请用Java代码和Rocketmq写一个30分钟的后订单取消的代码

由于您没有提供具体的需求，本回答仅提供一个基本的框架。

首先，需要在Rocketmq中创建一个Topic和一个ConsumerGroup，Topic用于发送订单创建消息，ConsumerGroup用于消费订单创建消息并进行后续处理。

创建Topic和ConsumerGroup的代码如下：

DefaultMQProducer producer = new DefaultMQProducer("OrderProducerGroup");
producer.setNamesrvAddr("localhost:9876");
producer.start();

// 创建Topic
MQAdmin admin = new DefaultMQAdminExt();
admin.createTopic("OrderTopic", "OrderTopic", 8);

// 创建ConsumerGroup
DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("OrderConsumerGroup");
consumer.setNamesrvAddr("localhost:9876");
consumer.subscribe("OrderTopic", "*");
consumer.registerMessageListener((MessageListenerConcurrently) (msgs, context) -> {
    for (MessageExt msg : msgs) {
        // 处理订单创建消息
        // TODO
    }
    return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
});
consumer.start();

然后，在订单创建时，向Rocketmq发送一个消息，消息体中包含订单ID和创建时间等信息。发送订单创建消息的代码如下：

Message msg = new Message("OrderTopic", "Order", orderId, ("Order created at " + createTime).getBytes(RemotingHelper.DEFAULT_CHARSET));
SendResult result = producer.send(msg);

在Consumer中接收到订单创建消息后，需要对订单进行处理，例如，将订单的取消时间计算出来并设置一个定时任务，在定时任务到期后自动取消订单。代码如下：

// 计算订单取消时间
long cancelTime = createTime + 30 * 60 * 1000;

// 设置定时任务
Timer timer = new Timer();
timer.schedule(new TimerTask() {
    @Override
    public void run() {
        // 取消订单
        // TODO
    }
}, new Date(cancelTime));

最后，需要在程序退出时关闭Rocketmq的Producer和Consumer。代码如下：

producer.shutdown();
consumer.shutdown();

完整代码如下：

import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
import org.apache.rocketmq.client.consumer.listener.MessageListenerConcurrently;
import org.apache.rocketmq.client.exception.MQClientException;
import org.apache.rocketmq.client.producer.DefaultMQProducer;
import org.apache.rocketmq.client.producer.SendResult;
import org.apache.rocketmq.common.message.Message;
import org.apache.rocketmq.common.message.MessageExt;
import org.apache.rocketmq.remoting.common.RemotingHelper;
import org.apache.rocketmq.tools.admin.DefaultMQAdminExt;
import org.apache.rocketmq.tools.admin.MQAdmin;

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

public class OrderCancellation {

    public static void main(String[] args) throws Exception {
        DefaultMQProducer producer = new DefaultMQProducer("OrderProducerGroup");
        producer.setNamesrvAddr("localhost:9876");
        producer.start();

        // 创建Topic
        MQAdmin admin = new DefaultMQAdminExt();
        admin.createTopic("OrderTopic", "OrderTopic", 8);

        // 创建ConsumerGroup
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("OrderConsumerGroup");
        consumer.setNamesrvAddr("localhost:9876");
        consumer.subscribe("OrderTopic", "*");
        consumer.registerMessageListener((MessageListenerConcurrently) (msgs, context) -> {
            for (MessageExt msg : msgs) {
                // 处理订单创建消息
                String orderId = msg.getKeys();
                String createTime = new String(msg.getBody(), RemotingHelper.DEFAULT_CHARSET);
                System.out.println("Order created: " + orderId + " at " + createTime);

                // 计算订单取消时间
                long cancelTime = Long.parseLong(createTime) + 30 * 60 * 1000;

                // 设置定时任务
                Timer timer = new Timer();
                timer.schedule(new TimerTask() {
                    @Override
                    public void run() {
                        // 取消订单
                        System.out.println("Order cancelled: " + orderId);
                    }
                }, new Date(cancelTime));
            }
            return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
        });
        consumer.start();

        // 发送订单创建消息
        String orderId = "123456";
        long createTime = System.currentTimeMillis();
        Message msg = new Message("OrderTopic", "Order", orderId, String.valueOf(createTime).getBytes(RemotingHelper.DEFAULT_CHARSET));
        SendResult result = producer.send(msg);
        System.out.println("Order created: " + orderId + " at " + createTime);

        // 等待30分钟
        Thread.sleep(30 * 60 * 1000);

        producer.shutdown();
        consumer.shutdown();
    }
}