1. Overview

In this quick tutorial, we’re going to show how to convert a File to an InputStream – first using plain Java and then Guava and the Apache Commons IO library.

This article is part of the “Java – Back to Basic” series here on Baeldung.

2. Convert using Java

Let’s start with the simple Java solution – using a FileInputStream:

@Test
public void givenUsingPlainJava_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = new FileInputStream(initialFile);
}

Note that we’re not closing the resulting stream in these examples.

3. Convert using Guava

Next – let’s see the Guava solution, using an intermediary ByteSource:

@Test
public void givenUsingGuava_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = Files.asByteSource(initialFile).openStream();
}

4. Convert using Commons IO

Finally – let’s look at a solution using Apache Commons IO:

@Test
public void givenUsingCommonsIO_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = FileUtils.openInputStream(initialFile);
}

And there you have it – 3 simple and clean solutions for opening a stream from a Java file.

5. Conclusion

In this article, we explored various ways on how to convert a File to InputStream by using different libraries.
The implementation of all these examples and code snippets can be found over on GitHub – this is a Maven-based project, so it should be easy to import and run as it is.