WeakHashMap的并发使用

WeakHashMap的并发应用
第一步：生成一个全局WeakHashMap变量

private static WeakHashMap<String, Object> lockMap = new WeakHashMap<String, Object>(50);

第二步：从MAP中取对象。如果有就取出，如果没有就新建放到MAP中

 /**  * 得到同步锁，用完丢弃即可  *   * @param key  * @return  */ protected static Object getSynLockObject(String key) {  synchronized (lockMap) {  Object o = lockMap.get(key);  if (o == null) {  o = new Object();  lockMap.put(key, o);  }  return o;  } }

第三步：锁住不同的对象，这样可以对同一对象进行同步。不同对象可以并发

 public boolean processPaymentResult(YeepayResult result) {  long orderSeqId = result.getOrderSeqId();  // 只要这个Key不丢，同步锁就能起作用，所以要显式的引用这个key值  String synLockKey = String.valueOf(orderSeqId);  Object synLock = PayCenter.getSynLockObject(synLockKey);  /**  * 对同一个订单的操作需要进行同步，防止出错  */  synchronized (synLock) {  return synchroProcessPaymentResult(result);  } }

例：并发情况下，对数据进行加1操作，插入数据库

private Map<String, String> lockMap = new WeakHashMap<String,String>(); //confirm every thread get lock object is the same objectprivate String lockPrefix = this.getClass().getName()+"incrementSequenceNum";private int incrementSequenceNum(String sID, String tID, TopicIndexItem cacheTopic){String syn = lockPrefix + sID+tID;String value = lockMap.get(syn);if(value == null){synchronized(lockPrefix){if(lockMap.get(syn)==null){lockMap.put(syn, syn);}}value = lockMap.get(syn);}//syn = syn.intern();int sequenceNum = 0;synchronized(value){sequenceNum = DB.getTopicSequenceNum(sID, tID)+1;DB.incrementTopicSequenceNum(sID, tID);if(cacheTopic!=null){cacheTopic.setMaxSequenceNum(sequenceNum);}}return sequenceNum;}

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