做网站语言搜索引擎的四个组成部分及作用

过滤消息

消息过滤包括基于表达式过滤与基于类模式两种过滤模式。其中表达式过滤⼜分为TAG和SQL92模式

TAG模式过滤

发送消息时我们会为每⼀条消息设置TAG标签，同⼀⼤类中的消息放在⼀个主题TOPIC下，但是如果
进⾏分类我们则可以根据TAG进⾏分类，每⼀类消费者可能不是关系某个主题下的所有消息，我们就可
以通过TAG进⾏过滤，订阅关注的某⼀类数据。

FilterByTagProducer.java

package com.example.rocketmq.demo.filter;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.remoting.common.RemotingHelper;//通过TAG 实现 过滤消息
public class FilterByTagProducer {public static void main(String[] args) throws Exception {//Instantiate with a producer group name.DefaultMQProducer producer = newDefaultMQProducer("please_rename_unique_group_name");// Specify name server addresses.producer.setNamesrvAddr("localhost:9876");//Launch the instance.producer.start();String[] tags = {"TAGA","TAGB","TAGC"};for (int i = 0; i < 10; i++) {String tag =   tags[i%tags.length];//每个消息设置一个tag，tag 二级分类Message msg = new Message("TopicTest",tag,("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));SendResult sendResult = producer.send(msg);System.out.printf("%s%n", sendResult);}//Shut down once the producer instance is not longer in use.producer.shutdown();}
}

FilterByTagConsumer.java

package com.example.rocketmq.demo.filter;import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
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.common.message.MessageExt;import java.util.List;public class FilterByTagConsumer {public static void main(String[] args) throws InterruptedException, MQClientException {// Instantiate with specified consumer group name.DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name");// Specify name server addresses.consumer.setNamesrvAddr("localhost:9876");//订阅Topic，只订阅标签为A或B的消息consumer.subscribe("TopicTest", "TAGA || TAGB");// Register callback to execute on arrival of messages fetched from brokers.consumer.registerMessageListener(new MessageListenerConcurrently() {@Overridepublic ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;}});//Launch the consumer instance.consumer.start();System.out.printf("Consumer Started.%n");}
}

SQL表达式过滤

SQL92表达式消息过滤，是通过消息的属性运⾏SQL过滤表达式进⾏条件匹配，消息发送时需要设置⽤户的属性putUserProperty⽅法设置属性。
支持的语法：

1. 数值⽐较, 如 > , >= , < , <= , BETWEEN , = ;
2. 字符⽐较, 如 = , <> , IN ;
3. IS NULL or IS NOT NULL ;
4. 逻辑连接符 AND , OR , NOT ;

支持的类型：

1. 数值型, 如123, 3.1415;
2. 字符型, 如 ‘abc’, 必须⽤单引号;
3. NULL , 特殊常数;
4. 布尔值, TRUE or FALSE ;

FilterBySQLProducer.java

package com.example.rocketmq.demo.filter;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.remoting.common.RemotingHelper;public class FilterBySQLProducer {public static void main(String[] args) throws Exception {//Instantiate with a producer group name.DefaultMQProducer producer = newDefaultMQProducer("please_rename_unique_group_name");// Specify name server addresses.producer.setNamesrvAddr("localhost:9876");producer.start();String[] tags = {"TagA","TagB","TagC","TagD"};for (int i = 0; i < 10; i++) {try {String tag = tags[i % tags.length];//构建消息Message msg = new Message("TopicTest" /* Topic */,tag /* Tag */,("RocketMQ消息测试，消息的TAG="+tag+  ", 属性 age = " + i + ", == " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));//每个消息设置属性为age，age值为0-9msg.putUserProperty("age", i+"");SendResult sendResult = producer.send(msg);System.out.printf("%s%n", sendResult);} catch (Exception e) {e.printStackTrace();
//                Thread.sleep(1000);}}//Shut down once the producer instance is not longer in use.producer.shutdown();}
}

FilterBySQLConsumer.java

package com.example.rocketmq.demo.filter;import org.apache.rocketmq.client.consumer.DefaultMQPushConsumer;
import org.apache.rocketmq.client.consumer.MessageSelector;
import org.apache.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
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.common.message.MessageExt;import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.List;public class FilterBySQLConsumer {public static void main(String[] args) throws InterruptedException, MQClientException {// Instantiate with specified consumer group name.DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name");// Specify name server addresses.consumer.setNamesrvAddr("localhost:9876");//订阅Topicconsumer.subscribe("TopicTest", MessageSelector.bySql("age between 0 and 6"));consumer.registerMessageListener(new MessageListenerConcurrently() {@Overridepublic ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;}});consumer.start();System.out.println("Consumer===启动成功!");}
}

类过滤模式（基于4.2.0版本）

RocketMQ通过定义消息过滤类的接⼝实现消息过滤