Java Examples - Check whether a port is already in use
Java ExamplesThe following example demonstrates how to detect whether a port is already in use:
Example
import java.net.*;
import java.io.*;
public class Main {
public static void main(String[] args) {
Socket Skt;
String host = "localhost";
if (args.length > 0) {
host = args[0];
}
for (int i = 0; i < 1024; i++) {
try {
System.out.println("Check"+ i);
Skt = new Socket(host, i);
System.out.println("Port" + i + "Already in use");
}
catch (UnknownHostException e) {
System.out.println("Exception occured"+ e);
break;
}
catch (IOException e) {
}
}
}
}
The output of the above code is:
…… 查看 17 查看 18 查看 19 查看 20 查看 21 端口 21 已被使用 查看 22 查看 23 查看 24 ……
You can also specify the host and port:
Main.java file
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;
import java.net.SocketTimeoutException;
public class Main {
public static void main(String[] args) {
//Check local port 80
log(isSocketAliveUitlitybyCrunchify("localhost", 80));
//Check local port 8080
log(isSocketAliveUitlitybyCrunchify("localhost", 8080));
//Check local port 8081
log(isSocketAliveUitlitybyCrunchify("localhost", 8081));
//Check port 80 of example.com
log(isSocketAliveUitlitybyCrunchify("example.com", 80));
//Check port 443 of example.com
log(isSocketAliveUitlitybyCrunchify("example.com", 443));
//Check port 81 of example.com
log(isSocketAliveUitlitybyCrunchify("example.com", 81));
}
/**
* Check the host port
*
* @param hostName
* @param port
* @return boolean - true/false
*/
public static boolean isSocketAliveUitlitybyCrunchify(String hostName, int port) {
boolean isAlive = false;
//Create a socket
SocketAddress socketAddress = new InetSocketAddress(hostName, port);
Socket socket = new Socket();
//Timeout setting, in milliseconds
int timeout = 2000;
log("hostName: " + hostName + ", port: " + port);
try {
socket.connect(socketAddress, timeout);
socket.close();
isAlive = true;
} catch (SocketTimeoutException exception) {
System.out.println("SocketTimeoutException " + hostName + ":" + port + ". " + exception.getMessage());
} catch (IOException exception) {
System.out.println(
"IOException - Unable to connect to " + hostName + ":" + port + ". " + exception.getMessage());
}
return isAlive;
}
private static void log(String string) {
System.out.println(string);
}
private static void log(boolean isAlive) {
System.out.println("Whether it is actually in use:" + isAlive + "\n");
}
}
The output of the above code is:
hostName: localhost, port: 80 IOException - Unable to connect to localhost:80. Connection refused 是否真正在使用: true hostName: localhost, port: 8080 IOException - Unable to connect to localhost:8080. Connection refused 是否真正在使用: false hostName: localhost, port: 8081 IOException - Unable to connect to localhost:8081. Connection refused 是否真正在使用: false hostName: example.com, port: 80 是否真正在使用: true hostName: example.com, port: 443 是否真正在使用: true hostName: example.com, port: 81 SocketTimeoutException example.com:81. connect timed out 是否真正在使用: falseOther Extensions