HttpExchange.getRemoteAddress（）需要很长时间

Question

我正在创建在Java HttpServer类上运行的服务器，一切正常，但是我注意到对exchange.getRemoteAddress().getAddress().getCanonicalHostName()调用大约需要4000毫秒，但是即使删除getRemoteAddress，读取请求的主体也很快（）。 有谁知道为什么HttpExchange.getRemoteAddress（）需要这么长时间？ 来自服务器的日志：

[pool-1-thread-1 | 13:25:54] Received request from 192.168.0.104 / Obtaining remote address took 4538 ms
[pool-1-thread-1 | 13:25:54] Downloading request body from 192.168.0.104 took 0 ms
[pool-1-thread-1 | 13:25:54] Generating response body from 192.168.0.104 took 6 ms
[pool-1-thread-1 | 13:25:54] Processing lock request from 192.168.0.104

将exchange.getRemoteAddress().getAddress().getCanonicalHostName()替换为硬编码字符串（“测试”）时记录：

[pool-1-thread-1 | 13:28:00] Received request from test / Obtaining remote address took 0 ms
[pool-1-thread-1 | 13:28:00] Downloading request body from test took 1 ms
[pool-1-thread-1 | 13:28:00] Generating response body from test took 7 ms
[pool-1-thread-1 | 13:28:00] Processing lock request from test

编辑：我的失败，没有正确阅读getCanonicalHostName()文档。 它清楚地说

获取此IP地址的标准域名。 尽力而为方法，这意味着我们可能无法根据基础系统配置返回FQDN。

替换为getHostAddress()

Answer 1

这是因为查找给定IP地址的主机名通常会涉及反向DNS查找 ，即网络查询（或一系列查询），这是一项昂贵的操作，并且比使用硬编码的字符串值自然要慢得多。