content: package com.platform.rpc.remoting.invoker.route.impl;
  
  import com.platform.rpc.remoting.invoker.route.XxlRpcLoadBalance;
  
  import java.util.*;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  
  public class XxlRpcLoadBalanceLRUStrategy extends XxlRpcLoadBalance {
  
      private ConcurrentMap<String, LinkedHashMap<String, String>> jobLRUMap = new ConcurrentHashMap<String, LinkedHashMap<String, String>>();
      private long CACHE_VALID_TIME = 0;
  
      public String doRoute(String serviceKey, TreeSet<String> addressSet) {
  
          // cache clear
          if (System.currentTimeMillis() > CACHE_VALID_TIME) {
              jobLRUMap.clear();
              CACHE_VALID_TIME = System.currentTimeMillis() + 1000*60*60*24;
          }
  
          // init lru
          LinkedHashMap<String, String> lruItem = jobLRUMap.get(serviceKey);
          if (lruItem == null) {
              /**
               * LinkedHashMap
               *      a、accessOrder：ture=访问顺序排序（get/put时排序）/ACCESS-LAST；false=插入顺序排期/FIFO；
               *      b、removeEldestEntry：新增元素时将会调用，返回true时会删除最老元素；可封装LinkedHashMap并重写该方法，比如定义最大容量，超出是返回true即可实现固定长度的LRU算法；
               */
              lruItem = new LinkedHashMap<String, String>(16, 0.75f, true){
                  @Override
                  protected boolean removeEldestEntry(Map.Entry<String, String> eldest) {
                      if(super.size() > 1000){
                          return true;
                      }else{
                          return false;
                      }
                  }
              };
              jobLRUMap.putIfAbsent(serviceKey, lruItem);
          }
  
          // put new
          for (String address: addressSet) {
              if (!lruItem.containsKey(address)) {
                  lruItem.put(address, address);
              }
          }
          // remove old
          List<String> delKeys = new ArrayList<>();
          for (String existKey: lruItem.keySet()) {
              if (!addressSet.contains(existKey)) {
                  delKeys.add(existKey);
              }
          }
          if (delKeys.size() > 0) {
              for (String delKey: delKeys) {
                  lruItem.remove(delKey);
              }
          }
  
          // load
          String eldestKey = lruItem.entrySet().iterator().next().getKey();
          String eldestValue = lruItem.get(eldestKey);
          return eldestValue;
      }
  
      @Override
      public String route(String serviceKey, TreeSet<String> addressSet) {
          String finalAddress = doRoute(serviceKey, addressSet);
          return finalAddress;
      }
  
  }
  