Java ObjectOutputStream 和更新文件
我无法解决一个实现问题，我有一个类，它的行为类似于列表，但不是将文件保存在某个集合中，而是将它们保存在磁盘上。
当我想向列表中添加一些元素时，就会出现问题。在文件的开头，我有一个 int 告诉我列表中有多少个对象，但我无法找出更新该值的优雅方法。我有这样的东西：
public boolean add(T element)
{
try
{
out.writeObject(element);
out.flush();
//and here we need to update the int in my file
} catch (IOException e)
{
e.printStackTrace();
}
return true;
}
我尝试使用这样的东西：
ObjectOutputStream upd=new ObjectOutputStream(new FileOutputStream(data.getAbsolutePath(),true));
但据我观察，它会将一些数据写入文件的开头，一些序列化标头或其他东西，我如何更新文件中的单个条目或如何更改
ObjectOutputStream
“指针” “写在文件的开头？
I am having trouble figuring out one implementation problem, I have one class, it behaves like list but instead of holding a file in some collection it saves them on a disk.
The problem occurs when I want to add some element to my list. At the start of my file I have one int that tells me how many objects there are in my list, but I can't figure out elegant way to update this value. I have something like this:
public boolean add(T element)
{
try
{
out.writeObject(element);
out.flush();
//and here we need to update the int in my file
} catch (IOException e)
{
e.printStackTrace();
}
return true;
}
I tried to use something like this:
ObjectOutputStream upd=new ObjectOutputStream(new FileOutputStream(data.getAbsolutePath(),true));
but as I observed it writes some data to the start of the file, some serialization header or sth, how can I update single entry in my file or how to change
ObjectOutputStream
"pointer" to write at the beginning of the file?
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通常，对于基于流的类（尤其是像 OOS 这样的高阶流），您应该在每次更新文件时重写整个文件。
如果您确实坚持只更新文件的一部分，那么您应该将该文件视为由 N 个流组成，其中每个“流”代表您正在写入的一个对象。所以我会使用 RandomAccessFile 作为基本文件，然后当我想写入一个对象时，我会将 ObjectOutputStream 包装在 ByteArrayOutputStream 之上，将对象写入其中，然后获取这些字节，并将这些字节重写到 RandomAcessFile 中，其中你想要的。
这可能不会特别有效，因为您将为正在编写的对象编写 N 个 OOS 标头和 N 个类描述。
Typically with stream based classes (especially higher order streams like OOS), you should rewrite the whole file, anytime you update it.
If you really INSIST on only updating part of a file, then you should think of the file as made up of N streams, where each 'stream' represents one object that you are writing. So i would use a RandomAccessFile for the base file, and then when i want to write an object i would wrap an ObjectOutputStream on top of a ByteArrayOutputStream, write your object into that, then take those bytes, and rewrite those bytes into the RandomAcessFile where you want.
This probably won't be particularly efficient, as you will write N OOS headers, and N class descriptions for the object you are writing.