根据条件（Java / Guava）从列表中提取第一个匹配项？

我有以下对象的列表：

class ResourcePermissionDTO {
  PermissionType permissionType;
  ... 
}

其中PermissionType是以下枚举：

public enum PermissionType {
   DENY, READ_ONLY, READ_WRITE;
}

因此，列表如下所示：

List<ResourcePermissionDTO> myResourcePermissions = ...

我想要的是返回在myResourcePermissions中找到的第一个ResourcePermissionDTO，它具有最严格的权限。目前，我有以下内容，但有点混乱，尽管使用Google Guava /功能性习语可能有更好的方法？

private ResourcePermissionDTO returnTheFirstMostRestrictivePermissionFoundIn(final List<ResourcePermissionDTO> resourcePermissionDTOs) {
    if (resourcePermissionDTOs.isEmpty()) {
      return null;
    }

    final List<ResourcePermissionDTO> resourcePermissionDTOsWithReadWritePermissionOfDeny = Lists.newArrayList();
    final List<ResourcePermissionDTO> resourcePermissionDTOsWithReadWritePermissionOfReadOnly = Lists.newArrayList();
    final List<ResourcePermissionDTO> resourcePermissionDTOsWithReadWritePermissionOfReadWrite = Lists.newArrayList();

    for (final ResourcePermissionDTO resourcePermissionDTO : resourcePermissionDTOs) {
      switch (resourcePermissionDTO.getPermissionType()) {
      case DENY:
        resourcePermissionDTOsWithReadWritePermissionOfDeny.add(resourcePermissionDTO);
        break;
      case READ_ONLY:
        resourcePermissionDTOsWithReadWritePermissionOfReadOnly.add(resourcePermissionDTO);
        break;
      case READ_WRITE:
        resourcePermissionDTOsWithReadWritePermissionOfReadWrite.add(resourcePermissionDTO);
        break;
      default:
        break;
      }
    }

    if (!resourcePermissionDTOsWithReadWritePermissionOfDeny.isEmpty()) {
      return resourcePermissionDTOsWithReadWritePermissionOfDeny.get(0);
    } else if (!resourcePermissionDTOsWithReadWritePermissionOfReadOnly.isEmpty()) {
      return resourcePermissionDTOsWithReadWritePermissionOfReadOnly.get(0);
    } else if (!resourcePermissionDTOsWithReadWritePermissionOfReadWrite.isEmpty()) {
      return resourcePermissionDTOsWithReadWritePermissionOfReadWrite.get(0);
    } else {
      return null;
    }
  }

轴突

即使是命令式的，也可以将其简化如下：

List<ResourcePermissionDTO> permissions = ...;
ResourcePermissionDTO result = null;

for (ResourcePermissionDTO p: permissions) {
    if (result == null || isStronger(p.getPermissionType(), result.getPermissionType())) {
        result = p;
        if (result.getPermissionType() == PermissionType.DENY) break; // (1)
    }
}

return result;

如果您更喜欢功能样式，则可以使用进行完全相同的复制（尽管没有进行短路优化(1)）reduce()。Guava不支持reduce()，因此以下示例在Java 8中：

return permissions.stream().reduce((result, p) -> {
    return isStronger(p.getPermissionType(), result.getPermissionType()) ? p : result;
}).orElse(null);

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