feature: Add optimistic offline lock (#1306) (#2551)

optimistic-offline-lock/src/main/java/com/iluwatar/api/UpdateService.java

@@ -0,0 +1,18 @@
+package com.iluwatar.api;
+
+/**
+ * Service for entity update.
+ *
+ * @param <T> target entity
+ */
+public interface UpdateService<T> {
+
+  /**
+   * Update entity.
+   *
+   * @param obj entity to update
+   * @param id  primary key
+   * @return modified entity
+   */
+  T doUpdate(T obj, long id);
+}

optimistic-offline-lock/src/main/java/com/iluwatar/exception/ApplicationException.java

@@ -0,0 +1,16 @@
+package com.iluwatar.exception;
+
+/**
+ * Exception happens in application during business-logic execution.
+ */
+public class ApplicationException extends RuntimeException {
+
+  /**
+   * Inherited constructor with exception message.
+   *
+   * @param message exception message
+   */
+  public ApplicationException(String message) {
+    super(message);
+  }
+}

optimistic-offline-lock/src/main/java/com/iluwatar/model/Card.java

@@ -0,0 +1,37 @@
+package com.iluwatar.model;
+
+
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+/**
+ * Bank card entity.
+ */
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class Card {
+
+  /**
+   * Primary key.
+   */
+  private long id;
+
+  /**
+   * Foreign key points to card's owner.
+   */
+  private long personId;
+
+  /**
+   * Sum of money.
+   */
+  private float sum;
+
+  /**
+   * Current version of object.
+   */
+  private int version;
+}

optimistic-offline-lock/src/main/java/com/iluwatar/repository/JpaRepository.java

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+package com.iluwatar.repository;
+
+/**
+ * Imitation of Spring's JpaRepository.
+ *
+ * @param <T> target database entity
+ */
+public interface JpaRepository<T> {
+
+  /**
+   * Get object by it's PK.
+   *
+   * @param id primary key
+   * @return {@link T}
+   */
+  T findById(long id);
+
+  /**
+   * Get current object version.
+   *
+   * @param id primary key
+   * @return object's version
+   */
+  int getEntityVersionById(long id);
+
+  /**
+   * Update object.
+   *
+   * @param obj entity to update
+   * @return number of modified records
+   */
+  int update(T obj);
+}

optimistic-offline-lock/src/main/java/com/iluwatar/service/CardUpdateService.java

@@ -0,0 +1,35 @@
+package com.iluwatar.service;
+
+import com.iluwatar.api.UpdateService;
+import com.iluwatar.exception.ApplicationException;
+import com.iluwatar.model.Card;
+import com.iluwatar.repository.JpaRepository;
+import lombok.RequiredArgsConstructor;
+
+/**
+ * Service to update {@link Card} entity.
+ */
+@RequiredArgsConstructor
+public class CardUpdateService implements UpdateService<Card> {
+
+  private final JpaRepository<Card> cardJpaRepository;
+
+  @Override
+  public Card doUpdate(Card obj, long id) {
+    float additionalSum = obj.getSum();
+    Card cardToUpdate = cardJpaRepository.findById(id);
+    int initialVersion = cardToUpdate.getVersion();
+    float resultSum = cardToUpdate.getSum() + additionalSum;
+    cardToUpdate.setSum(resultSum);
+    //Maybe more complex business-logic e.g. HTTP-requests and so on
+
+    if (initialVersion != cardJpaRepository.getEntityVersionById(id)) {
+      String exMessage =
+          String.format("Entity with id %s were updated in another transaction", id);
+      throw new ApplicationException(exMessage);
+    }
+
+    cardJpaRepository.update(cardToUpdate);
+    return cardToUpdate;
+  }
+}