Class LineReader

guava/src/com/google/common/io/LineReader.java:38–85

A class for reading lines of text. Provides the same functionality as {@link java.io.BufferedReader#readLine()} but for all {@link Readable} objects, not just instances of {@link Reader}. @author Chris Nokleberg @since 1.0

 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
public final class LineReader {
  private final Readable readable;
  private final @Nullable Reader reader;
  private final CharBuffer cbuf = createBuffer();
  private final char[] buf = cbuf.array();

  private final Queue<String> lines = new ArrayDeque<>();
  private final LineBuffer lineBuf =
      new LineBuffer() {
        @Override
        protected void handleLine(String line, String end) {
          lines.add(line);
        }
      };

  /** Creates a new instance that will read lines from the given {@code Readable} object. */
  public LineReader(Readable readable) {
    this.readable = checkNotNull(readable);
    this.reader = (readable instanceof Reader) ? (Reader) readable : null;
  }

  /**
   * Reads a line of text. A line is considered to be terminated by any one of a line feed ({@code
   * '\n'}), a carriage return ({@code '\r'}), or a carriage return followed immediately by a
   * linefeed ({@code "\r\n"}).
   *
   * @return a {@code String} containing the contents of the line, not including any
   *     line-termination characters, or {@code null} if the end of the stream has been reached.
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue // to skip a line
  public @Nullable String readLine() throws IOException {
    while (lines.peek() == null) {
      Java8Compatibility.clear(cbuf);
      // The default implementation of Reader#read(CharBuffer) allocates a
      // temporary char[], so we call Reader#read(char[], int, int) instead.
      int read = (reader != null) ? reader.read(buf, 0, buf.length) : readable.read(cbuf);
      if (read == -1) {
        lineBuf.finish();
        break;
      }
      lineBuf.add(buf, 0, read);
    }
    return lines.poll();
  }
}