使用@TransactionalEventListener监听事务教程

编辑: admin 分类: java 发布时间: 2021-12-03 来源:互联网

@TransactionalEventListener监听事务

项目背景

最近在项目遇到一个问题

A方法体内有 INSERT、UPDATE或者DELETE操作,最后会发送一段MQ给外部，外部接收到MQ后会再发送一段请求过来，系统收到请求后会执行B方法，B方法会依赖A方法修改后的结果，这就有一个问题，如果A方法事务没有提交；且B方法的请求过来了会查询到事务未提交前的状态，这就会有问题

解决办法：@TransactionalEventListener

在Spring4.2+，有一种叫做TransactionEventListener的方式，能够控制在事务的时候Event事件的处理方式。我们知道，Spring的发布订阅模型实际上并不是异步的，而是同步的来将代码进行解耦。而TransactionEventListener仍是通过这种方式，只不过加入了回调的方式来解决，这样就能够在事务进行Commited，Rollback…等的时候才会去进行Event的处理。

具体实现

//创建一个事件类
package com.qk.cas.config;
import org.springframework.context.ApplicationEvent;
public class MyTransactionEvent extends ApplicationEvent {
    private static final long serialVersionUID = 1L;
    private IProcesser processer;
    public MyTransactionEvent(IProcesser processer) {
        super(processer);
        this.processer = processer;
    }
    public IProcesser getProcesser() {
        return this.processer;
    }
    @FunctionalInterface
    public interface IProcesser {
        void handle();
    }
}
//创建一个监听类
package com.qk.cas.config;
import org.springframework.stereotype.Component;
import org.springframework.transaction.event.TransactionPhase;
import org.springframework.transaction.event.TransactionalEventListener;
@Component
public class MyTransactionListener {
    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void hanldeOrderCreatedEvent(MyTransactionEvent event) {
        event.getProcesser().handle();
    }
}
//MQ方法的变动
    @Autowired
    private ApplicationEventPublisher eventPublisher;
    @Autowired
    private AmqpTemplate rabbitTemplate;
    public void sendCreditResult(String applyNo, String jsonString) {
        eventPublisher.publishEvent(new MyTransactionEvent(() -> {
            LOGGER.info("MQ。APPLY_NO:[{}]。KEY:[{}]。通知报文：[{}]", applyNo, Queues.CREDIT_RESULT, jsonString);
            rabbitTemplate.convertAndSend(Queues.CREDIT_RESULT, jsonString);
        }));
    }

拓展

@TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT) 只有当前事务提交之后，才会执行事件监听的方法，其中参数phase默认为AFTER_COMMIT，共有四个枚举：

public enum TransactionPhase {
    /**
     * Fire the event before transaction commit.
     * @see TransactionSynchronization#beforeCommit(boolean)
     */
    BEFORE_COMMIT,
    /**
     * Fire the event after the commit has completed successfully.
     * <p>Note: This is a specialization of {@link #AFTER_COMPLETION} and
     * therefore executes in the same after-completion sequence of events,
     * (and not in {@link TransactionSynchronization#afterCommit()}).
     * @see TransactionSynchronization#afterCompletion(int)
     * @see TransactionSynchronization#STATUS_COMMITTED
     */
    AFTER_COMMIT,
    /**
     * Fire the event if the transaction has rolled back.
     * <p>Note: This is a specialization of {@link #AFTER_COMPLETION} and
     * therefore executes in the same after-completion sequence of events.
     * @see TransactionSynchronization#afterCompletion(int)
     * @see TransactionSynchronization#STATUS_ROLLED_BACK
     */
    AFTER_ROLLBACK,
    /**
     * Fire the event after the transaction has completed.
     * <p>For more fine-grained events, use {@link #AFTER_COMMIT} or
     * {@link #AFTER_ROLLBACK} to intercept transaction commit
     * or rollback, respectively.
     * @see TransactionSynchronization#afterCompletion(int)
     */
    AFTER_COMPLETION
}

注解@TransactionalEventListener

例如用户注册之后需要计算用户的邀请关系，递归操作。如果注册的时候包含多步验证，生成基本初始化数据，这时候我们通过mq发送消息来处理这个邀请关系，会出现一个问题，就是用户还没注册数据还没入库，邀请关系就开始执行，但是查不到数据，导致出错。

@TransactionalEventListener 可以实现事务的监听，可以在提交之后再进行操作。

监听的对象

package com.jinglitong.springshop.interceptor; 
import com.jinglitong.springshop.entity.Customer;
import org.springframework.context.ApplicationEvent;
  
public class RegCustomerEvent extends ApplicationEvent{
    public RegCustomerEvent(Customer customer){
        super(customer);
    }
}

监听到之后的操作

package com.jinglitong.springshop.interceptor; 
import com.alibaba.fastjson.JSON;
import com.jinglitong.springshop.entity.Customer;
import com.jinglitong.springshop.entity.MqMessageRecord;
import com.jinglitong.springshop.servcie.MqMessageRecordService;
import com.jinglitong.springshop.util.AliMQServiceUtil;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import org.springframework.transaction.event.TransactionPhase;
import org.springframework.transaction.event.TransactionalEventListener;  
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
 
@Component
@Slf4j
public class RegCustomerListener {
 
    @Value("${aliyun.mq.order.topic}")
    private String topic;
 
    @Value("${aliyun.mq.regist.product}")
    private String registGroup;
 
    @Value("${aliyun.mq.regist.tag}")
    private String registTag;
 
    @Autowired
    MqMessageRecordService mqMessageRecordService;
 
    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void hanldeRegCustomerEvent(RegCustomerEvent regCustomerEvent) {
        Customer cust = (Customer) regCustomerEvent.getSource();
        Map<String, String> map = new HashMap<String, String>();
        map.put("custId", cust.getZid());
        map.put("account", cust.getAccount());
        log.info("put regist notice to Mq start");
        String hdResult = AliMQServiceUtil.createNewOrder(cust.getZid(), JSON.toJSONString(map),topic,registTag,registGroup);
        MqMessageRecord insert = buidBean(cust.getZid(),hdResult,registTag,JSON.toJSONString(map),registGroup);
        if(StringUtils.isEmpty(hdResult)) {
            insert.setStatus(false);
        }else {
            insert.setStatus(true);
        }
        mqMessageRecordService.insertRecord(insert);
        log.info("put regist notice to Mq end");
        log.info("regist notice userId : " + cust.getAccount());
    }
 
    private MqMessageRecord buidBean (String custId,String result ,String tag,String jsonStr,String groupId) {
        MqMessageRecord msg = new MqMessageRecord();
        msg.setFlowId(custId);
        msg.setGroupName(groupId);
        msg.setTopic(topic);
        msg.setTag(tag);
        msg.setMsgId(result);
        msg.setDataBody(jsonStr);
        msg.setSendType(3);
        msg.setGroupType(1);
        msg.setCreateTime(new Date());
        return msg;
    } 
}
@Autowired
    private ApplicationEventPublisher applicationEventPublisher;
 
applicationEventPublisher.publishEvent(new RegCustomerEvent (XXX));

这样可以确保数据入库之后再进行异步计算

以上为个人经验，希望能给大家一个参考，也希望大家多多支持自由互联。

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