Whole text file to a String in Java

Question

apache commons-io has:

String str = FileUtils.readFileToString(file, "utf-8");

But there is no such utility in the standard java classes. If you (for some reason) don't want external libraries, you'd have to reimplement it. Here are some examples, and alternatively, you can see how it is implemented by commons-io or Guava.

Not within the main Java libraries, but you can use Guava:

String data = Files.asCharSource(new File("path.txt"), Charsets.UTF_8).read();

Or to read lines:

List<String> lines = Files.readLines( new File("path.txt"), Charsets.UTF_8 );

Of course I'm sure there are other 3rd party libraries which would make it similarly easy - I'm just most familiar with Guava.

Java 11 adds support for this use-case with Files.readString, sample code:

Files.readString(Path.of("/your/directory/path/file.txt"));

Before Java 11, typical approach with standard libraries would be something like this:

public static String readStream(InputStream is) {
    StringBuilder sb = new StringBuilder(512);
    try {
        Reader r = new InputStreamReader(is, "UTF-8");
        int c = 0;
        while ((c = r.read()) != -1) {
            sb.append((char) c);
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
    return sb.toString();
}

Notes:

• in order to read text from file, use FileInputStream
• if performance is important and you are reading large files, it would be advisable to wrap the stream in BufferedInputStream
• the stream should be closed by the caller

Java 7 improves on this sorry state of affairs with the Files class (not to be confused with Guava's class of the same name), you can get all lines from a file - without external libraries - with:

List<String> fileLines = Files.readAllLines(path, StandardCharsets.UTF_8);

Or into one String:

String contents = new String(Files.readAllBytes(path), StandardCharsets.UTF_8);
// or equivalently:
StandardCharsets.UTF_8.decode(ByteBuffer.wrap(Files.readAllBytes(path)));

If you need something out of the box with a clean JDK this works great. That said, why are you writing Java without Guava?

In Java 8 (no external libraries) you could use streams. This code reads a file and puts all lines separated by ', ' into a String.

try (Stream<String> lines = Files.lines(myPath)) {
    list = lines.collect(Collectors.joining(", "));
} catch (IOException e) {
    LOGGER.error("Failed to load file.", e);
}