Java加权负载均衡策略实现过程解析

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.stereotype.Controller;

@Controller
public class IpMapController extends LogBaseController implements Runnable {
  private static Integer pos = 0;

  // 待scp的Ip列表，Key代表Ip，Value代表该Ip的权重
  public static HashMap<String, Integer> serverWeightMap = new HashMap<String, Integer>();

  static {
  	serverWeightMap.put("127.0.0.1", 1);
  	serverWeightMap.put("127.0.0.2", 1);
  	serverWeightMap.put("127.0.0.3", 1);
  	serverWeightMap.put("127.0.0.4", 1);
  }

  public void run() {
  	// 重建一个Map，避免服务器的上下线导致的并发问题
  	Map<String, Integer> serverMap = new HashMap<String, Integer>();
  	serverMap.putAll(serverWeightMap);

  	// 取得Ip地址List
  	Set<String> keySet = serverMap.keySet();
  	Iterator<String> iterator = keySet.iterator();

  	// 根据权重组成iplist
  	List<String> serverList = new ArrayList<String>();
  	while (iterator.hasNext()) {
  		String server = iterator.next();
  		int weight = serverMap.get(server);
  		for (int i = 0; i < weight; i++)
  			serverList.add(server);
  	}

  	String server = null;
  	synchronized (pos) {
  		if (pos >= keySet.size()){
  			pos = 0;
  		}
  			
  		server = serverList.get(pos);
  		System.out.println("server:" + server + ",pos=" + pos);
  		pos++;
  	}
  	
  }

  public static void main(String[] args) {
  	 IpMapController ipRunnable = new IpMapController();

  	for (int i = 0; i <= 10; i++) {
  		System.out.println("t" + i);
  		new Thread(ipRunnable).start();
  	}
  }
}