Open a file in Java with InputStream.

Given a filename such as this, in the src/main/resources directory:

String filename = "avengers.txt"

The steps to open this file are:

  • Create an InputStream to get this file from the resources directory
  • Create an InputStreamReader to read the stream
  • Create a BufferedReader to read the file
  • Then you can process the data like adding each line to an ArrayList


  • Use the InputStream inside a try/catch with IOException
  • Assert that the InputStream instance is not null.

In this example, DigitFileReader is the current class name:

List<String> textFileData = new ArrayList<>();

try (InputStream inputStream = DigitFileReader.class.getClassLoader().getResourceAsStream(filename)) {
	assert inputStream != null;
	InputStreamReader streamReader = new InputStreamReader(inputStream);
	BufferedReader reader = new BufferedReader(streamReader);

	String line;
	while ((line = reader.readLine()) != null) {
} catch (IOException e) {
	throw new RuntimeException(e);