display error message for dupliacate record in properties file

This is my code. Here if the properties file contain duplicate records(i.e.)more than one entry e.x.001,002,003,001 i want to display the error message "Duplicate Record found" while compile the java file.Please give the correct solution soon.

import java.io.*; import java.util.*; public class Sample2 { String message; public Sample2() {

       }
       public void setMessage()
       {
        Properties props = new Properties();

try {

     props.load(new FileInputStream("message.properties"));


     message = props.getProperty("002");

         System.out.println(message);
        for (Enumeration e = props.propertyNames();
        e.hasMoreElements();) {

} }

  catch(IOException e)
         {

        e.printStackTrace();

        }
 }
public static void main(String[] args)

     {

    Sample2 gr = new Sample2();

    gr.setMessage();

 }

}