前言篇：

为了节约成本，决定通过自研来改造rocketmq，添加任意时间延迟的延时队列，开源版本的rocketmq只有支持18个等级的延迟时间，

其实对于大部分的功能是够用了的，但是以前的项目，全部都是使用了阿里云的rocketmq，原因是不同的供应商的订单的延时时间是不同的

（部分供应商的订单未支付30分钟取消，有些1个半小时取消，各种时间都有），

所以使用了大量的延时队列，但是开源版本不支持任意时间延时（希望官方支持这个功能）

为了实现这个功能，网上查询了不少资料，查询到不少相关的文章，主要实现都是基于时间轮来实现的，

但是比较少开源的代码实现（也许大家都没有这个需求吧）

debug实践篇：

1. 撸起袖子加油干，首先，下载源代码 https://github.com/apache/rocketmq.git，导入ide

运行mvn package 生成jar包，如果成功的话，会生成到distribution目录下面

2. 查看文档，发现要运行namesvr 和 broker

找到 src\main\java\org\apache\rocketmq\namesrv\NamesrvStartup.java ，开心的执行main方法，

哦哦哦哦哦，果然报错了，提示 rocketmq.home.dir 目录不存在，查看源码, 原来是从system.propeties读取的，

为了调试，我毫不犹豫的加上了配置文件，

再次运行，不报错了，控制台显示，成功啦（ 生活是多么美好，空气是多么清晰！ ）

3.运行 broker ，打开 src\main\java\org\apache\rocketmq\broker\BrokerStartup.java，执行main方法，

添加 配置文件 （ D:\\mq\\rocketmq-rocketmq-all-4.9.2是我本地的路径，你要修改成自己的 ）

1 System.setProperty("rocketmq.home.dir", "D:\\mq\\rocketmq-rocketmq-all-4.9.2\\rb");2 System.setProperty("user.home", "D:\\mq\\rocketmq-rocketmq-all-4.9.2\\rb\\home\\");

运行一下，成功了，开心的发一条消息，试试，哦哦哦哦哦。 发不出去哦（ 人生最痛苦的事情是，快要成功了，却没有成功 ） 。

原来还要配置namesvr地址，在启动命令，添加 -n localhost:9876 ( 上面的namesvr 启动的ip和端口)

4.漫长的改造之路 （我们是勇敢的斯巴达勇士，一直勇往直前）

用了阿里云的延时队列，发现它的message 可以传一个时间过来（任意的延时时间）

来来来，我们复制一下（ 不要告诉别人，我们一直是复制，粘贴的，没有原创， 嘘 ...... ）

1/** 2      * 该类预定义一些系统键. 3      */4     static public class SystemPropKey {5         public static final String TAG = "__TAG";6         public static final String KEY = "__KEY";7         public static final String MSGID = "__MSGID";8         public static final String SHARDINGKEY = "__SHARDINGKEY";9         public static final String RECONSUMETIMES = "__RECONSUMETIMES";10         public static final String BORNTIMESTAMP = "__BORNTIMESTAMP";11         public static final String BORNHOST = "__BORNHOST";12/**13          * 设置消息的定时投递时间（绝对时间). 
例1: 延迟投递, 延迟3s投递, 设置为: System.currentTimeMillis() + 3000; 
例2: 定时投递,14          * 2016-02-01 11:30:00投递, 设置为: new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2016-02-0115          * 11:30:00").getTime()16          */17         public static final String STARTDELIVERTIME = "__STARTDELIVERTIME";18     }

/**     * 
 设置消息的定时投递时间（绝对时间),最大延迟时间为7天. 
 
 
延迟投递: 延迟3s投递, 设置为: System.currentTimeMillis() + 3000;
     * 
定时投递: 2016-02-01 11:30:00投递, 设置为: new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2016-02-01     * 11:30:00").getTime()
 
     */    public void setStartDeliverTime(final long value) {        putSystemProperties(SystemPropKey.STARTDELIVERTIME, String.valueOf(value));    }

5.既然要改造rocketmq，在哪里改呢，debug，debug，debug（一直到天荒地老），功夫不负有心人，找到啦，

找到 \src\main\java\org\apache\rocketmq\broker\processor\SendMessageProcessor.java， 发现

public RemotingCommand processRequest(ChannelHandlerContext ctx,                                          RemotingCommand request) throws RemotingCommandException {        SendMessageContext mqtraceContext;switch (request.getCode()) {case RequestCode.CONSUMER_SEND_MSG_BACK:return this.consumerSendMsgBack(ctx, request);default:                SendMessageRequestHeader requestHeader = parseRequestHeader(request);if (requestHeader == null) {return null;                }                mqtraceContext = buildMsgContext(ctx, requestHeader);                this.executeSendMessageHookBefore(ctx, request, mqtraceContext);                RemotingCommand response;if (requestHeader.isBatch()) {                    response = this.sendBatchMessage(ctx, request, mqtraceContext, requestHeader);                } else {                    response = this.sendMessage(ctx, request, mqtraceContext, requestHeader);                }                this.executeSendMessageHookAfter(response, mqtraceContext);return response;        }    }

继续debug，发现 sendMessage 就是处理发送消息的，

如果我们在这里判断是否延时消息就写入文件，然后返回成功到客户端，等到了时间就发送延迟消息，不就搞定了吗？

oh，yes，就是这么干的

//处理延迟消息 delay message        String startTime = msgInner.getProperty(Message.SystemPropKey.STARTDELIVERTIME);        boolean isDelayMsg = false;        long nextStartTime = 0;if (startTime != null && msgInner.getDelayTimeLevel() <= 0) {            nextStartTime = Long.parseLong(startTime);if (nextStartTime >= System.currentTimeMillis()) {                isDelayMsg = true;            }        }if (isDelayMsg) {return delayProcessor.handlePutMessageResultFuture(response, request, msgInner, ctx, queueIdInt, nextStartTime);        } else {if (traFlag != null && Boolean.parseBoolean(traFlag)) {if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {                    response.setCode(ResponseCode.NO_PERMISSION);                    response.setRemark("the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()                                    + "] sending transaction message is forbidden");return response;                }                putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);            } else {                putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);            }return handlePutMessageResult(putMessageResult, response, request, msgInner, responseHeader, sendMessageContext, ctx, queueIdInt);        }    }

其中 delayProcessor.handlePutMessageResultFuture 是我们用来处理延迟消息的地方

我们按照每个时间一个文件夹来保存延时消息，等延时消息到达后，定时的写入延时队列里面。

详细原理，请查考 rocketmq 原理实现篇 https://www.cnblogs.com/tomj2ee/p/15815186.html

package org.apache.rocketmq.broker.delay;import io.netty.channel.ChannelHandlerContext;import org.apache.commons.lang3.time.DateFormatUtils;import org.apache.rocketmq.broker.BrokerController;import org.apache.rocketmq.common.protocol.ResponseCode;import org.apache.rocketmq.common.protocol.header.SendMessageResponseHeader;import org.apache.rocketmq.logging.InternalLogger;import org.apache.rocketmq.logging.InternalLoggerFactory;import org.apache.rocketmq.remoting.protocol.RemotingCommand;import org.apache.rocketmq.store.MessageExtBrokerInner;import java.io.*;import java.net.InetSocketAddress;import java.net.SocketAddress;import java.util.Date;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.ThreadLocalRandom;public class DelayProcessor implements  Runnable {    protected static final InternalLogger log = InternalLoggerFactory.getLogger(DelayProcessor.class.getCanonicalName());    protected final BrokerController brokerController;    protected final SocketAddress storeHost;    private ExecutorService jobTaskExecute = Executors.newFixedThreadPool(16);    public DelayProcessor(final BrokerController brokerController) {        this.brokerController = brokerController;        this.storeHost = new InetSocketAddress(brokerController.getBrokerConfig().getBrokerIP1(), brokerController                .getNettyServerConfig().getListenPort());        Thread thread = new Thread(this);        thread.setName("delayProcessor-run---thread");        thread.setDaemon(true);new File(getDelayPath()).mkdirs();        thread.start();        Thread missCallThread = new Thread(() -> {            try {for(;;) {                    Thread.sleep(10 * 1000);                    sendMissCallMsg();                }            } catch (InterruptedException e) {                e.printStackTrace();            }        });        missCallThread.setName("delayProcessor-callback-thread");        missCallThread.start();        System.out.println("init delay success " +getDelayPath());    }    public RemotingCommand handlePutMessageResultFuture(RemotingCommand response,                                                        RemotingCommand request,                                                        MessageExtBrokerInner msgInner,                                                        ChannelHandlerContext ctx,int queueIdInt, long nextStartTime) {return handlePutMessageResult(response, request, msgInner, ctx, queueIdInt, nextStartTime);    }    private RemotingCommand handlePutMessageResult(RemotingCommand response,                                                   RemotingCommand request, MessageExtBrokerInner msg,                                                   ChannelHandlerContext ctx,int queueIdInt, long nextStartTime) {        boolean svOk = saveMsgFile(nextStartTime, msg);        SendMessageResponseHeader sendMessageResponseHeader = new SendMessageResponseHeader();        sendMessageResponseHeader.setQueueId(1);        sendMessageResponseHeader.setMsgId("0");        sendMessageResponseHeader.setQueueOffset(0l);        sendMessageResponseHeader.setTransactionId("");        RemotingCommand newCommand = RemotingCommand.createRequestCommand(ResponseCode.SUCCESS, sendMessageResponseHeader);if (svOk) {            newCommand.setCode(ResponseCode.SUCCESS);        } else {            newCommand.setCode(ResponseCode.SYSTEM_ERROR);            newCommand.setRemark("发送消息延迟失败！");        }        newCommand.setExtFields(request.getExtFields());        newCommand.setVersion(response.getVersion());        newCommand.setOpaque(response.getOpaque());        newCommand.setLanguage(response.getLanguage());        newCommand.setBody(request.getBody());if (!request.isOnewayRPC()) {            try {                ctx.writeAndFlush(newCommand);            } catch (Throwable e) {                log.error("DelayProcessor process request over, but response failed", e);                log.error(request.toString());                log.error(response.toString());            }        }return newCommand;    }    public void putMessage(MessageExtBrokerInner msgInner) {        this.brokerController.getMessageStore().putMessage(msgInner);    }    @Override    public void run() {for (; ; ) {            long curTime = System.currentTimeMillis() / 1000;            jobTaskExecute.submit(() -> sendMsg(curTime));            try {                Thread.sleep(1000);            } catch (InterruptedException e) {            }        }    }    private String getDelayPath() {        String delayPath = "./delay-store"+ File.separator + "delay";return delayPath;    }    private boolean saveMsgFile(long startTime, MessageExtBrokerInner msgInner) {        ObjectOutputStream objectOutputStream = null;        try {            String msgId =(startTime/1000 )+"-"+ System.currentTimeMillis() + "-" + ThreadLocalRandom.current().nextInt(99999999);            System.out.println( getCurrentTime()+"写入延迟消息 >>" + msgId);            String parentDir = getDelayPath() + File.separator + startTime / 1000;            File parentFile = new File(parentDir);if (!parentFile.exists()) {                parentFile.mkdirs();            }            String fileName = parentDir + File.separator + msgId;            FileOutputStream fos = new FileOutputStream(fileName);            BufferedOutputStream bos = new BufferedOutputStream(fos);            objectOutputStream = new ObjectOutputStream(bos);            objectOutputStream.writeObject(msgInner);returntrue;        } catch (Exception ex) {            log.error("saveMsgFile ex:", ex);returnfalse;        } finally {            try {if (objectOutputStream != null) {                    objectOutputStream.close();                }            } catch (Exception ex) {                log.error("saveMsgFile ex:", ex);            }        }    }    private MessageExtBrokerInner readFile(File f) {        ObjectInputStream ois = null;        try {            ois = new ObjectInputStream(new FileInputStream(f));return (MessageExtBrokerInner) ois.readObject();        } catch (Exception ex) {return null;        } finally {if (ois != null) {                try {                    ois.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }    }    private  void sendMissCallMsg() {        File lst = new File(getDelayPath());        File[] files = lst.listFiles();        long startTime = System.currentTimeMillis() / 1000 - 10 * 1000;for (File f : files) {            String name = f.getName();if (f.isDirectory() && !name.equals(".") && !name.equals("..")) {                try {                    Long fileTime = Long.parseLong(name);if (fileTime <= startTime) {                        sendMsg(fileTime);                    }                } catch (Exception ex) {                }            }        }    }    private String  getCurrentTime(){return  Thread.currentThread().getName()+ ">>["+DateFormatUtils.format(new Date(), "yyyy-MM-dd HH:mm:ss")+"] ";    }    private void sendMsg(long startTime) {        File lst = new File(getDelayPath() + File.separator + startTime);        File[] files = lst.listFiles();if (files != null) {for (File f : files) {                System.out.println( getCurrentTime()+"时间到发送>> "+ startTime+" to commitLog " + f.getName());                MessageExtBrokerInner msgInner = readFile(f);if (msgInner != null) {                    putMessage(msgInner);                    System.out.println( getCurrentTime()+"写入log >> "+ startTime+" to commitLog " + f.getName()+" success");                    f.delete();                }            }            lst.delete();        }    }}

总结：rocketmq延迟队列实现主要是通过时间轮和文件来保存延时消息，等到了时间后，再写入延时队列，来达到延时的目的。

总共有4种方式来实现延时队列，可以参考延时队列的实现原理篇

https://www.cnblogs.com/tomj2ee/p/15815157.html

开源rocketmq延迟队列实现：

https://gitee.com/venus-suite/rocketmq-with-delivery-time.git