How to convert InputStream to OutputStream in Java

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 into an OutputStream object.

Convert InputStream to OutputStream using InputStream.transferTo()

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();
}

Convert InputStream to OutputStream using manual 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();
}

Convert InputStream to OutputStream using Apache Commons IO

The Apache Commons IO library provides the 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.gradle file:

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

Further Reading

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

• Reading and Writing Files in Java
• How to Read and Write Text Files in Java
• How to Read and Write Binary Files in Java
• Reading and Writing Files using Java NIO API
• How to read a file line by line in Java

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