简单实现负载均衡

```java

package algorithm.loadbalance;

import com.alibaba.fastjson.JSON;

import java.util.*;

/**

• @author Cao Xuan

• @date 2021/3/21 20:04

• @update 2021/5/5 */ public class LoadBalanceDemo {

  private final List serverList = new ArrayList<>();

  /**

  • client -> server */ private final Map<Client, Server> clientServerMap = new HashMap<>();

  /**

  • <—head—tail—>
  • <—light—weight—>
  • <—former—latter–> */ @Deprecated private void sort() { for (int i = serverList.size() - 1; i > 0; i–) { for (int j = i - 1; j > -1; j–) { Server latter = new Server(serverList.get(i)); Server former = new Server(serverList.get(j)); if (latter.getCurrentLoad().size() > former.getCurrentLoad().size()) { serverList.set(i, former); serverList.set(j, latter); } } } System.out.println(“sorting…”); }

  /**

  • <—head—tail—>
  • <—light—weight—>
  • <—former—latter–> */ private void leafShift() { int size = serverList.size(); for (int i = size - 2; i >= 0; i–) { Server latter = new Server(serverList.get(size - 1)); Server former = new Server(serverList.get(i)); if (latter.getCurrentLoad().size() > former.getCurrentLoad().size()) { serverList.set(size - 1, former); serverList.set(i, latter); System.out.println(“leaf shift”); } } }

  private void rightShift(int index) { int size = serverList.size(); for (int i = index + 1; i < size; i++) { Server former = new Server(serverList.get(index)); Server latter = new Server(serverList.get(i)); if (former.getCurrentLoad().size() < latter.getCurrentLoad().size()) { serverList.set(i, former); serverList.set(index, latter); System.out.println(“right shift”); } } }

  public Server addClient(Client client) { if (serverList.size() > 0) { Server server = new Server(serverList.get(serverList.size() - 1)); String serverName = server.getName(); serverList.get(serverList.size() - 1).updateCurrentLoad(client); System.out.println(“Hi,[” + client.getUsername() + “]. Assign [” + serverName + “] to you”); leafShift(); show(); return server; } else { System.err.println(“no server”); return null; } }

  public void removeClient(String clientName) { Server server = clientServerMap.get(new Client(clientName)); int index = serverList.indexOf(server); if (-1 != index) { server.currentLoad.remove(new Client(clientName)); rightShift(index); System.out.println(“remove a client [” + clientName + “]”); } else { System.err.println(“index = -1”); }

   show();
  

  }

  public void addServer(String name) { Server server = new Server(name, new HashSet<>()); if (serverList.contains(server)) { System.err.println(“The server [” + name + “] already exists”); show(); return; } serverList.add(server); System.out.println(“add a server [” + name + “]”); show(); }

  public void removeServer(String serverName) { serverList.remove(new Server(serverName)); System.out.println(“add a server [” + serverName + “]”); show(); }

  private static class Client {

   private String username;
  
   public Client(String username) {
       this.username = username;
   }
  
   public String getUsername() {
       return username;
   }
  
   public void setUsername(String username) {
       this.username = username;
   }
  
   @Override
   public boolean equals(Object obj) {
       if (!(obj instanceof Client)) {
           return false;
       }
       Client client = (Client) obj;
       return this.getUsername().equals(client.getUsername());
   }
  
   @Override
   public int hashCode() {
       return Objects.hash(username);
   }
  
   @Override
   public String toString() {
       return JSON.toJSONString(this);
   }
  

  }

  private static class Server {

   private String name;
  
   private Set<Client> currentLoad;
  
   public Server(String name) {
       this.name = name;
   }
  
   public Server(Server server) {
       this.name = server.name;
       this.currentLoad = server.currentLoad;
   }
  
   public Server(String name, Set<Client> currentLoad) {
       this.name = name;
       this.currentLoad = currentLoad;
   }
  
   public String getName() {
       return name;
   }
  
   public void setName(String name) {
       this.name = name;
   }
  
   public Set<Client> getCurrentLoad() {
       return currentLoad;
   }
  
   public void setCurrentLoad(Set<Client> currentLoad) {
       this.currentLoad = currentLoad;
   }
  
   public void updateCurrentLoad(Client client) {
       this.currentLoad.add(client);
   }
  
   @Override
   public boolean equals(Object obj) {
       if (!(obj instanceof Server)) {
           return false;
       }
       Server server = (Server) obj;
       return this.getName().equals(server.getName());
   }
  
   @Override
   public String toString() {
       return JSON.toJSONString(this);
   }
  

  }

  public static void main(String[] args) {

   LoadBalanceDemo loadBalanceDemo = new LoadBalanceDemo();
  
   System.out.println("---------------USAGE--------------");
   System.out.println("Add a server: [s+${serverName}]");
   System.out.println("Add a client: [c+${clientName}]");
   System.out.println("Remove a server: [s-${serverName}]");
   System.out.println("Remove a client: [c-${clientName}]");
   System.out.println("Show Current Load: [show]");
   System.out.println("---------------USAGE--------------");
  
   while (true) {
       System.out.println("ready");
       System.out.println();
       Scanner scanner = new Scanner(System.in);
       String s = scanner.next();
       if ("show".equals(s)) {
           loadBalanceDemo.show();
       } else if (s.startsWith("c+")) {
           String clientName = s.substring(2);
           Client client = new Client(clientName);
           Server server = loadBalanceDemo.addClient(client);
           loadBalanceDemo.clientServerMap.put(client, server);
       } else if (s.startsWith("s+")) {
           String serverName = s.substring(2);
           loadBalanceDemo.addServer(serverName);
       } else if (s.startsWith("c-")) {
           String clientName = s.substring(2);
           loadBalanceDemo.removeClient(clientName);
       } else if (s.startsWith("s-")) {
           String serverName = s.substring(2);
           loadBalanceDemo.removeServer(serverName);
       } else {
           System.out.println("?");
       }
       System.out.println("----------------------------------");
   }
  

  }

  private void show() { System.out.println(“current load " + serverList); } }