1.JSONObject.getString(key) 当value为null时 sf.json会解析成'null'字符串。fastjson会解析成null对象
2.fastjson 反序列化成数组，空值丢掉了
如https://github.com/alibaba/fastjson/issues/2841
曲线救国一把 将 为空的默认给null填充

,,,{},,{},

/**
*  string字符串遍历填充
**/
public static String ToInitStringNullComplement(String data){
        StringBuffer sb= new StringBuffer();
        char c1 = ',';
        String c2 = "null";
        if(data ==null)
            return sb.toString();
        if(data.length()==0)
            return sb.toString();
        Field field = null;
        try {
            field = String.class.getDeclaredField("value");
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        }
        field.setAccessible(true);
        char[] chars = new char[0];
        try {
            chars = (char[]) field.get(data);
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        for (int i = 0, n = chars.length; i < n; i++){
            boolean flag=true;
            if(i==0&&chars[i]==c1){
                sb.append(c2).append(chars[i]);
                flag=false;
            }
            if(i<chars.length-1&&chars[i]==c1&&chars[i+1]==c1){
                sb.append(chars[i]).append(c2);
                flag=false;
            }

            if(i==chars.length-1&&chars[i]==c1){
                sb.append(chars[i]).append(c2);
                flag=false;
            }

            if(flag){
                sb.append(chars[i]);
            }

        }
        return sb.toString();
    }