()));
+  }
+}

notification/src/main/java/com/iluwatar/RegisterWorkerService.java

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+package com.iluwatar;
+
+/**
+ * Service used to register a worker.
+ * This represents the basic framework of a service layer which can be built upon.
+ */
+public class RegisterWorkerService {
+  /**
+   * Creates and runs a command object to do the work needed,
+   * in this case, register a worker in the system.
+   *
+   * @param registration worker to be registered if possible
+   */
+  public void registerWorker(RegisterWorkerDto registration) {
+    var cmd = new RegisterWorker(registration);
+    cmd.run();
+  }
+}

notification/src/main/java/com/iluwatar/ServerCommand.java

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+package com.iluwatar;
+
+import lombok.AllArgsConstructor;
+
+/**
+ * Stores the dto and access the notification within it.
+ * Acting as a layer supertype in this instance for the domain layer.
+ */
+@AllArgsConstructor
+public class ServerCommand {
+  protected DataTransferObject data;
+
+  /**
+   * Basic getter to extract information from our data.
+   *
+   * @return the notification stored within the data
+   */
+  public Notification getNotification() {
+    return data.getNotification();
+  }
+}