container/modules/groupcom/src/share/org/apache/catalina/tribes/group/AbsoluteOrder.java

package org.apache.catalina.tribes.group;

import org.apache.catalina.tribes.Member;
import java.util.Comparator;
import java.util.Arrays;

/**
 * <p>Title: Membership - Absolute Order</p>
 *
 * <p>Description: A simple, yet agreeable and efficient way of ordering members</p>
 * <p>
 *    Ordering members can serve as a basis for electing a leader or coordinating efforts.<br>
 *    This is stinky simple, it works on the basis of the <code>Member</code> interface
 *    and orders members in the following format:
 * 
 *  <ol>
 *     <li>IP comparison - byte by byte, lower byte higher rank</li>
 *     <li>IPv4 addresses rank higher than IPv6, ie the lesser number of bytes, the higher rank</li>
 *     <li>Port comparison - lower port, higher rank</li>
 *     <li>UniqueId comparison- byte by byte, lower byte higher rank</li>
 *  </ol>
 *     
 * </p>
 *
 * @author Filip Hanik
 * @version 1.0
 * @see org.apache.catalina.tribes.Member
 */
public class AbsoluteOrder {
    public static final AbsoluteComparator comp = new AbsoluteComparator();
    
    protected AbsoluteOrder() {
        super();
    }

    
    
    public static void absoluteOrder(Member[] members) {
        if ( members == null || members.length == 0 ) return;
        Arrays.sort(members,comp);
    }
    
    
    public static class AbsoluteComparator implements Comparator {
        public int compare(Object o1, Object o2) {
            if ( !((o1 instanceof Member) && (o2 instanceof Member)) ) return 0;
            return compareMembers((Member)o1,(Member)o2);
        }
        
        public int compareMembers(Member m1, Member m2) {
            int result = compareIps(m1,m2);
            if ( result == 0 ) result = comparePorts(m1,m2);
            if ( result == 0 ) result = compareIds(m1,m2);
            return result;
        }
        
        public int compareIps(Member m1, Member m2) {
            return compareBytes(m1.getHost(),m2.getHost());
        }
        
        public int comparePorts(Member m1, Member m2) {
            return compareInts(m1.getPort(),m2.getPort());
        }
        
        public int compareIds(Member m1, Member m2) {
            return compareBytes(m1.getUniqueId(),m2.getUniqueId());
        }
        
        protected int compareBytes(byte[] d1, byte[] d2) {
            int result = 0;
            if ( d1.length == d2.length ) {
                for (int i=0; (result==0) && (i<d1.length); i++) {
                    result = compareBytes(d1[i],d2[i]);
                }
            } else if ( d1.length < d2.length) {
                result = -1;
            } else {
                result = 1;
            }
            return result;
        }
        
        protected int compareBytes(byte b1, byte b2) {
            return compareInts((int)b1,(int)b2);
        }
        
        protected int compareInts(int b1, int b2) {
            int result = 0;
            if ( b1 == b2 ) {

            } else if ( b1 < b2) {
                result = -1;
            } else {
                result = 1;
            }
            return result;
        }
    }
    
}