How to check if an IP address is from a particular network/netmask in Java?

Question

I need to determine if given IP address is from some special network in order to authenticate automatically.

Answer 1

To check An IP in a subnet, I used isInRange method in SubnetUtils class. But this method have a bug that if your subnet was X, every IP address that lower than X, isInRange return true. For example if your subnet was 10.10.30.0/24 and you want to check 10.10.20.5, this method return true. To deal with this bug I used below code.

public static void main(String[] args){
    String list = "10.10.20.0/24";
    String IP1 = "10.10.20.5";
    String IP2 = "10.10.30.5";
    SubnetUtils  subnet = new SubnetUtils(list);
    SubnetUtils.SubnetInfo subnetInfo = subnet.getInfo();
    if(MyisInRange(subnetInfo , IP1) == true)
       System.out.println("True");
    else 
       System.out.println("False");
    if(MyisInRange(subnetInfo , IP2) == true)
       System.out.println("True");
    else
       System.out.println("False");
}

private boolean MyisInRange(SubnetUtils.SubnetInfo info, String Addr )
{
    int address = info.asInteger( Addr );
    int low = info.asInteger( info.getLowAddress() );
    int high = info.asInteger( info.getHighAddress() );
    return low <= address && address <= high;
}