public static String toString(URI uri) throws IOException {
        return toString(uri, Charset.defaultCharset());
    }
Gets the contents at the given URI.

@param uri The URI source.
@return The contents of the URL as a String.
@throws IOException if an I/O exception occurs.
@since 2.1
pay-java-common/src/main/java/com/egzosn/pay/common/util/IOUtils.java