In my previous article, we looked at different ways to convert an InputStream instance to a file using Java. In this article, you'll learn how to transform an InputStream object to an OutputStream object.

Using InputStream.transferTo() Method

In Java 9 or higher, you can use the InputStream.transferTo() method to copy data from InputStream to OutputStream. This method reads all bytes from this input stream and writes the bytes to the given output stream in the original order.

Here is an example:

try (InputStream in = Files.newInputStream(Paths.get("input.txt"));
     OutputStream out = Files.newOutputStream(Paths.get("output.txt"))) {

    // convert input stream to output stream
    long length = in.transferTo(out);

    System.out.println("Bytes transferred: " + length);

} catch (IOException ex) {
    ex.printStackTrace();
}

Manually Copy Data

In Java 8 or below, you can manually copy data from an InputStream to an OutputStream object as shown below:

try (InputStream in = Files.newInputStream(Paths.get("input.txt"));
     OutputStream out = Files.newOutputStream(Paths.get("output.txt"))) {

    int length;
    byte[] bytes = new byte[1024];

    // copy data from input stream to output stream
    while ((length = in.read(bytes)) != -1) {
        out.write(bytes, 0, length);
    }

} catch (IOException ex) {
    ex.printStackTrace();
}

Using Apache Commons IO

The Apache Commons IO library provides IOUtils.copy() method to copy data from InputStream to an OutputStream as shown below:

try (InputStream in = Files.newInputStream(Paths.get("input.txt"));
     OutputStream out = Files.newOutputStream(Paths.get("output.txt"))) {

    // convert input stream to output stream
    int bytesCopied = IOUtils.copy(in, out);

    System.out.println("Bytes Copied: " + bytesCopied);
} catch (IOException ex) {
    ex.printStackTrace();
}

Don't forget to include Apache Commons IO dependency to your Maven's project pom.xml file:

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>

For a Gradle project, add the following dependency to your build.gralde file:

implementation 'commons-io:commons-io:2.6'

Further Reading

You may be interested in other Java I/O articles:

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