Question

My program gets as input parameter a String containing a list of IP Addresses. Each IP address is separated by a line break. It can look like this:

10.1.1.1
2.2.2.2
11.1.1.1

it can look like this

10.1.1.1-20
1.1.1.1

but it can looki like this

172.16.12.1-20 /24
10.1.1.1

I want to check every IP address and return two Lists validAddresses, invalidAddresses.

I’ve already wrote a program that deals with the first the simplest type of input, i.e. no IP address ranges and no network masks.

private String[] extractIPAddress(String address){
    String[] temp;
    temp = address.split("\\s+");
    return temp;
}

Then I do

addressList = extractIPAddress(String.valueOf(value));

for (int i=0; i < addressList.length; i++) {
    if (InetAddresses.isInetAddress(addressList[i]) == true) {
        validAddress = validAddress.concat(addressList[i] + '\n');
    } else {
        invalidAddress = invalidAddress.concat(addressList[i] + '\n');
    }
}

Now I’m pondering how to deal with the most complex type of input, esp.

• when the line has a range attached to it 1.1.1.1-10, how to remove the -10 part in order check the main IP address; how to check whether range part -10 would make a valid IP address i.e. 1.1.1.10 and then how to put everything together, so I can return it as a line of the validAddress String, looking the same way as at the beginning, i.e. 1.1.1.1-10

• same question applies to the network mask /24

What elements would this kind of program have? Could you outline it for me?

I thought I would do the following, but I’m not sure if that’s the right way and how to implement some parts:

• if I find a - then cut off the part starting at the position of - until end of line or “/” (how to do that?)
• save that part into the ipRange variable
• if I find / then cut off that part starting at the position of / until the end of the line
• save that part into netMask variable
• copy the content into the tmp_ipRange = ipRange
• remove the - in the tem_ipRange variable
• replace the last octet of the main IP address with tmp_ipRange (how to do that?)
• add the new IP address to the array created by the String.split() (impossible, because you can’t just add something to an array in java? what alternative do I have? so I can’t use split here?)
• loop through the addressList (see above code) and check if the IP address is a valid IP address
• after the validation add ipRange to the main ipAddress if ipRange is not null (how do I find the main ipAddress the ipRange belongs to?)
• after the validation add netMaske to the main ipAddress (and range) if mainAddress is not null (how do I find the main ipAddress the netMask belongs to?)

Answer 1

OK, I wrote the following code to tackle this task. The code is working as expected. Since this is one of my first java programs at all, I was wondering if you see any issues in this code?:

import java.util.*;
import java.lang.System;

import com.google.common.net.InetAddresses;

public class IPCheck{

  public static String[] extractLine(String line){
    String[] temp;
    temp = line.split("\\s+");

    return temp;
  }

  public static boolean hasNetMask(String line){
    boolean result = false;
    if(line.indexOf("/") != -1)
    result = true;

    return result;
  }

  public static boolean hasIPRange(String line){
    boolean result = false;
    if(line.indexOf("-") != -1)
    result = true;

    return result;
  }

  public static String extractNetMask(String line){
    String result = "";
    result = line.substring(line.indexOf("/"));

    return result;
  }

  public static String extractIPRange(String line){
    String result = "";
    result = line.substring(line.indexOf("-"));

    return result;
  }

  public static String chop(String line, String piece){
    String result = "";
    result = line.replace(piece, "");

    return result;
  }

  public static boolean validateIPRange(String ipRange){
    int tmpInt = 0;
    ipRange = chop(ipRange, "-");
    tmpInt = Integer.valueOf(ipRange);
    if(tmpInt > 255)
      return false;
    else
      return true;
  }

  public static void main(String args[]){
    String validIPAddress = "";
    String invalidIPAddress = "";
    String str = "10.1.1.1-300\n192.180.0.1-10/16\n192.168.0.1111";
    String[] addressList;
    String netMask = "";
    String ipRange = "";

    addressList = extractLine(str);
    for(int i=0; i<addressList.length; i++){

    if(hasNetMask(addressList[i]) == true){
      netMask = extractNetMask(addressList[i]);
      addressList[i] = chop(addressList[i], netMask);
    }

    if(hasIPRange(addressList[i]) == true){
      ipRange = extractIPRange(addressList[i]);
      addressList[i] = chop(addressList[i], ipRange);

       if(validateIPRange(ipRange) == false){
        /*if the IPRange is not valid, let's attach the ipRange
        to the current IP-Address to make it invalid*/
        addressList[i] = addressList[i].concat(ipRange);
        System.out.println( addressList[i]);
       }
    }

    if(InetAddresses.isInetAddress(addressList[i]) == true){
      validIPAddress = validIPAddress.concat(addressList[i] + ipRange + netMask);
    } else {
      invalidIPAddress = invalidIPAddress.concat(addressList[i] + ipRange + netMask);
    }
  }
 }
}