FULL PRODUCT VERSION :
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)


A DESCRIPTION OF THE PROBLEM :
If Base64.getMimeEncoder(lineLength, lineSeparator) is called with a lineLength value between 1-3 the resulting encoder is incorrectly initialized leading to different behavior between methods wrap and encodeXXX: Sequences encoded through the OutputStream from the wrap method contain a leading line separator.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The encoded result from the wrap method should not contain a leading line separator.
ACTUAL -
Leading line separator

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Base64;

public class Base64Bug {

  public static void main(String[] args) throws IOException {
    String input = "Man";
    int lineLength = 1; // values 1-3 will cause this error. Line 138 of Base64 should probably be 'if (lineLength / 4 <= 0) {'
    Base64.Encoder encoder = Base64.getMimeEncoder(lineLength, new byte[]{'@'});

    ByteArrayOutputStream result = new ByteArrayOutputStream();
    OutputStream out = encoder.wrap(result);

    out.write(input.getBytes());
    out.close();
    System.out.println(new String(result.toByteArray())); // @TWFu <- line separator at beginning of output
    System.out.println(new String(encoder.encode(input.getBytes()))); // TWFu
  }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Initialize the encoder with a line length value of 0 or >=4