guava/src/com/google/common/io/BaseEncoding.java
public final String encode(byte[] bytes, int off, int len) {
    checkPositionIndexes(off, off + len, bytes.length);
    StringBuilder result = new StringBuilder(maxEncodedSize(len));
    try {
      encodeTo(result, bytes, off, len);
    } catch (IOException impossible) {
      throw new AssertionError(impossible);
    }
    return result.toString();
  }
public final String encode(byte[] bytes, int off, int len) {
    checkPositionIndexes(off, off + len, bytes.length);
    StringBuilder result = new StringBuilder(maxEncodedSize(len));
    try {
      encodeTo(result, bytes, off, len);
    } catch (IOException impossible) {
      throw new AssertionError(impossible);
    }
    return result.toString();
  }
Encodes the specified range of the specified byte array, and returns the encoded {@code
String}.