Develop Reference

InputStream to GZIPInputStream, and I need to know the size of the GZIPInputStream

I have a MultipartFile and I need to compress inputStream as gzip and sent it, but I need to find a way to compress it and know the compressed size of it
param: MultipartFile file
try(var inputStream = file.getInputStream()) {
var outputStream = new GZIPOutputStream(OutputStream.nullOutputStream());
IOUtils.copyLarge(inputStream, outputStream);
var compressedInputStream = someConvertMerthod(outputStream);
sendCompressed(compressedInputStream, compressedSize)
}
Maybe I can do something like this Java: How do I convert InputStream to GZIPInputStream? but I am not gonna be a able to get the compressedSize
I am not finding an easy way to do it :(

CopyLarge() returns the number of bytes copied. I would assume this is true even if the output is discarded, so all you need is to capture the return value of IOUtils.copyLarge(in,out) and you should be good to go, but this does assume the return value is bytes WRITTEN and not bytes READ, which is not really documented. So it might work!
In general though, you are assuming you can turn the output stream back into an input stream, so nullOutputStream() is not going to be an option. Instead you will be creating a temp file, writing your compressed data to it, and then closing it. At that point you can simply ask the file system API how big it is, that should be iron clad.

hey I think I found the solution :)
param: MultipartFile file
try (InputStream inputStream = file.getInputStream()) {
ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
GZIPOutputStream gzipOutputStream = new GZIPOutputStream(byteArrayOutputStream);
inputStream.transferTo(gzipOutputStream);
InputStream compressedInputStream = new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
byteArrayOutputStream.size() // is the compressed size
}
Thanks guys!

How to store file as byte array using FTPClient?

I'm working on FTP-Client tool for connection to ftp.
At this time, I need to upload to ftp via this tool. According to this post and first answer, it's possible to use FileInputStream for saving the files. But i want to store file as a byte array, not FileInputStream.
Is there any way to do that?

Just use a ByteArrayInputStream to wrap the byte array which containes the data you want to upload, and then use this stream in place of the FileInputStream. E.g. something like:
byte[] mydata = <get your data>;
InputStream stream = new ByteArrayInputStream(mydata);
ftpClient.storeFile("remoteName", stream);
stream.close(); // Not strictly needed for ByteArrayInputStream

You can user ByteArrayOutputStream to store byte and can get the byte array.
InputStream baos = new ByteArrayOutputStream();
// write bytes here
baos.write(bytes)
//to get bytes
byte[] bArr = baos.toByteArray();

How can I convert POI HSSFWorkbook to bytes?

Calling Simple toBytes() does produce the bytes but exel throws Warning.
Lost Document information
Googling around gave me this link and looking at Javadocs for worksheet and POI HOW-TO say similar things . Basically I can not get Bytes without loosing some information and should use the write method instead.
While write does work fine I really need to send the bytes over . Is there any way I can do that ? That is get the bytes with out getting any warning .

As that mailing list post said
Invoking HSSFWorkbook.getBytes() does not return all of the data necessary to re-
construct a complete Excel file.
You can use the write method with a ByteArrayOutputStream to get at the byte array.
ByteArrayOutputStream bos = new ByteArrayOutputStream();
try {
workbook.write(bos);
} finally {
bos.close();
}
byte[] bytes = bos.toByteArray();
(The close call is not really needed for a ByteArrayOutputStream, but imho it is good style to include anyway in case its later changed to a different kind of stream.)

How about:
ByteArrayOutputStream baos = new ByteArrayOutputStream();
workbook.write(baos);
byte[] xls = baos.toByteArray();
In order to get a full excel file out, you must call the write(OutputStream) method. If you want bytes from that, just give a ByteArrayOutputStream

Reading the contents of a zip entry from a zip that is in the form of bytes

I'm calling onto some code that returns me an HTTP response. I can get the contents of the response which returns me a byte array. The bytes represent a zip file that I would like to extract and get the contents of a single file (the zip only contains one file).
Currently I have some messy code (I'll need to clean it up if I keep it) that seems to work:
byte[] bytes = response.out.toByteArray();
ByteArrayInputStream input = new ByteArrayInputStream(bytes);
ZipInputStream zip = new ZipInputStream(input);
ByteArrayOutputStream output = new ByteArrayOutputStream();
zip.getNextEntry();
int data;
while ((data = zip.read()) != -1) output.write(data);
output.close();
zip.close();
input.close();
byte[] kmlBytes = output.toByteArray();
String contents = new String(kmlBytes, "UTF-8");
but was wondering whether there was a cleaner way to do the same thing because the above looks incredibly ugly.

In order to avoid "reinventing the wheel" and reduce clutter and to focus on your app's business logic rather than low-level code like this, you can use Apache Commons Compress.

Byte[] to InputStream or OutputStream

I have a blob column in my database table, for which I have to use byte[] in my Java program as a mapping and to use this data I have to convert it to InputStream or OutputStream. But I don't know what happens internally when I do so. Can anyone briefly explain me what's happening when I do this conversion?

You create and use byte array I/O streams as follows:
byte[] source = ...;
ByteArrayInputStream bis = new ByteArrayInputStream(source);
// read bytes from bis ...
ByteArrayOutputStream bos = new ByteArrayOutputStream();
// write bytes to bos ...
byte[] sink = bos.toByteArray();
Assuming that you are using a JDBC driver that implements the standard JDBC Blob interface (not all do), you can also connect a InputStream or OutputStream to a blob using the getBinaryStream and setBinaryStream methods1, and you can also get and set the bytes directly.
(In general, you should take appropriate steps to handle any exceptions, and close streams. However, closing bis and bos in the example above is unnecessary, since they aren't associated with any external resources; e.g. file descriptors, sockets, database connections.)
1 - The setBinaryStream method is really a getter. Go figure.

I'm assuming you mean that 'use' means read, but what i'll explain for the read case can be basically reversed for the write case.
so you end up with a byte[]. this could represent any kind of data which may need special types of conversions (character, encrypted, etc). let's pretend you want to write this data as is to a file.
firstly you could create a ByteArrayInputStream which is basically a mechanism to supply the bytes to something in sequence.
then you could create a FileOutputStream for the file you want to create. there are many types of InputStreams and OutputStreams for different data sources and destinations.
lastly you would write the InputStream to the OutputStream. in this case, the array of bytes would be sent in sequence to the FileOutputStream for writing. For this i recommend using IOUtils
byte[] bytes = ...;//
ByteArrayInputStream in = new ByteArrayInputStream(bytes);
FileOutputStream out = new FileOutputStream(new File(...));
IOUtils.copy(in, out);
IOUtils.closeQuietly(in);
IOUtils.closeQuietly(out);
and in reverse
FileInputStream in = new FileInputStream(new File(...));
ByteArrayOutputStream out = new ByteArrayOutputStream();
IOUtils.copy(in, out);
IOUtils.closeQuietly(in);
IOUtils.closeQuietly(out);
byte[] bytes = out.toByteArray();
if you use the above code snippets you'll need to handle exceptions and i recommend you do the 'closes' in a finally block.

we can convert byte[] array into input stream by using ByteArrayInputStream
String str = "Welcome to awesome Java World";
byte[] content = str.getBytes();
int size = content.length;
InputStream is = null;
byte[] b = new byte[size];
is = new ByteArrayInputStream(content);
For full example please check here http://www.onlinecodegeek.com/2015/09/how-to-convert-byte-into-inputstream.html

There is no conversion between InputStream/OutputStream and the bytes they are working with. They are made for binary data, and just read (or write) the bytes one by one as is.
A conversion needs to happen when you want to go from byte to char. Then you need to convert using a character set. This happens when you make String or Reader from bytes, which are made for character data.

output = new ByteArrayOutputStream();
...
input = new ByteArrayInputStream( output.toByteArray() )

I do realize that my answer is way late for this question but I think the community would like a newer approach to this issue.

byte[] data = dbEntity.getBlobData();
response.getOutputStream().write();
I think this is better since you already have an existing OutputStream in the response object.
no need to create a new OutputStream.