您的读取循环不正确.它们应该是一般形式:

Your read loops are incorrect. They should be of the general form:

String line;
while ((line = reader.readLine()) != null) {
    // Do something with `line`
}

目前你正在扔掉每一个奇数行，如果有奇数行，则打印一个空值.

At present you are throwing away every odd line, and printing a null if there is an odd number of lines.