I'll put one cushion

As I investigated, it turned out that "text files written in Shift-JIS can be read". You can use the text file generated by executing "ipconfig> ip.txt". As a flow

ipconfig > ip.txt 　　　↓ Specify the character code as Shift-JIS and read ip.txt 　　　↓ Search using indexOf () or split () 　　　↓ Delete ip.txt with a face that doesn't eat anything

What a place, such as.

Pit

It should be noted here that the main body side that hits the OS command and the write side that returns the result when hit are parallel processing. If you start reading without waiting for the process on the writing side to finish, the IOException teacher will naturally come.

sample

Main.java

public class Main {
    public static void main(String[] args) {
        System.out.println(new getWiFiIP().get());
    }
}

getWiFiIP.java

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;


public class getWiFiIP {

    private String ip="";

    public String get(){
        return ip;
    }


    public getWiFiIP() {

        try {

            ProcessBuilder pb=new ProcessBuilder("cmd.exe", "/c", "ipconfig",">","ip.txt");

            Process process = pb.start();   //Start the process
            process.waitFor();              //Wait until the export is finished

            ArrayList<String> list=new Text_read("ip.txt").getText(); //Read text file


            int cnt=list.indexOf("Wireless LAN adapter Wi-Fi:");////////////////////////////////////////////////
            for(;;){
                if(list.get(cnt).indexOf("IPv4")==-1){
                    cnt++;
                }else{
                    break;
                }                                 //Wi from the character string group read and acquired-IP address of Fi connection(IPv4)To search for
            }////////////////////////////////////////////////////////////////////////////////////////////////////


            String[] temp=list.get(cnt).split(":"); //"IPv4 address. . . . . . . . . . . .: ×××.×××.×××.Since it is "XXX", divide it
            ip= temp[1];                            //Substitute the acquired IP address

            new File("ip.txt").delete();            //IP.Delete txt

　　　　　　　////////////////////////////////////////////////////The following error handling
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        if(ip.equals(""))ip= "Failed to get";
    }
}

Text_read.java

import java.io.*;
import java.util.ArrayList;

/////////////////////////////////////////////////////////
//Read the entire text file and store it in ArrayList.//
/////////////////////////////////////////////////////////


public class Text_read {

    private ArrayList<String>text=new ArrayList<String>();      //ArrayList for storage

    public Text_read(String path/*File Path*/){

        try {
            BufferedReader br =new BufferedReader(new InputStreamReader(new FileInputStream(path), "Shift_JIS"));
            for(;;){
                text.add(br.readLine());
                if(text.get(text.size()-1)==null){              
                    text.remove(text.size()-1);                 
                    break;
                }
            }
            br.close();
        }catch(IOException e){
            System.out.println("I / O error");
        }
    }

    public ArrayList<String> getText(){
        return text;                                            
    }
    
}

This solved it for the time being, but if anyone knows an easier way, please let me know ...

Thank you @KIchiro. </ font>