Android Socket communication errors: ECONNREFUSED (Connection refused)

1, by the following code, the client socket socket connection when the server:

Socket socket = new Socket(serverIp, Constant.PORT);

The following exception occurs:

java.net.ConnectException: failed to connect to /192.168.43.203 (port 54321) from /:: (port 39516): connect failed: ECONNREFUSED (Connection refused)
    at libcore.io.IoBridge.connect(IoBridge.java:143)
    at java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:142)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:390)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:230)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:212)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:436)
    at java.net.Socket.connect(Socket.java:621)
    at java.net.Socket.connect(Socket.java:570)
    at java.net.Socket.<init>(Socket.java:450)
    at java.net.Socket.<init>(Socket.java:218)
    at com.sswl.tool.fragment.WifiClientFragment$5.run(WifiClientFragment.java:87)
    at java.lang.Thread.run(Thread.java:919)
Caused by: android.system.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
    at libcore.io.Linux.connect(Native Method)
    at libcore.io.ForwardingOs.connect(ForwardingOs.java:95)
    at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:136)
    at libcore.io.ForwardingOs.connect(ForwardingOs.java:95)
    at libcore.io.IoBridge.connectErrno(IoBridge.java:157)
    at libcore.io.IoBridge.connect(IoBridge.java:135)
	... 11 more

2, the abnormality cause, mainly because 客户端socket所请求的服务端ip与端口并没有开启监听线程, the main direction of the investigation are the following:

• Ip is possible that the port corresponding to the server 监听线程没有成功开启or has crashed;
• The client socket connection 服务端ip或者端口有误;
• The client resolves to use the socket 错误IP的DNS名称connection;
• There may be server-side 防火墙给屏蔽, but this possibility is relatively low