java - 为什么 URL 启动时会出现 "java.net.ConnectException: Connection timed out"异常？

Question

我的代码中出现了 ConnectException: Connection timed out，并且出现了一些频率。我要访问的 URL 已启动。相同的代码适用于某些用户，但不适用于其他用户。似乎一旦一个用户开始得到这个异常，他们就会继续得到这个异常。

这是堆栈跟踪:

java.net.ConnectException: Connection timed out
Caused by: java.net.ConnectException: Connection timed out
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
    at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
    at java.net.Socket.connect(Socket.java:516)
    at java.net.Socket.connect(Socket.java:466)
    at sun.net.NetworkClient.doConnect(NetworkClient.java:157)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:365)
    at sun.net.www.http.HttpClient.openServer(HttpClient.java:477)
    at sun.net.www.http.HttpClient.<init>(HttpClient.java:214)
    at sun.net.www.http.HttpClient.New(HttpClient.java:287)
    at sun.net.www.http.HttpClient.New(HttpClient.java:299)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:796)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:748)
    at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:673)
    at sun.net.www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:840)

这是我的代码片段:

URLConnection urlConnection = null;
OutputStream outputStream = null;
OutputStreamWriter outputStreamWriter = null;
InputStream inputStream = null;

try {
    URL url = new URL(urlBase);
    urlConnection = url.openConnection();
    urlConnection.setDoOutput(true);

    outputStream = urlConnection.getOutputStream(); // exception occurs on this line
    outputStreamWriter = new OutputStreamWriter(outputStream);
    outputStreamWriter.write(urlString);
    outputStreamWriter.flush();
    inputStream = urlConnection.getInputStream();
    String response = IOUtils.toString(inputStream);
    return processResponse(urlString, urlBase, response);
} catch (IOException e) {
    throw new Exception("Error querying url: " + urlString, e);
} finally {
    IoUtil.close(inputStream);
    IoUtil.close(outputStreamWriter);
    IoUtil.close(outputStream);
}

Answer 1

连接超时(假设一个本地网络和多台客户端计算机)通常是由

引起的

b) 网络配置错误或线路过载导致丢包

c) 过多的请求使服务器过载

d) 服务器上同时存在少量可用线程/进程，导致所有线程/进程都被占用。这种情况尤其发生在需要很长时间才能运行并可能与 c) 结合的请求中。

希望这会有所帮助。