消费消息示例

前提条件

• 已安装SDK。

• 已配置访问域名及凭证。

授权信息

默认仅限阿里云账号使用本接口，RAM用户只有在被授予了相关API操作权限后方可使用。本接口的授权信息如下表所示。

使用说明

• 该接口用于消费者消费队列中的消息，ReceiveMessage操作会将取得的消息状态变成Inactive，Inactive状态的时间长度由Queue属性VisibilityTimeout指定。

• 消费者在VisibilityTimeout时间内消费成功后需要调用DeleteMessage接口删除该消息，否则该消息将会重新变成Active状态，又可被消费者重新消费。

消息体编码选择

示例代码

示例代码下载，请参见ReceiveMessageDemo。

import com.aliyun.mns.client.CloudAccount;
import com.aliyun.mns.client.CloudQueue;
import com.aliyun.mns.client.MNSClient;
import com.aliyun.mns.common.ClientException;
import com.aliyun.mns.common.ServiceException;
import com.aliyun.mns.common.utils.ServiceSettings;
import com.aliyun.mns.model.Message;
import java.util.List;

/**
 * 1. 遵循阿里云规范，env设置ak、sk。
 * 2. ${"user.home"}/.aliyun-mns.properties 文件配置如下：
 *           mns.endpoint=http://xxxxxxx
 *           mns.msgBodyBase64Switch=true/false
 */
public class ReceiveMessageDemo {
    /**
     * 是否做 base64 编码
     */
    private static final Boolean IS_BASE64 = Boolean.valueOf(ServiceSettings.getMNSPropertyValue("msgBodyBase64Switch","false"));

    public static void main(String[] args) {
        String queueName = "cloud-queue-demo";

        // 遵循阿里云规范，env设置ak、sk。
        CloudAccount account = new CloudAccount(ServiceSettings.getMNSAccountEndpoint());
        //this client need only initialize once
        MNSClient client = account.getMNSClient();
        CloudQueue queue = client.getQueueRef(queueName);

        try {
            // 基础: 单次拉取
            singleReceive(queue);

            // 推荐: 使用的 长轮询批量拉取模型
            longPollingBatchReceive(queue);
        } catch (ClientException ce) {
            System.out.println("Something wrong with the network connection between client and MNS service."
                + "Please check your network and DNS availablity.");
            ce.printStackTrace();
        } catch (ServiceException se) {
            if (se.getErrorCode().equals("QueueNotExist")) {
                System.out.println("Queue is not exist.Please create queue before use");
            } else if (se.getErrorCode().equals("TimeExpired")) {
                System.out.println("The request is time expired. Please check your local machine timeclock");
            }
            se.printStackTrace();
        } catch (Exception e) {
            System.out.println("Unknown exception happened!");
            e.printStackTrace();
        }

        client.close();
    }

    private static void longPollingBatchReceive(CloudQueue queue) {
        System.out.println("=============start longPollingBatchReceive=============");

        // 一次性拉取最多xx条消息
        int batchSize = 15;
        // 长轮询时间为 xx s
        int waitSeconds = 15;

        List<Message> messages = queue.batchPopMessage(batchSize, waitSeconds);
        if (messages != null && messages.size() > 0) {

            for (Message message : messages) {
                printMsgAndDelete(queue,message);
            }
        }

        System.out.println("=============end longPollingBatchReceive=============");

    }

    private static void singleReceive(CloudQueue queue) {
        System.out.println("=============start singleReceive=============");

        Message popMsg = queue.popMessage();
        printMsgAndDelete(queue, popMsg);

        System.out.println("=============end singleReceive=============");
    }

    private static void printMsgAndDelete(CloudQueue queue, Message popMsg) {
        if (popMsg != null) {
            System.out.println("message handle: " + popMsg.getReceiptHandle());
            System.out.println("message body: " + (IS_BASE64 ? popMsg.getMessageBody() : popMsg.getMessageBodyAsRawString()));
            System.out.println("message id: " + popMsg.getMessageId());
            System.out.println("message dequeue count:" + popMsg.getDequeueCount());
            //<<to add your special logic.>>

            //remember to  delete message when consume message successfully.
            queue.deleteMessage(popMsg.getReceiptHandle());
            System.out.println("delete message successfully.\n");
        }
    }

}