[Enhancement] Remove redundant buffer copy in IoUtils.toByteArray(InputStream)

[nkuprins]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

IoUtils.toByteArray(InputStream) in fesod-common currently looks like this:

public static byte[] toByteArray(final InputStream input) throws IOException {
    final ByteArrayOutputStream output = new ByteArrayOutputStream();
    try {
        copy(input, output);
        return output.toByteArray();
    } finally {
        output.toByteArray();
    }
}

The finally block calls output.toByteArray() and discards the result. ByteArrayOutputStream.toByteArray() allocates a complete copy of the internal buffer, so every call to this method allocates the full data twice.

This method is on real hot paths: WriteWorkbookHolder uses it to read entire template files into memory, and InputStreamImageConverter uses it for image cells. For a large template or image, the transient extra allocation equals the whole payload size (e.g. an extra ~100 MB for a 100 MB template), for no effect.

It appears to be a leftover from translating commons-io's try-with-resources version (IOUtils.toByteArray), where the finally would have been output.close() - a no-op for ByteArrayOutputStream.

Solution

Remove the try/finally entirely, since ByteArrayOutputStream does not need closing:

public static byte[] toByteArray(final InputStream input) throws IOException {
    final ByteArrayOutputStream output = new ByteArrayOutputStream();
    copy(input, output);
    return output.toByteArray();
}

No behavior change - the existing IoUtilsTest cases continue to pass unchanged.

Alternatives

Keep the structure but mirror commons-io with try-with-resources
(try (ByteArrayOutputStream output = new ByteArrayOutputStream())). Functionally
equivalent, since ByteArrayOutputStream.close() is a no-op.

Anything else?

The method is inherited from the EasyExcel lineage; upstream commons-io's
IOUtils.toByteArray uses try-with-resources, which supports the reading that
the finally block was meant to be a close() call.

Are you willing to submit a PR?

• I'm willing to submit a PR!