public final String numberString() {
        int offset = np;
        if (offset == -1) {
            offset = 0;
        }
        char chLocal = charAt(offset + sp - 1);

        int sp = this.sp;
        if (chLocal == 'L' || chLocal == 'S' || chLocal == 'B' || chLocal == 'F' || chLocal == 'D') {
            sp--;
        }

        String value = new String(buf, offset, sp);
        return value;
    }
The value of a literal token, recorded as a string. For integers, leading 0x and 'l' suffixes are suppressed.
src/main/java/com/alibaba/fastjson/parser/JSONReaderScanner.java