Dfyjkt

Here is my code flow for which file content is getting lost and I think may be IOUtils.toByteArray() line is problem, please guide what is actually going wrong here.

File content getting lost :

InputStream stream = someClient.downloadApi(fileId);
byte bytes = IOUtils.toByteArray(stream); 
String mimeType = CommonUtils.fileTypeFromByteArray(bytes);
String fileExtension=FormatToExtensionMapping.getByFormat(mimeType).getExtension();
String filePath = configuration.getDownloadFolder() + "/" ;
String fileName = UUID.randomUUID() + fileExtension; 
File file = new File(filePath+fileName); 
file.createNewFile(); 
FileUtils.copyInputStreamToFile(stream,file); 
int length = (int)file.length();

Now length value here is 0 basically no content. Let me tell you that inputStream received from downloadApi() has content for sure thats given. But if I try below modification in code then I'm getting length of file.

File content NOT getting lost:

InputStream stream = someClient.downloadApi(fileId);
byte bytes = IOUtils.toByteArray(stream);
String mimeType = CommonUtils.fileTypeFromByteArray(bytes);
String fileExtension=FormatToExtensionMapping.getByFormat(mimeType).getExtension();
String filePath = configuration.getDownloadFolder() + "/" ;
String fileName = UUID.randomUUID() + fileExtension;
stream = new ByteArrayInputStream(bytes); //Again converted bytes to stream 
File file = new File(filePath+fileName); 
file.createNewFile(); 
FileUtils.copyInputStreamToFile(stream,file); 
int length = (int)file.length();

Now here I'm getting file content. Can some body tell what is technically wrong here in first code snippet ?

TIA

No it doesn't.

The first version of your code (reproduced below with some added commentary) fails because you are reading from a stream that is already at the end of stream position.

InputStream stream = someClient.downloadApi(fileId);

// This reads the entire stream to the end of stream.
byte bytes = IOUtils.toByteArray(stream);

String mimeType = CommonUtils.fileTypeFromByteArray(bytes);
String fileExtension = 
 FormatToExtensionMapping.getByFormat(mimeType).getExtension();
String filePath = configuration.getDownloadFolder() + "/" ;
String fileName = UUID.randomUUID() + fileExtension; 
File file = new File(filePath+fileName); 
file.createNewFile(); 

// Now you attempt to read more data from the stream.
FileUtils.copyInputStreamToFile(stream,file); 

int length = (int)file.length();

When you try to copy from a stream that is at the end of stream, you get ... zero bytes. And that means you get an empty output file.

No, this stream should be closed.

This is target method of IOUtils:

public static long copyLarge(final InputStream input, final OutputStream output, final byte buffer)
 throws IOException 
 long count = 0;
 int n;
 while (EOF != (n = input.read(buffer))) 
 output.write(buffer, 0, n);
 count += n;
 
 return count;


// create stream and use it
InputStream stream = someClient.downloadApi(fileId);
byte bytes = IOUtils.toByteArray(stream); 

// then us it again
FileUtils.copyInputStreamToFile(stream,file);

// FIXED VERSION
FileUtils.copyInputStreamToFile(new ByteArrayInputStream(bytes),file);