public String buildImageId ( ) { // stream messages end with new line, so call trim to remove it final String stream = stream ( ) ; return stream != null && stream . startsWith ( "Successfully built" ) ? stream . substring ( stream . lastIndexOf ( ' ' ) + 1 ) . trim ( ) : null ; }
Checks if the stream field contains a string a like Successfully built 2d6e00052167 and if so returns the image id . Otherwise null is returned . This string is expected when an image is built successfully .