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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.

Further reading:

Java Scanner

Tutorial and examples on Java Scanner - scan a String, a File or the Console, validate the input, find or skip Patterns.

Read more

Guava – Write to File, Read from File

How to Write to File and Read from a File using the Guava IO support and utilities.

Read more

Java Byte Array to InputStream

How to convert a byte[] to an InputStream using plain Java or Guava.

Read more

2. Convert using Java

We can use the IO package of java to convert a File to different InputStreams.

2.1. FileInputStream

Let’s start with the first and simplest one – 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);
}

2.2. DataInputStream

Let’s look at another one, where we can use DataInputStream to read binary or primitive data from a file:

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

2.3. SequenceInputStream

Finally, let’s also look at how to use SequenceInputStream to concatenate input stream of two files to a single InputStream:

@Test
public final void givenUsingPlainJava_whenConvertingFileToSequenceInputStream_thenCorrect() 
  throws IOException {
      final File initialFile = new File("src/test/resources/sample.txt");
      final File anotherFile = new File("src/test/resources/anothersample.txt");
      final InputStream targetStream = new FileInputStream(initialFile);
      final InputStream anotherTargetStream = new FileInputStream(anotherFile);
    
      InputStream sequenceTargetStream = 
        new SequenceInputStream(targetStream, anotherTargetStream);
}

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

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.

I just announced the new Spring Boot 2 material, coming in REST With Spring:

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алексей боев
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алексей боев

thanks. nice design )

Java Developer
Guest

Thanks it works on my mac somehow the File for current directory does not work on windows.

Grzegorz Piwowarek
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Grzegorz Piwowarek

Hi, can you give more details?