convert-input-stream-to-a-file
Java – Write an InputStream to a File
1. Overview
In this quick tutorial, we’re going to illustrate how to write an InputStream to a File – first using plain Java, then Guava and finally the Apache Commons IO library.
This article is part of the “Java – Back to Basic” tutorial here on Baeldung.
Further reading:
Java – InputStream to Reader
How to convert an InputStream to a Reader using Java, Guava and the Apache Commons IO library.
Java – Convert File to InputStream
How to open an InputStream from a Java File – using plain Java, Guava and the Apache Commons IO library.
Java InputStream to Byte Array and ByteBuffer
How to convert an InputStream to a byte[] using plain Java, Guava or Commons IO.
2. Convert Using Plain Java
@Test
public void whenConvertingToFile_thenCorrect()
throws IOException {
InputStream initialStream = new FileInputStream(
new File("src/main/resources/sample.txt"));
byte[] buffer = new byte[initialStream.available()];
initialStream.read(buffer);
File targetFile = new File("src/main/resources/targetFile.tmp");
OutputStream outStream = new FileOutputStream(targetFile);
outStream.write(buffer);
}Note that in this example, the input stream has known and pre-determined data – such as a file on disk or an in-memory stream. Because of this, we don’t need to do any bounds checking and we can – if memory allows – simply read it and write it in one go.
If the input stream is linked to an ongoing stream of data – for example, an HTTP response coming from an ongoing connection – then reading the entire stream once is not an option. In that case, we need to make sure we keep reading until we reach the end of the stream:
@Test
public void whenConvertingInProgressToFile_thenCorrect()
throws IOException {
InputStream initialStream = new FileInputStream(
new File("src/main/resources/sample.txt"));
File targetFile = new File("src/main/resources/targetFile.tmp");
OutputStream outStream = new FileOutputStream(targetFile);
byte[] buffer = new byte[8 * 1024];
int bytesRead;
while ((bytesRead = initialStream.read(buffer)) != -1) {
outStream.write(buffer, 0, bytesRead);
}
IOUtils.closeQuietly(initialStream);
IOUtils.closeQuietly(outStream);
}Finally, here’s yet another, simple way we can use Java 8 to do the same operation:
@Test
public void whenConvertingAnInProgressInputStreamToFile_thenCorrect2()
throws IOException {
InputStream initialStream = new FileInputStream(
new File("src/main/resources/sample.txt"));
File targetFile = new File("src/main/resources/targetFile.tmp");
java.nio.file.Files.copy(
initialStream,
targetFile.toPath(),
StandardCopyOption.REPLACE_EXISTING);
IOUtils.closeQuietly(initialStream);
}3. Convert Using Guava
@Test
public void whenConvertingInputStreamToFile_thenCorrect3()
throws IOException {
InputStream initialStream = new FileInputStream(
new File("src/main/resources/sample.txt"));
byte[] buffer = new byte[initialStream.available()];
initialStream.read(buffer);
File targetFile = new File("src/main/resources/targetFile.tmp");
Files.write(buffer, targetFile);
}4. Convert Using Commons IO
@Test
public void whenConvertingInputStreamToFile_thenCorrect4()
throws IOException {
InputStream initialStream = FileUtils.openInputStream
(new File("src/main/resources/sample.txt"));
File targetFile = new File("src/main/resources/targetFile.tmp");
FileUtils.copyInputStreamToFile(initialStream, targetFile);
}And there you have it – 3 quick ways of writing the InputStream to a File.
