How can I write a byte array to a file in Java

Question

How to write a byte array to a file in Java

User · Answer

To write a byte array to a file use the method

public void write(byte[] b) throws IOException

from BufferedOutputStream class.

java.io.BufferedOutputStream implements a buffered output stream. By setting up such an output stream, an application can write bytes to the underlying output stream without necessarily causing a call to the underlying system for each byte written.

For your example you need something like:

String filename= "C:/SO/SOBufferedOutputStreamAnswer";
BufferedOutputStream bos = null;
try {
//create an object of FileOutputStream
FileOutputStream fos = new FileOutputStream(new File(filename));

//create an object of BufferedOutputStream
bos = new BufferedOutputStream(fos);

KeyGenerator kgen = KeyGenerator.getInstance("AES"); 
kgen.init(128); 
SecretKey key = kgen.generateKey(); 
byte[] encoded = key.getEncoded();

bos.write(encoded);

} 
// catch and handle exceptions...

User · Answer

Apache Commons IO Utils has a FileUtils writeByteArrayToFile   method  Note that if you re doing any file IO work then the Apache Commons IO library will do a lot of work for you

User · Answer

File file                byte   data                try              FileOutputStream fos   FileOutputStream file               fos write data               fos flush                fos close              catch Exception e                but if the bytes array length is more than 1024 you should use loop to write the data

User · Answer

No need for external libs to bloat things - especially when working with Android  Here is a native solution that does the trick  This is a pice of code from an app that stores a byte array as an image file          Byte array with image data      final byte   imageData   params 0           Write bytes to tmp file      final File tmpImageFile   new File ApplicationContext getInstance   getCacheDir     scan jpg        FileOutputStream tmpOutputStream   null      try           tmpOutputStream   new FileOutputStream tmpImageFile           tmpOutputStream write imageData           Log d TAG   File successfully written to tmp file              catch  FileNotFoundException e            Log e TAG   FileNotFoundException      e           return null            catch  IOException e            Log e TAG   IOException      e           return null            finally           if tmpOutputStream    null              try                   tmpOutputStream close                  catch  IOException e                    Log e TAG   IOException      e

User · Answer

As of Java 1 7  there s a new way  java nio file Files write  import java nio file Files  import java nio file Paths   KeyGenerator kgen   KeyGenerator getInstance  AES    kgen init 128   SecretKey key   kgen generateKey    byte   encoded   key getEncoded    Files write Paths get  target-file    encoded     Java 1 7 also resolves the embarrassment that Kevin describes  reading a file is now   byte   data   Files readAllBytes Paths get  source-file

User · Answer

As Sebastian Redl points out the most straight forward now java nio file Files write  Details for this can be found in the Reading  Writing  and Creating Files tutorial      Old answer  FileOutputStream write byte     would be the most straight forward  What is the data you want to write   The tutorials for Java IO system may be of some use to you

User · Answer

You can use IOUtils write byte   data  OutputStream output  from Apache Commons IO   KeyGenerator kgen   KeyGenerator getInstance  AES    kgen init 128   SecretKey key   kgen generateKey    byte   encoded   key getEncoded    FileOutputStream output   new FileOutputStream new File  target-file     IOUtils write encoded  output

User · Answer

A commenter asked  why use a third-party library for this   The answer is that it s way too much of a pain to do it yourself   Here s an example of how to properly do the inverse operation of reading a byte array from a file  sorry  this is just the code I had readily available  and it s not like I want the asker to actually paste and use this code anyway    public static byte   toByteArray File file  throws IOException       ByteArrayOutputStream out   new ByteArrayOutputStream        boolean threw   true      InputStream in   new FileInputStream file       try         byte   buf   new byte BUF SIZE         long total   0        while  true            int r   in read buf           if  r    -1             break                   out write buf  0  r                 threw   false        finally         try           in close            catch  IOException e            if  threw              log warn  IOException thrown while closing   e             else            throw e                             return out toByteArray          Everyone ought to be thoroughly appalled by what a pain that is   Use Good Libraries   I  unsurprisingly  recommend Guava s Files write byte    File

[java] How can I write a byte array to a file in Java?

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