I am experimenting with websockets
and I want to make it connect to local network automatically from another computer on the LAN
and since there are 255 possible computers on the same network I want it to try all and then connect to whichever it can connect to first. However, first part of an IP address, 192.168.1.* , is different based on router settings.
I can get the whole current IP address of the machine, then I want to extract the front part.
For example
25.0.0.5 will become 25.0.0.
192.168.0.156 will become 192.168.0.
192.168.1.5 will become 192.168.1.
and so on
String Ip = "123.345.67.1";
//what do I do here to get IP == "123.345.67."
You can use a regex for this:
String Ip = "123.345.67.1";
String IpWithNoFinalPart = Ip.replaceAll("(.*\\.)\\d+$", "$1");
System.out.println(IpWithNoFinalPart);
A quick regex explanation: (.*\\\\.)
is a capturing group that holds all characters up to the last .
(due to greedy matching with *
quantifier), \\\\d+
matches 1 or several digits, and $
is the end of string.
Here is a sample program on TutorialsPoint .
String Ip = "123.345.67.1";
String newIp = Ip.replaceAll("\\.\\d+$", "");
System.out.println(newIp);
Output:
123.345.67
Explanation:
\.\d+$
Match the character “.” literally «\.»
Match a single character that is a “digit” «\d+»
Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Assert position at the end of the string, or before the line break at the end of the string, if any «$»
Demo:
Instead of a regex you could make use of String.lastIndexOf('.')
to find the last dot and String.substring(...)
to extract the first part as follows:
String ip = "192.168.1.5";
System.out.println(ip.substring(0, ip.lastIndexOf('.') + 1));
// prints 192.168.1.
Just split the string on the dot "." If the string is a valid IP Address string, then you should then have a String[] array with 4 parts, you can then join only the first 3 with a dot "." and have the "front part"
ie
String IPAddress = "127.0.0.1";
String[] parts = IPAddress.split(".");
StringBuffer frontPart = new StringBuffer();
frontPart.append(parts[0]).append(".")
.append(parts[1]).append(".")
.append(parts[2]).append(".");
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