response.setBufferSize(16384)不起作用？

Question

如下的代码，response.isCommitted()判断为true，但以我的理解，以及对默认8192 buffersize做的实验（见后两段代码），按理超过16384的输出字才会这样，现在10000个字就这样了，而且我试了下，貌似超过8192就会，就好像response.setBufferSize(16384)没有生效，但调用response.getBufferSize()的确是16384。

response.setBufferSize(16384);
System.out.println("buffer size: " + response.getBufferSize()); // 16384
for (int i = 0; i < 10000; i++) {
    str += "你";
}
if (response.isCommitted()) { // 会进去
    System.out.println("response has committed");
}

默认bufferSize做的实验：

System.out.println("buffer size: " + response.getBufferSize()); // 8192
for (int i = 0; i < 8191; i++) {
    str += "你";
}
if (response.isCommitted()) { // <8192不会进去
    System.out.println("response has committed");
}

System.out.println("buffer size: " + response.getBufferSize()); // 8192
for (int i = 0; i < 8192; i++) {
    str += "你";
}
if (response.isCommitted()) { // >=8192不会进去
    System.out.println("response has committed");