Java Design Patterns

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目的 ​

当业务事务完成时，所有更新都作为一个大工作单元发送，一次性持久化，以最大程度地减少数据库往返.

解释 ​

现实世界例子

军火商有一个包含武器信息的数据库。当全镇的商家都不断更新这些信息时，会导致数据库服务器的负载很高。 为了使负载更易于管理，我们应用工作单元模式，将许多小更新以批量形式发送.

通俗地讲

Unit of Work 将许多小的数据库更新合并到一个批次中，以优化往返次数。

MartinFowler.com 说

维护受业务事务影响的对象列表，并协调更改的写出和并发问题的解决。

编程实例

这是保存在数据库中的 Weapon 实体.

java
@Getter
@RequiredArgsConstructor
public class Weapon {
    private final Integer id;
    private final String name;
}

实现的基础是实现应用工作单元模式的ArmsDealer。 它维护需要完成的数据库操作的映射（context）并且在提交commit被调用时把它们放在一个批次中.

java
public interface IUnitOfWork<T> {
    
  String INSERT = "INSERT";
  String DELETE = "DELETE";
  String MODIFY = "MODIFY";

  void registerNew(T entity);

  void registerModified(T entity);

  void registerDeleted(T entity);

  void commit();
}

@Slf4j
@RequiredArgsConstructor
public class ArmsDealer implements IUnitOfWork<Weapon> {

    private final Map<String, List<Weapon>> context;
    private final WeaponDatabase weaponDatabase;

    @Override
    public void registerNew(Weapon weapon) {
        LOGGER.info("Registering {} for insert in context.", weapon.getName());
        register(weapon, UnitActions.INSERT.getActionValue());
    }

    @Override
    public void registerModified(Weapon weapon) {
        LOGGER.info("Registering {} for modify in context.", weapon.getName());
        register(weapon, UnitActions.MODIFY.getActionValue());

    }

    @Override
    public void registerDeleted(Weapon weapon) {
        LOGGER.info("Registering {} for delete in context.", weapon.getName());
        register(weapon, UnitActions.DELETE.getActionValue());
    }

    private void register(Weapon weapon, String operation) {
        var weaponsToOperate = context.get(operation);
        if (weaponsToOperate == null) {
            weaponsToOperate = new ArrayList<>();
        }
        weaponsToOperate.add(weapon);
        context.put(operation, weaponsToOperate);
    }

    /**
     * All UnitOfWork operations are batched and executed together on commit only.
     */
    @Override
    public void commit() {
        if (context == null || context.size() == 0) {
            return;
        }
        LOGGER.info("Commit started");
        if (context.containsKey(UnitActions.INSERT.getActionValue())) {
            commitInsert();
        }

        if (context.containsKey(UnitActions.MODIFY.getActionValue())) {
            commitModify();
        }
        if (context.containsKey(UnitActions.DELETE.getActionValue())) {
            commitDelete();
        }
        LOGGER.info("Commit finished.");
    }

    private void commitInsert() {
        var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
        for (var weapon : weaponsToBeInserted) {
            LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
            weaponDatabase.insert(weapon);
        }
    }

    private void commitModify() {
        var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
        for (var weapon : modifiedWeapons) {
            LOGGER.info("Scheduling {} for modification work.", weapon.getName());
            weaponDatabase.modify(weapon);
        }
    }

    private void commitDelete() {
        var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
        for (var weapon : deletedWeapons) {
            LOGGER.info("Scrapping {}.", weapon.getName());
            weaponDatabase.delete(weapon);
        }
    }
}

完整应用程序.

java
// create some weapons
var enchantedHammer = new Weapon(1, "enchanted hammer");
var brokenGreatSword = new Weapon(2, "broken great sword");
var silverTrident = new Weapon(3, "silver trident");

// create repository
var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(), new WeaponDatabase());

// perform operations on the weapons
weaponRepository.registerNew(enchantedHammer);
weaponRepository.registerModified(silverTrident);
weaponRepository.registerDeleted(brokenGreatSword);
weaponRepository.commit();

Here is the console output.

21:39:21.984 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering enchanted hammer for insert in context.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering silver trident for modify in context.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering broken great sword for delete in context.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit started
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Inserting a new weapon enchanted hammer to sales rack.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scheduling silver trident for modification work.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scrapping broken great sword.
21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit finished.

类图 ​

alt text

应用 ​

在以下情况下使用工作单元模式

  • 优化数据库事务的时间.
  • 将更改作为工作单元发送到数据库，以确保事务的原子性.
  • 减少数据库调用次数.

教程 ​

致谢 ​