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();

Java write byte in file

I am doing in Java a File Comprimir to a Binary File. The problem is the next, how can I write a Byte in a new File that the total size only occups 1 byte? I am doing the next:
FileOutputStream saveFile=new FileOutputStream("SaveObj3.sav");
// Create an ObjectOutputStream to put objects into save file.
ObjectOutputStream save = new ObjectOutputStream(saveFile);
save.writeByte(0);
save.close();
saveFile.close();
That, only must to write a only byte in the file, but when I look the size,it occups 7 bytes. Anyone knows how can I write a only byte? Is there another way better?

Don't use ObjectOutputStream. Use the FileOutputStream directly:
FileOutputStream out=new FileOutputStream("SaveObj3.sav");
out.write(0);
out.close();

As JB Nizet noticed documentation of ObjectOutputStream constructor states that this object also
writes the serialization stream header to the underlying stream
which explains additional bytes.
To prevent this behaviour you can just use other streams like FileOutputStream or maybe DataOutputStream
FileOutputStream saveFile = new FileOutputStream("c:/SaveObj3.sav");
DataOutputStream save = new DataOutputStream(saveFile);
save.writeByte(0);
save.close();

You can use Files class provided by Java 7. It's more easy than expected.
It can be performed in one line:
byte[] bytes = new String("message output to be written in file").getBytes();
Files.write(Paths.get("outputpath.txt"), bytes);
If you have a File class, you can just replace:
Paths.get("outputpath.txt")
to:
yourOutputFile.toPath()
To write only one byte, as you want, you can do the following:
Files.write(Paths.get("outputpath.txt"), new byte[1]);
in file properties:
size: 1 bytes

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

Write and read byte[] from file

I'm looking for something simple (no external lib preferably) to write and load a byte[] from a file. More or less something like [Python's pickle][1].
byte[] bytes = new byte[10];
ByteBuffer bbuf = new ByteBuffer.allocate(bytes.length);
bbuf.wrap(bytes); // edited due to Jon Skeet's answer
CharBuffer cbuf = bbuf.asCharBuffer();
cbuf.put("t");
FileOutputStream test = new FileOutputStream("somebytes");
test.write(bytes);
test.close();
The problem seems to be that I cannot read the Object structure from a file like that. In a hex-editor furthermore the file "somebytes" contains just a couple or 0s. So it doesn't seem the FileOutputStream puts any of the content ("t" or the byte-equivalent) into it.
[1] http://wiki.python.org/moin/UsingPickle

You've allocated a byte buffer with the size of bytes, but that doesn't mean the byte buffer is associated with the byte array. You can wrap a byte array using ByteBuffer.wrap.
Here's a minimal change to your code which does write the t into the file:
byte[] bytes = new byte[10];
ByteBuffer bbuf = ByteBuffer.wrap(bytes);
CharBuffer cbuf = bbuf.asCharBuffer();
cbuf.put("t");
FileOutputStream test = new FileOutputStream("somebytes");
test.write(bytes);
test.close();
Note that for real code you should use a try/finally block to make sure the file is always closed regardless of exceptions.
However, this is a long way from serialization. Java does have its own binary serialization - see ObjectOutputStream and ObjectInputStream. Personally I usually avoid this sort of serialization however, as it can be very brittle in the face of changes to classes. There are various other approaches to serialization, such as using Thrift or Protocol Buffers for binary serialization, or serializing to XML, JSON or some other human-readable format.

You can
seek(position)
b = read(length)
Then b will be an array of bytes of your length.
Sorry - on rereading you're looking for writing, not reading.

A simpler version of the same thing is.
byte[] bytes = new byte[10];
bytes[1] = 't';
FileOutputStream test = new FileOutputStream("somebytes");
test.write(bytes);
test.close();
There are plenty of examples on how to read/write byte[] from files on the web. try google.