如何获取输入流的CRC并返回此副本

Question

I have one input stream. First I need to get crc of this is what I know how to do eg:

 CRCUtils.getCRC32(IOUtils.toByteArray(is))

I have method in crcUtils which can calculate it from byte array. But then I need this input stream again and I cant use previous one because it reach end. So is there option how to get crc and clone of is ?

Answer 1

You can do it as such:

byte[] byteArr = IOUtils.toByteArray(is);
CRCUtils.getCRC32(byteArr);
InputStream is1 = new ByteArrayInputStream(byteArr); 

Answer 2

您可以在输入流中使用标记 （如果支持）。

Answer 3

如果在处理文件之前不需要CRC值，则还可以创建FilteredInputStream的子类，该子类将读取的所有内容传递给CRC32，并提供一些额外的方法来获取CRC值。

Answer 4

Use CheckedInputStream to compute the CRC while reading a stream:

CRC32 crc = new CRC32();
try (InputStream in = new CheckedInputStream(new FileInputStream("myfile"), crc)) {
    // read the input ...
}
// now crc contains the checksum of the input
long crc32 = crc.getValue();