code: public static String encodeFromFile(final String filename) {
  
          java.io.File file = new java.io.File(filename);
          long fileLength = file.length();
  
          java.io.InputStream ins;
          try {
              ins = new java.io.FileInputStream(file);
          } catch (FileNotFoundException e) {
              System.out.println("Error opening file " + filename + e.getMessage());
              return null;
          }
          String encodedData = encodeFromInputStream(ins, fileLength);
          if (encodedData == null) {
              System.err.println("Error encoding from file " + filename);
          }
          return encodedData;
      }
docs: Convenience method for reading a binary file and base64-encoding it.
  
  @param filename
  Filename for reading binary data
  @return base64-encoded string or null if unsuccessful
  @since 2.1