微信公众平台开发时，微信推送消息的机制是推送过来后如果5秒内收不到响应则认为没有推送成功，会再次推送，如果5秒内仍没有收到响应继续推送，总共推送三次。

微信文档原文：

我的解决方案：

1.创建判断重复消息的DuplicateRemovalMessage类；

2.把微信推送的消息解析赋值给DuplicateRemovalMessage对象实例；

3.用静态变量list当缓存，判断DuplicateRemovalMessage实例是否存在于缓存list中，如果存在则为重复消息，如果不存在则不是重复消息并把消息放到缓存list中。

此方案弊端：

1.缓存list会无限增大，所以用setMessageToCache方法限制了list最大容量为1000；

2.解决了list最大容量依然还有弊端，就是两条重复的消息之间如果有超过999个DuplicateRemovalMessage对象依然会判断不准，只能增大list容量来缓解，由于这种情况比较极端，目前远没有那么大业务量，所以暂时这么用着了。

大家有什么好的解决方案一起交流，欢迎拍砖。

下面是具体实现代码：

注意：DuplicateRemovalMessage别忘记复写hashcode、equals方法 

private static final int MESSAGE_CACHE_SIZE = 1000;
	private static List<DuplicateRemovalMessage> MESSAGE_CACHE = new ArrayList<DuplicateRemovalMessage>(MESSAGE_CACHE_SIZE);

	/**
	 * @Description: 判断微信请求是否重复
	 * @return boolean 如果重复返回true
	 */
	public static boolean isDuplicate(Map<String, String> request) {
		String fromUserName = request.get("FromUserName");
		String createTime = request.get("CreateTime");
		String msgId = request.get("MsgId");

		DuplicateRemovalMessage duplicateRemovalMessage = new DuplicateRemovalMessage();

		if (msgId != null) {
			duplicateRemovalMessage.setMsgId(msgId);
		} else {
			duplicateRemovalMessage.setCreateTime(createTime);
			duplicateRemovalMessage.setFromUserName(fromUserName);
		}

		if (MESSAGE_CACHE.contains(duplicateRemovalMessage)) {
			// 缓存中存在，直接pass
			return true;
		} else {
			setMessageToCache(duplicateRemovalMessage);
			return false;
		}
	}
	private static void setMessageToCache(DuplicateRemovalMessage duplicateRemovalMessage) {
		if (MESSAGE_CACHE.size() >= MESSAGE_CACHE_SIZE) {
			MESSAGE_CACHE.remove(0);
		}
		MESSAGE_CACHE.add(duplicateRemovalMessage);
	}

DuplicateRemovalMessage对象：

public class DuplicateRemovalMessage {

	private String MsgId;
	
	private String FromUserName;
	
	private String CreateTime;

	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((CreateTime == null) ? 0 : CreateTime.hashCode());
		result = prime * result + ((FromUserName == null) ? 0 : FromUserName.hashCode());
		result = prime * result + ((MsgId == null) ? 0 : MsgId.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		DuplicateRemovalMessage other = (DuplicateRemovalMessage) obj;
		if (CreateTime == null) {
			if (other.CreateTime != null)
				return false;
		} else if (!CreateTime.equals(other.CreateTime))
			return false;
		if (FromUserName == null) {
			if (other.FromUserName != null)
				return false;
		} else if (!FromUserName.equals(other.FromUserName))
			return false;
		if (MsgId == null) {
			if (other.MsgId != null)
				return false;
		} else if (!MsgId.equals(other.MsgId))
			return false;
		return true;
	}

	
	public String getMsgId() {
		return MsgId;
	}

	public void setMsgId(String msgId) {
		MsgId = msgId;
	}

	public String getFromUserName() {
		return FromUserName;
	}

	public void setFromUserName(String fromUserName) {
		FromUserName = fromUserName;
	}

	public String getCreateTime() {
		return CreateTime;
	}

	public void setCreateTime(String createTime) {
		CreateTime = createTime;
	}
	@Override
	public String toString() {
		StringBuilder builder = new StringBuilder();
		builder.append("DuplicateRemovalMessage [MsgId=");
		builder.append(MsgId);
		builder.append(", FromUserName=");
		builder.append(FromUserName);
		builder.append(", CreateTime=");
		builder.append(CreateTime);
		builder.append("]");
		return builder.toString();
	}

}