20220530

本例是懒汉模式
负载均衡器类

import java.util.ArrayList;
import java.util.Random;

class LoadBalancer { 
    
    private static LoadBalancer lbInstance = null;
    
    private ArrayList serverList = null;

    public LoadBalancer() {
        serverList = new ArrayList();
    }

    public static LoadBalancer getLbInst() {
        if (lbInstance == null){
            lbInstance = new LoadBalancer();
        }else {
            return lbInstance;
        }
        return lbInstance;
    }

    public void addServer(String server){
        serverList.add(server);
    }

    public void rmServer(String server){
        serverList.remove(server);
    }

    public String getServer(){
        Random rd = new Random();
        int i = rd.nextInt(serverList.size());
        return (String) serverList.get(i);
    }

}

用户类

class Client {
    public static void main(String[] args) {
        LoadBalancer lb1,lb2,lb3,lb4;
        lb1 = LoadBalancer.getLbInst();
        lb2 = LoadBalancer.getLbInst();
        lb3 = LoadBalancer.getLbInst();
        lb4 = LoadBalancer.getLbInst();

        if (lb1 == lb2 && lb2 == lb3 && lb3 == lb4){
            System.out.println("All them are the same LoadBalancer.");
        }

        lb1.addServer("Server 1");
        lb1.addServer("Server 2");
        lb1.addServer("Server 3");
        lb1.addServer("Server 4");

        for (int i = 0; i < 12; i++) {
            String server = lb1.getServer();
            System.out.println("Distribute task to: "+ server);
        }
    }
}