RabbitMQ--Hello world！（一）

Introduction

RabbitMQ is a message broker. The principal idea is pretty simple: it accepts and forwards messages. You can think about it as a post office: when you send mail to the post box you're pretty sure that Mr. Postman will eventually deliver the mail to your recipient. Using this metaphor RabbitMQ is a post box, a post office and a postman.

RabbitMQ和通常意义上的消息发送，用下面行话：

• Producing means nothing more than sending. A program that sends messages is a producer. We'll draw it like that, with "P":

  

• A queue is the name for a mailbox. It lives inside RabbitMQ. Although messages flow through RabbitMQ and your applications, they can be stored only inside a queue. A queue is not bound by any limits, it can store as many messages as you like ‒ it's essentially an infinite buffer. Many producers can send messages that go to one queue, many consumers can try to receive data from one queue. A queue will be drawn as like that, with its name above it:

  

• Consuming has a similar meaning to receiving. A consumer is a program that mostly waits to receive messages. On our drawings it's shown with "C":

   

helloworld例子

生产者发送消息到队列，消费者取出消息并打印。

send.py

#!/usr/bin/env python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()  

channel.queue_declare(queue='hello')

channel.basic_publish(exchange='',
                      routing_key='hello',
                      body='Hello World!')
print(" [x] Sent 'Hello World!'")
connection.close()

receive.py

#!/usr/bin/env python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()

channel.queue_declare(queue='hello')

def callback(ch, method, properties, body):
    print(" [x] Received %r" % body)

channel.basic_consume(callback,
                      queue='hello',
                      no_ack=True)

print(' [*] Waiting for messages. To exit press CTRL+C')
channel.start_consuming()

代码解释：send.py

#!/usr/bin/env python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters(
               'localhost'))
channel = connection.channel()
与rabbitmq server建立连接，

channel.queue_declare(queue='hello')
创建一个queue，我们发送的消息会被放到这个消息队列。如果消息队列不存在，rabbitmq就会丢弃这条消息

channel.basic_publish(exchange='',
                      routing_key='hello',
                      body='Hello World!')
print(" [x] Sent 'Hello World!'")
在rabbitmq中，消息不能直接发送到queue中，通常会经过一个exchange。这里我们使用默认的exchange，用空串标识。
这个exchange是特殊的，它要求我们精确指定这条消息发送到哪个queue。queue的名字需要通过routing_key变量。

connection.close()
在退出程序前我们要关闭这个连接。

代码解释recv.py

#!/usr/bin/env python
import pika

connection = pika.BlockingConnection(pika.ConnectionParameters(
        host='localhost'))
channel = connection.channel()

channel.queue_declare(queue='hello')
首先连接到rabbitmq server，然后要确保queue存在，创建一个queue使勇queue_declare。
我们可以运行这个命令多次，但如果名字相同，仅有一个会被创建。

def callback(ch, method, properties, body):
    print(" [x] Received %r" % body)
从队列中接收消息是比较复杂的，要为queue订阅一个callback函数。当接收到一个消息，callback函数就会被调用。
我们这个回调函数打印消息内容到屏幕上。

channel.basic_consume(callback,
                      queue='hello',
                      no_ack=True)
下一步，告诉rabbitmq特殊的callback函数应该从我们的hello队列接收消息。

print(' [*] Waiting for messages. To exit press CTRL+C')
channel.start_consuming()
最后，开启一个无限的循环等待数据并在必要的时候运行callback函数。

运行结果：

# python send.py
 [x] Sent 'Hello World!'

# python receive.py
 [*] Waiting for messages. To exit press CTRL+C
 [x] Received b'Hello World!'