湿胸你好，今天我测试了一下Data-JPA，想测试一下锁，比如用户注册，当邮箱不存在时，添加数据库。

Repository层

```

public interface UserRepository extends JpaRepository<User, Integer> {

    @Lock(LockModeType.PESSIMISTIC_WRITE)

    Optional<User> findByEmail(String email);

}

```

Service层

```

@Transactional

public User signup(String email, String password) {

    Optional<User> userExists = userRepository.findByEmail(email);

    try {

        Thread.sleep(1000);

    } catch (InterruptedException e) {

        e.printStackTrace();

    }

    if (!userExists.isPresent()) {

        User user = new User();

        user.setEmail(email);

        user.setPassword(password);

         return userRepository.save(user);

    }        

```

UnitTest

```

@Test

public void signupTest() {

    ExecutorService pool = Executors.newFixedThreadPool(2);

    pool.execute(() -> {

        User user = userService.signup("123", "123");

        if (user != null) {

            log.info("用户注册成功");

        }

    });

pool.execute(() -> {

        User user = userService.signup("123", "123");

        if (user != null) {

            log.info("用户注册成功");

        }

    });

    // 这里加上个10秒的sleep

}

```

数据库仍然会插入两条数据。