java - 为什么出现 ConnectException : Connection refused: connect is thrown from HttpURLConnection. getResponseCode()？

Question

这个问题已经有答案了:

java.net.ConnectException: Connection refused (18 个回答)

已关闭 4 年前。

为什么是ConnectException: Connection refused: connect从 HttpURLConnection.getResponseCode() 抛出异常？

URL obj = new URL(url);
HttpURLConnection con = (HttpURLConnection) obj.openConnection();
con.setRequestMethod("POST");
con.getResponseCode(); // this line

异常(exception)是:

java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at sun.net.NetworkClient.doConnect(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.parseHTTPHeader(Unknown Source)
at sun.net.www.http.HttpClient.parseHTTP(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.HttpURLConnection.getResponseCode(Unknown Source)
at com.datasoft.cbsdit.CbsditApplication.main(CbsditApplication.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:87)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:50)
at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:51)

Answer 1

远程计算机 URL 不正确或远程服务器已关闭，如果您尝试使用有效的 url 值(例如: https://stackoverflow.com )，则上述代码可以正常工作:)