How to Filter a txt file in java

As input i have a File containing a list of rooms. Each room has the following information: (1 line of the file)

ID;name;phonenumber;PIN e.g.:
1234;A 0.12;1234;123456789 (ID is same as [first] phonenumber)
2345;A 0.12;2345;123456789 (A room can have more than 1 phonenumber - in a new line like in the example)

Now i need a java program which returns a list like this:

Example Input:
1127,A 0.01,1127,1
2476,A 0.01,2476,1
2309,A 0.01,2309,1
2306,A 0.01,2306,1
2706,A 0.01,2706,1
2757,A 0.01,2757,1
Generates Output:
1127,A 0.01,1127,2476,2309,2306,2706,2757,1

ID;name;phonenumber1;...;phonenumberN;PIN

This code (without main function) adds a second phone number to the existing one, if the rooms from 2 lines are the same.

public static String duplicateNumbers(String s, String x) {

    String result = s;
    if(compareString(s, x)) {
         result = result.substring(0, 21)
                 + x.charAt(21) + x.charAt(22) + x.charAt(23) + x.charAt(24) 
                 + result.substring(20); 
    }
    return result;
}

public static boolean compareString(String s, String x) {
    for(int i = 5; i < 10; i++) {
        if(s.charAt(i) != x.charAt(i)) return false;
    }
    return true;
}

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