Writing a File object to a file in java

Question

For a class, I have to send a file of any type from my client to a server. I have to handle each packet individually and use UDP. I have managed to transfer the file from the client to the server, and I now have a file object which I cannot figure out how to save to a user specified directory.

f = new File(path + '\\' + filename);//path and filename are user specified.
FileOutputStream foutput = new FileOutputStream(f);
ObjectOutputStream output = new ObjectOutputStream(foutput);
output.writeObject(result);//result is a File
output.flush();
output.close();

Any time I run this code, it writes a new file with the appropriate name, but the text file I am testing ends up just containing gibberish. Is there any way to convert the File object to a file in the appropriate directory?

EDIT: As it turns out, I was misunderstanding what, exactly, a file is. I have not been transferring the data, but rather the path. How do I transfer an actual file?

"now have a file object which I cannot figure out how to save to a user specified directory" .. Are you asking "How do I copy a file?" ? — Boann
– Boann, Commented Apr 18, 2015 at 4:14
I suspect you are misunderstanding what File and ObjectOutputStream do. Reread the documentation. — Misha
– Misha, Commented Apr 18, 2015 at 4:25
Using Serialization like you do is writing a binary file that represents the object - human cannot "read" it. It sounds like what you're looking for is a JSON/XML representation of your object which could be written to a file - so that a human can read it. Lookup "marshalling and unmarshalling objects in java" — Nir Alfasi
– Nir Alfasi, Commented Apr 18, 2015 at 4:29
Did you transfer a File object, or the bytes the file contains? — Brendan Long
– Brendan Long, Commented Apr 18, 2015 at 5:14
I converted the file to a series of byte arrays and sent them. I reassembled the byte arrays and converted it back to a File object using a custom class I found called ByteUtils. — Schizoreindeer
– Schizoreindeer, Commented Apr 18, 2015 at 16:17

Bruce Lee · Accepted Answer · 2015-04-18 05:08:31Z

3

ObjectOutputStream is a class that outputs a specific format of data to a text file. Only ObjectInputStream's readObject() can decoding that text file. If you open the text file , it is just gibberish ,as you have seen.

you want this:

FileOutputStream fos = new FileOutputStream(path + '\\' + filename);
FileInputStream fis = new FileInputStream(result);
byte[] buf = new byte[1024];    
int hasRead = 0;
while((hasRead = fis.read(buf)) > 0){
    fos.write(buf, 0, hasRead);
}
fis.close();
fos.close();

answered Apr 18, 2015 at 5:08

Bruce Lee

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Marc · Accepted Answer · 2019-01-22 08:58:12Z

1

If I understand your question, how about using a FileWriter?

File result = new File("result.txt");
result.createNewFile();
FileWriter writer = new FileWriter(result); 
writer.write("Hello user3821496\n"); //just an example how you can write a String to it
writer.flush();
writer.close();

edited Jan 22, 2019 at 8:58

Marc

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answered Apr 18, 2015 at 4:29

riddle_me_this

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2 Comments

Schizoreindeer Over a year ago

I have to be able to transfer a file of any type. This only works with text files, correct?

riddle_me_this Over a year ago

That requirement was not clear from your question, but from the API: "FileWriter is meant for writing streams of characters. For writing streams of raw bytes, consider using a FileOutputStream." docs.oracle.com/javase/7/docs/api/java/io/FileWriter.html

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