Java String to InputStream

Table of Contents

1. Overview
2. Convert With Plain Java
3. Convert With Guava
4. Convert With Commons IO
5. Conclusion

1. Overview

In this quick tutorial, we’re going to look at how to convert a standard String to an InputStream using plain Java, Guava, and the Apache Commons IO library.

This article is part of the “Java – Back to Basic” series here on VietMX’s Blog.

2. Convert With Plain Java

Let’s start with a simple example using Java to do the conversion – using an intermediary byte array:

@Test
public void givenUsingPlainJava_whenConvertingStringToInputStream_thenCorrect() 
  throws IOException {
    String initialString = "text";
    InputStream targetStream = new ByteArrayInputStream(initialString.getBytes());
}

Note that the getBytes() method encodes this String using the platform’s default charset so to avoid undesirable behavior you can use getBytes(Charset charset) and control the encoding process.

3. Convert With Guava

Guava doesn’t provide a direct conversion method but does allow us to get a CharSource out of the String and easily convert it to a ByteSource. Then, obtaining the InputStream is easy:

@Test
public void givenUsingGuava_whenConvertingStringToInputStream_thenCorrect() 
  throws IOException {
    String initialString = "text";
    InputStream targetStream = 
      CharSource.wrap(initialString).asByteSource(StandardCharsets.UTF_8).openStream();
}

Note, however, that the asByteSource method is marked as @Beta. This means it can be removed in the future Guava release. We need to keep this in mind.

4. Convert With Commons IO

Finally, the Apache Commons IO library provides an excellent direct solution:

@Test
public void givenUsingCommonsIO_whenConvertingStringToInputStream_thenCorrect() 
  throws IOException {
    String initialString = "text";
    InputStream targetStream = IOUtils.toInputStream(initialString);
}

Finally – do note that we’re leaving the input stream open in these examples – don’t forget to close it when you’re done.