java.net.ConnectException: Connection refused: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:79)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:606)
at java.net.Socket.connect(Socket.java:555)
at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
at sun.net.www.http.HttpClient.New(HttpClient.java:339)
at sun.net.www.http.HttpClient.New(HttpClient.java:357)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1226)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:990)
at com.kangning.web.test.protocol.URLTest.testOpenConnection(URLTest.java:60)
at com.kangning.web.test.protocol.URLTest.main(URLTest.java:92)
解决办法：
java.nect.ConnectionException:Connection refused:connect 是指客户端与服务端连接失败，可能是服务端没有启动，或者服务器端的端口号与客户端的不一致，或者服务器的防火墙拦截了客户端的请求。
我这边是忘记的启动服务端