Does IOUtils.toByteArray(inputStream) method internally close inputStream object?

问题

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

回答1:

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.

回答2:

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);

来源：https://stackoverflow.com/questions/53281591/does-ioutils-tobytearrayinputstream-method-internally-close-inputstream-object

标签

java

inputstream

bytearrayinputstream

ioutils