Java 枚举与创建位掩码和检查权限的混淆

发布于 2024-12-29 16:23:00 字数 837 浏览 1 评论 0原文

我想将此 c# 权限模块移植到 java，但是当我无法将数值保存在数据库中然后将其转换为枚举表示形式时，我很困惑如何执行此操作。

在 C# 中，我创建一个像这样的枚举：

public enum ArticlePermission
{
     CanRead   = 1,
     CanWrite  = 2,
     CanDelete = 4,
     CanMove   = 16
}

然后我可以创建一个权限集，如下所示：

ArticlePermission johnsArticlePermission = ArticlePermission.CanRead | ArticlePermission.CanMove;

然后我使用以下方法将其保存到数据库中：

(int)johnsArticlePermission

现在我可以从数据库中将其作为整数/长整型读取，并将其转换为：

johnsArticlePermission = (ArticlePermission) dr["articlePermissions"];

我可以检查权限，例如：

if(johnsArticlePermission & ArticlePermission.CanRead == ArticlePermission.CanRead) 
{

}

How can I do this in java? 据我了解，在java中，您可以将枚举转换为数值，然后将其转换回java枚举。

有想法吗？

原文

I want to port this c# permission module to java, but I am confused how I can do this when I can't save the numeric value in the database and then cast it to the enumeration representation.

In c#, I create a enum like this:

public enum ArticlePermission
{
     CanRead   = 1,
     CanWrite  = 2,
     CanDelete = 4,
     CanMove   = 16
}

I then can create a permission set like:

ArticlePermission johnsArticlePermission = ArticlePermission.CanRead | ArticlePermission.CanMove;

I then save this into the database using:

(int)johnsArticlePermission

Now I can read it from the database as an integer/long, and cast it like:

johnsArticlePermission = (ArticlePermission) dr["articlePermissions"];

And I can check permissions like:

if(johnsArticlePermission & ArticlePermission.CanRead == ArticlePermission.CanRead) 
{

}

How can I do this in java?
From what I understand, in java, you can convert the enumeration into a numeric value, and then convert it back to a java enumeration.

Ideas?

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似狗非友 2025-01-05 16:23:00

您真正需要的是 EnumSet，API中的描述如下：

枚举集在内部表示为位向量。这
表现形式极其紧凑和高效。空间和时间
这个类的性能应该足够好，可以将其用作
传统基于 int 的“位”的高质量、类型安全替代品
标志。”

是一个底层类，因此您可以向其中添加方法。例如，

public enum ArticlePermission
{
  CanRead(1),
  CanWrite(2),
  CanDelete(4),
  CanMove(16); // what happened to 8?

  private int _val;
  ArticlePermission(int val)
  {
    _val = val;
  }

  public int getValue()
  {
    return _val;
  }

  public static List<ArticlePermission> parseArticlePermissions(int val)
  {
    List<ArticlePermission> apList = new ArrayList<ArticlePermission>();
    for (ArticlePermission ap : values())
    {
      if (val & ap.getValue() != 0)
        apList.add(ap);
    }
    return apList;
  }
}

parseArticlePermissions 将为您提供 ArticlePermission 的 List > 来自整数值的对象，大概是通过对 ArticlePermission 对象的值进行或运算创建的。

这里是更详细的 EnumSet 解释。

What you really need here is an EnumSet, described in the API like this:

Enum sets are represented internally as bit vectors. This
representation is extremely compact and efficient. The space and time
performance of this class should be good enough to allow its use as a
high-quality, typesafe alternative to traditional int-based "bit
flags."

An enum is a class under the hood so you can add methods to it. For example,

public enum ArticlePermission
{
  CanRead(1),
  CanWrite(2),
  CanDelete(4),
  CanMove(16); // what happened to 8?

  private int _val;
  ArticlePermission(int val)
  {
    _val = val;
  }

  public int getValue()
  {
    return _val;
  }

  public static List<ArticlePermission> parseArticlePermissions(int val)
  {
    List<ArticlePermission> apList = new ArrayList<ArticlePermission>();
    for (ArticlePermission ap : values())
    {
      if (val & ap.getValue() != 0)
        apList.add(ap);
    }
    return apList;
  }
}

parseArticlePermissions will give you a List of ArticlePermission objects from an integer value, presumably created by ORing the value of ArticlePermission objects.

Here is a more detailed explanation of EnumSet.

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