異步RPC（Remote procedure call）
Server：提供服務(wù)的服務(wù)，即RPC模型中的Server。
Client：調(diào)用服務(wù)的服務(wù)，即RPC模型中的client。
Client發(fā)送消息給服務(wù)端，消息中包含二個(gè)屬性，一個(gè)是reply_to屬性（value是一個(gè)隊(duì)列名，客戶端服務(wù)一直監(jiān)聽這個(gè)隊(duì)列），一個(gè)是correkation_id(本次請(qǐng)求的唯一標(biāo)識(shí)），發(fā)送消息調(diào)用Server服務(wù)之后，服務(wù)端將調(diào)用結(jié)果發(fā)送到reply_to指定的隊(duì)列中。當(dāng)前也會(huì)根據(jù)客戶端得到correlation_id，并指明這次結(jié)果與correlation_id對(duì)應(yīng)。
java client實(shí)現(xiàn)RPC功能
服務(wù)端代碼,監(jiān)聽sms隊(duì)列（客戶端請(qǐng)求消息發(fā)送到的隊(duì)列）：
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import java.util.concurrent.TimeUnit;
public class Consume {
public static void main(String[] args) throws Exception{
ConnectionFactory connectionFactory = new ConnectionFactory();
connectionFactory.setUri("amqp://zhihao.miao:123456@192.168.1.131:5672");
Connection connection = connectionFactory.newConnection();
Channel channel = connection.createChannel();
System.out.println(channel.queueDeclare().getQueue());
channel.basicConsume("sms",true,new SimpleConsumer(channel));
System.out.println("短信服務(wù)已經(jīng)啟動(dòng)");
TimeUnit.SECONDS.sleep(60);
channel.close();
connection.close();
}
}
接收到客戶端的消息之后，調(diào)用服務(wù)接口sendSMS方法，然后得到請(qǐng)求消息中的reply_to和correlation_id屬性，將調(diào)用接口的結(jié)果發(fā)送到reply_to屬性的隊(duì)列中，指定correlation_id屬性。
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import com.zhihao.miao.rpc.server.SendSMSTool;
import java.io.IOException;
public class SimpleConsumer extends DefaultConsumer {
public SimpleConsumer(Channel channel){
super(channel);
}
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
System.out.println("進(jìn)入RPC方法調(diào)用");
String phone =properties.getHeaders().get("phone").toString();
String content = new String(body);
//調(diào)用服務(wù)
boolean result = SendSMSTool.sendSMS(phone,content);
System.out.println("消息處理成功");
String reply = properties.getReplyTo();
String id = properties.getCorrelationId();
AMQP.BasicProperties props = new AMQP.BasicProperties.Builder().correlationId(id).build();
this.getChannel().basicPublish("",reply,props,(result+"").getBytes());
System.out.println("消息回復(fù)成功");
}
}
服務(wù)接口：
public class SendSMSTool {
public static boolean sendSMS(String phone,String content){
System.out.println("發(fā)送短信內(nèi)容：【"+content+"】到手機(jī)號(hào)："+phone);
return phone.length() > 6;
}
}
總結(jié)
RPC Server步驟：
1.創(chuàng)建服務(wù)
2.監(jiān)聽一個(gè)隊(duì)列（sms），監(jiān)聽客戶端發(fā)送的消息
3.收到消息之后，調(diào)用服務(wù)，得到調(diào)用結(jié)果
4.從消息屬性中，獲取reply_to, correlation_id屬性，把調(diào)用結(jié)果發(fā)送給reply_to指定的隊(duì)列中，發(fā)送的消息屬性要帶上reply_to。
5.一次調(diào)用處理成功
客戶端代碼：
消息端先監(jiān)聽一個(gè)隊(duì)列sms.reply，這個(gè)隊(duì)列是客戶端返回結(jié)果的隊(duì)列，然后發(fā)送消息指定請(qǐng)求參數(shù)（參數(shù)頭和參數(shù)內(nèi)容），指定correlationId和replyTo屬性。
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
public class Send {
public static void main(String[] args) throws Exception{
ConnectionFactory connectionFactory = new ConnectionFactory();
connectionFactory.setUri("amqp://zhihao.miao:123456@192.168.1.131:5672");
Connection connection = connectionFactory.newConnection();
Channel channel = connection.createChannel();
String correlationId = UUID.randomUUID().toString();
String replyTo = "sms.reply";
//自動(dòng)刪除屬性為true，當(dāng)connection關(guān)閉后會(huì)自動(dòng)刪除該隊(duì)列
//channel.queueDeclare(replyTo,true,true,true,new HashMap<>());
channel.basicConsume(replyTo,true,new SimpleConsumer(channel));
Map<String,Object> headers = new HashMap<>();
headers.put("phone","15790934342");
AMQP.BasicProperties properties = new AMQP.BasicProperties.Builder().headers(headers).replyTo(replyTo).correlationId(correlationId).deliveryMode(2).
contentEncoding("UTF-8").build();
channel.basicPublish("send","sms",true,properties,"周年慶6折大促銷，只剩三天。詳情登錄****，去了解詳情。".getBytes());
TimeUnit.SECONDS.sleep(20);
channel.close();
connection.close();
}
}
接收到rpc調(diào)用返回接口的處理邏輯，
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import java.io.IOException;
public class SimpleConsumer extends DefaultConsumer {
public SimpleConsumer(Channel channel){
super(channel);
}
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
System.out.println("====收到RPC調(diào)用 回復(fù)了=====");
System.out.println(properties.getCorrelationId()+",短信發(fā)送結(jié)果："+new String(body));
}
}
總結(jié)
RPC Client步驟：
1.監(jiān)聽reply_to對(duì)應(yīng)的隊(duì)列(RPC調(diào)用結(jié)果發(fā)送指定的隊(duì)列）
2.發(fā)送消息，消息屬性需要帶上reply_to，correlation_id屬性
3.服務(wù)端處理完成之后，reply_to對(duì)應(yīng)的隊(duì)列就會(huì)收到異步處理結(jié)果消息
4.收到消息之后，進(jìn)行處理，根據(jù)消息屬性的correlation_id找到對(duì)應(yīng)的請(qǐng)求
5.一次客戶端調(diào)用就完成了。
說一下邏輯：
就是客戶端往一個(gè)隊(duì)列sms發(fā)送消息，服務(wù)端監(jiān)聽這個(gè)隊(duì)列，接收到消息之后服務(wù)端在消息處理方法中調(diào)用服務(wù)，并把調(diào)用的服務(wù)結(jié)果返回給客戶端，怎么返回呢（通過往一個(gè)隊(duì)列里發(fā)送（sms.reply),并把這次調(diào)用的id也返回給客戶端，這個(gè)隊(duì)列名是reply_to屬性，當(dāng)前的返回id是correlation_id,都是在客戶端往sms隊(duì)列發(fā)送消息的時(shí)候帶到服務(wù)端的），服務(wù)端將返回的結(jié)果發(fā)送到指定的隊(duì)列，而客戶端一直在監(jiān)聽這個(gè)隊(duì)列拿到返回值，即完成了一次異步的rpc調(diào)用。
Direct reply-to
Improve performance and simplicity of RPC clients by sending replies direct to a waiting channel.
通過直接將RPC的回復(fù)發(fā)送到等待的Channel中而提供RPC客戶端的性能。
動(dòng)機(jī)（原因）
RPC is a popular pattern to implement with a messaging broker like RabbitMQ. The typical way to do this is for RPC clients to send requests to a long lived server queue. The RPC server(s) read requests from this queue and then send replies to each client using the queue named by the client in the reply-to header.
But where does the client's queue come from? The client can declare a single-use queue for each request-response pair. But this is inefficient; even a transient unmirrored queue can be expensive to create and then delete (compared with the cost of sending a message). This is especially true in a cluster as all cluster nodes need to agree that the queue has been created, even if it is unmirrored.
So alternatively the client can create a long-lived queue for its replies. But this can be fiddly to manage, especially if the client itself is not long-lived.
The direct reply-to feature allows RPC clients to receive replies directly from their RPC server, without going through a reply queue. ("Directly" here still means going through AMQP and the RabbitMQ server; there is no separate network connection between RPC client and RPC server.)
大意就是使用RabbitMQ實(shí)現(xiàn)異步RPC，通常的做法就是客戶端將請(qǐng)求發(fā)送到長(zhǎng)期存在的服務(wù)器隊(duì)列。RPC服務(wù)器讀取接收此隊(duì)列的請(qǐng)求，然后將RPC調(diào)用結(jié)果返回到客戶端在發(fā)送請(qǐng)求時(shí)請(qǐng)求頭中的reply_to屬性中的隊(duì)列。完成一次異步的RPC調(diào)用。
那么請(qǐng)求頭中的隊(duì)列哪里來呢？客戶端可以聲明一個(gè)針對(duì)每一對(duì)請(qǐng)求的臨時(shí)隊(duì)列。但是開銷太大（相比于發(fā)送消息本身），在集群環(huán)境中更是如此。
如果創(chuàng)建一個(gè)長(zhǎng)期的隊(duì)列呢？如果客戶端本身并不是長(zhǎng)期的那么這個(gè)長(zhǎng)期的隊(duì)列就很難管理。
Direct reply-to就是解決這個(gè)問題的，不需要?jiǎng)?chuàng)建這樣一個(gè)回復(fù)的隊(duì)列。
示列
服務(wù)端
服務(wù)啟動(dòng)類，監(jiān)聽sms隊(duì)列
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import java.util.concurrent.TimeUnit;
public class Consume {
public static void main(String[] args) throws Exception{
ConnectionFactory connectionFactory = new ConnectionFactory();
connectionFactory.setUri("amqp://zhihao.miao:123456@192.168.1.131:5672");
Connection connection = connectionFactory.newConnection();
Channel channel = connection.createChannel();
System.out.println(channel.queueDeclare().getQueue());
channel.basicConsume("sms",true,new SimpleConsumer(channel));
System.out.println("短信服務(wù)已經(jīng)啟動(dòng)");
TimeUnit.SECONDS.sleep(60);
channel.close();
connection.close();
}
}
服務(wù)端監(jiān)聽消息處理器，接收到請(qǐng)求參數(shù)，調(diào)用服務(wù)接口，返回參數(shù)
import com.rabbitmq.client.AMQP.BasicProperties;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import java.io.IOException;
public class SimpleConsumer extends DefaultConsumer {
public SimpleConsumer(Channel channel){
super(channel);
}
@Override
public void handleDelivery(String consumerTag, Envelope envelope, BasicProperties properties, byte[] body) throws IOException {
System.out.println("進(jìn)入RPC方法調(diào)用");
String phone =properties.getHeaders().get("phone").toString();
String content = new String(body);
//調(diào)用服務(wù)
boolean result = SendSMSTool.sendSMS(phone,content);
System.out.println("消息處理成功");
String reply = properties.getReplyTo();
String id = properties.getCorrelationId();
BasicProperties props = new BasicProperties.Builder().correlationId(id).build();
this.getChannel().basicPublish("",reply,props,(result+"").getBytes());
System.out.println("消息回復(fù)成功");
}
}
服務(wù)接口
public class SendSMSTool {
public static boolean sendSMS(String phone,String content){
System.out.println("發(fā)送短信內(nèi)容：【"+content+"】到手機(jī)號(hào)："+phone);
return phone.length() > 6;
}
}
客戶端
改變的是客戶端代碼，直接定義replyTo為amq.rabbitmq.reply-to
import com.rabbitmq.client.*;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
public class Send {
public static void main(String[] args) throws Exception{
ConnectionFactory connectionFactory = new ConnectionFactory();
connectionFactory.setUri("amqp://zhihao.miao:123456@192.168.1.131:5672");
Connection connection = connectionFactory.newConnection();
Channel channel = connection.createChannel();
String correlationId = UUID.randomUUID().toString();
String replyTo ="amq.rabbitmq.reply-to";
channel.basicConsume(replyTo,true,new SimpleConsumer(channel));
Map<String,Object> headers = new HashMap<>();
headers.put("phone","15790934342");
AMQP.BasicProperties properties = new AMQP.BasicProperties.Builder().headers(headers).replyTo(replyTo).correlationId(correlationId).deliveryMode(2).
contentEncoding("UTF-8").build();
channel.basicPublish("send","sms",true,properties,"周年慶6折大促銷，只剩三天。詳情登錄****，去了解詳情。".getBytes());
TimeUnit.SECONDS.sleep(20);
channel.close();
connection.close();
}
}
定義消息監(jiān)聽消費(fèi)者
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;
import java.io.IOException;
public class SimpleConsumer extends DefaultConsumer {
public SimpleConsumer(Channel channel){
super(channel);
}
@Override
public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
System.out.println("====收到RPC調(diào)用恢復(fù)了=====");
System.out.println(properties.getCorrelationId()+",短信發(fā)送結(jié)果："+new String(body));
}
}
管控臺(tái)中也不會(huì)創(chuàng)建amq.rabbitmq.reply-to這個(gè)隊(duì)列，而是直接將返回的消息發(fā)到等到的Channel中，提升異步rpc調(diào)用的性能，amq.rabbitmq.reply-to也叫做偽隊(duì)列。
