Write your own Generic Comparator

Lets implement PropertyComparator a generic utility classs that is used to sort on properties of an object.The property can be specified as a string using the format specified in org.apache.commons.beanutils.PropertyUtils.You need to include Commons BeanUtils in your classpath.

import java.util.Comparator;
import org.apache.commons.beanutils.PropertyUtils;

public class PropertyComparator implements Comparator{
    private String propertyName;
      public PropertyComparator(String property)
    {
       this.propertyName = property;
    }
     public int compare(Object object1, Object object2)
    {
       int result = 0;
     try
       {
          Object property1 = PropertyUtils.getProperty(object1, propertyName);
          Object property2 = PropertyUtils.getProperty(object2, propertyName);
         if (property1 instanceof Comparable)
          {
             result = ((Comparable)property1).compareTo(property2);
          } 
     }catch (Exception e)
       {
          e.printStackTrace(); 
     }
    return result ;
}

Ok now moving on to usage of this class, Say we have a class called Employee
which is defined like:

public class Employee{
   String empId;
   String empName;

   public Employee(String empId,String empName)
   {
      this.empId = empId;
      this.empName = empName;
   }
   public String getEmpId()
   { 
      return empId;
   }

   public void setEmpId(String empId)
   {
      this.empId = empId;
   }

   public String getEmpName()
   {
      return empName;
   }

  public void setEmpName(String name)
  {
      this.empName = name;
  }

  public String toString()
  {
      return "EmpId : "+empId+" EmpName : "+empName;
  }

}

Ok i must tell you that if you dont have getter and setter methods for the properties , this will not work.

Now moving on

public class TestGenericComparator
    {
        public static void main(String args[])
       {
           Employee emp1 = new Employee("1","Zebra");
           Employee emp2 = new Employee("2","Apple");
           List empList  = new ArrayList();
           empList.add(emp1);
           empList.add(emp2);
           ........................
 
           Collections.sort(empList,new PropertyCoparator("empName"));
           for(Employee emp:empList)
           {
               System.out.println(emp.toString());
           }
       }
 }

Well this concept can be similarly extended for multi property comparators.