java - 需要在 NULL stringbuilder 值中设置空格

Question

我有一个字段，我试图通过使用 StringBuilder 将长度设置为 25，然后在该字段中的特定位置使用字符串值填充它。但是，当我打印出该字段中的值时，值如下所示：

 M�����������0��������������

显然我需要从该字段中删除“�”值。任何帮助/方向将不胜感激。

这是我的代码：

String b44 = toRequestIsoMessage.getString(B44_ADD_RESPONSE_DATA.bitId);
    if (b44 == null) {
        // ***** 20130604 MS - Told Ralph since that position 1 is space filled initially in the request to the CORE so that he can modify for the AVS. *****
        String avsValue = " ";
        try {
            StringBuilder revB44Value = new StringBuilder();
            revB44Value.setLength(25);
            revB44Value.insert(0, avsValue);
            if (decision.cidResponse.responseCode != null) {
                revB44Value.insert(1,  decision.cidResponse.responseCode);
            } else {
                revB44Value.insert(1,  " ");
            }
            if (decision.cvvResponse.responseCode != null) {
                revB44Value.insert(13, decision.cvvResponse.responseCode);                  
            } else {
                revB44Value.insert(13, " ");
            }
            String revB44 = revB44Value.toString();
            toRequestIsoMessage.setString(B44_ADD_RESPONSE_DATA.bitId, revB44Value.toString());
        } catch (InternalISOMsgException e) {
            LOGGER.info(FormatData.fullStackTrace(e));
        }
    }