How can I write a byte array to a file in Java?
JavaJava Problem Overview
How to write a byte array to a file in Java?
Java Solutions
Solution 1 - Java
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.
Solution 2 - Java
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);
Solution 3 - Java
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"));
Solution 4 - Java
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).
Solution 5 - Java
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...
Solution 6 - Java
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.
Solution 7 - Java
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);
}
}
Solution 8 - Java
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.