Java-重置InputStream

问题描述

我正在处理一些Java代码，其中读取了一个InputStream，然后需要使用相同的方法再次读取它.

I'm dealing with some Java code in which there's an InputStream that I read one time and then I need to read it once again in the same method.

问题是我需要将其位置重置为开始才能读取两次.

The problem is that I need to reset it's position to the start in order to read it twice.

我找到了解决该问题的方法:

I've found a hack-ish solution to the problem:

is.mark(Integer.MAX_VALUE);

//Read the InputStream is fully
// { ... }

try
{
    is.reset();
}
catch (IOException e)
{
    e.printStackTrace();
}

此解决方案是否会导致某些无法预期的行为?还是在愚蠢的情况下会起作用?

Does this solution lead to some unespected behaviours? Or it will work in it's dumbness?

推荐答案

按照书面说明，您不能保证，因为不需要 mark()报告其是否成功.要获得保证，您必须先致电 markSupported()，它必须返回 true .

As written, you have no guarantees, because mark() is not required to report whether it was successful. To get a guarantee, you must first call markSupported(), and it must return true.

如所写，指定的读取限制也是非常危险的.如果您碰巧使用的是在内存中缓冲的流，则它可能会分配2GB的缓冲区.另一方面，如果碰巧正在使用 FileInputStream ，就可以了.

Also as written, the specified read limit is very dangerous. If you happen to be using a stream that buffers in-memory, it will potentially allocate a 2GB buffer. On the other hand, if you happen to be using a FileInputStream, you're fine.

更好的方法是将 BufferedInputStream 与显式缓冲区一起使用.

A better approach is to use a BufferedInputStream with an explicit buffer.

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