Java 未捕获 lambda 引发的未经检查的异常

Question

我有一个函数，它接受两个 lambda 作为参数。这些函数抛出一个特定的未经检查的异常，我希望该函数捕获该异常:

    /**
     *
     * @param insert function to insert the entity
     * @param fetch function to fetch the entity
     * @param <T> type of entity being inserted
     * @return
     */
    @Transactional(propagation = Propagation.REQUIRES_NEW, isolation = Isolation.READ_COMMITTED)
    public <T> T getOrInsertWithUniqueConstraints(Supplier<Optional<T>> fetch, Supplier<T> insert) {
        try {
            Optional<T> entity = fetch.get();
            T insertedEntity = entity.orElseGet(insert);
            return insertedEntity;
        }
        catch (Exception e){
            //I expect/want the exception to be caught here, 
            //but this code is never called when debugging
            Optional<T> entityAlreadyInserted = fetch.get();
            return entityAlreadyInserted.get();
        }
    }

在属于另一个事务的函数中调用:

@Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)
...
try {
    Player persistedPlayer = insertOrGetUtil.getOrInsertWithUniqueConstraints(
        () -> playerRepository.findOne(newPlayer.getUsername()),
        //this lambda throws the unchecked DataIntegrityViolationException
        () -> playerRepository.save(newPlayer)
    );
}
catch (Exception e){
    //the exception is caught here for some reason...
}

我是否误解了 Java lambda 的工作原理？另外值得注意的是，代码使用了 Spring 的 @Transactional 和 CrudRepository

Answer 1

异常实际上是在提交事务时发生的，它发生在方法返回之后。为了解决这个问题，我使用 EntityManager#flush() 来触发方法返回之前提交时发生的任何异常:

    @Transactional(propagation = Propagation.REQUIRES_NEW, isolation = Isolation.READ_COMMITTED)
    public <T> T getOrInsertWithUniqueConstraints(Supplier<Optional<T>> fetch, Supplier<T> insert) {
        try {
            Optional<T> entity = fetch.get();
            T insertedEntity = entity.orElseGet(insert);
            entityManager.flush();
            return insertedEntity;
        }
        catch (PersistenceException e){
            DataAccessException dae = persistenceExceptionTranslator.translateExceptionIfPossible(e);
            if (dae instanceof DataIntegrityViolationException){
                Optional<T> entityAlreadyInserted = fetch.get();
                return entityAlreadyInserted.get();
            }
            else {
                throw e;
            }
        }
    }