Java中的Lambda：查找重复id并抛出异常

Question

我想检查一个列表,如果列表中有多个id,则使用lambda表达式抛出异常：

final List<UUID> carUuidList = carRepository.getUuidList(); 

for (int i = 0; i < carUuidList.size(); i++) {
    final UUID carUuid = carUuidList.get(i);
    if(carUuidList.stream().filter(c -> c.equals(carUuid)).collect(Collectors.toList()) > 1){
        //throw exception
    }
}

但它不起作用，我认为有更好的方法使用.orelsethrow(()->...())。那么，如何检查caruuidlist并在有多个UUID的情况下抛出错误呢？

Answer 1

Java9+解决方案具有短路的哈希集<>()::add而不是迭代整个列表的新哈希集<>(list)

List<UUID> carUuidList = carRepository.getUuidList(); 

carUuidList.stream()
           .dropWhile(new HashSet<>()::add)
           .findFirst()
           .ifPresent(dup -> {throw new IllegalArgumentException("duplicate found: " + dup);} );