上篇文章中，我們構建了一個簡單的日誌係統。接下來，我們將豐富它：能夠使用不同的severity來監聽不同等級的log。比如我們希望隻有error的log才保存到磁盤上。

1. Bindings綁定

    上篇文章中我們是這麼做的綁定：

channel.queue_bind(exchange=exchange_name,
                   queue=queue_name)

    綁定其實就是關聯了exchange和queue。或者這麼說：queue對exchagne的內容感興趣，exchange要把它的Message deliver到queue中。

    實際上，綁定可以帶routing_key 這個參數。其實這個參數的名稱和basic_publish 的參數名是相同了。為了避免混淆，我們把它成為binding key。
    使用一個key來創建binding :

channel.queue_bind(exchange=exchange_name,
                   queue=queue_name,
                   routing_key='black')

對於fanout的exchange來說，這個參數是被忽略的。

2. Direct exchange

  Direct exchange的路由算法非常簡單：通過binding key的完全匹配，可以通過下圖來說明。

3. Multiple bindings

  

4. Emitting logs

首先是我們要創建一個direct的exchange：

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

我們將使用log的severity作為routing key，這樣Consumer可以針對不同severity的log進行不同的處理。
publish：

channel.basic_publish(exchange='direct_logs',
                      routing_key=severity,
                      body=message)

我們使用三種severity：'info', 'warning', 'error'.

5. Subscribing

對於queue，我們需要綁定severity：

result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue

for severity in severities:
    channel.queue_bind(exchange='direct_logs',
                       queue=queue_name,
                       routing_key=severity)

6. 最終版本

The code for emit_log_direct.py:

#!/usr/bin/env python
import pika
import sys

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

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

severity = sys.argv[1] if len(sys.argv) > 1 else 'info'
message = ' '.join(sys.argv[2:]) or 'Hello World!'
channel.basic_publish(exchange='direct_logs',
                      routing_key=severity,
                      body=message)
print " [x] Sent %r:%r" % (severity, message)
connection.close()

The code for receive_logs_direct.py:

#!/usr/bin/env python
import pika
import sys

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

channel.exchange_declare(exchange='direct_logs',
                         type='direct')

result = channel.queue_declare(exclusive=True)
queue_name = result.method.queue

severities = sys.argv[1:]
if not severities:
    print >> sys.stderr, "Usage: %s [info] [warning] [error]" % \
                         (sys.argv[0],)
    sys.exit(1)

for severity in severities:
    channel.queue_bind(exchange='direct_logs',
                       queue=queue_name,
                       routing_key=severity)

print ' [*] Waiting for logs. To exit press CTRL+C'

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

channel.basic_consume(callback,
                      queue=queue_name,
                      no_ack=True)

channel.start_consuming()

我們想把warning和error的log記錄到一個文件中：

$ python receive_logs_direct.py warning error > logs_from_rabbit.log

打印所有log到屏幕：

$ python receive_logs_direct.py info warning error
 [*] Waiting for logs. To exit press CTRL+C

尊重原創，轉載請注明出處 anzhsoft: https://blog.csdn.net/anzhsoft/article/details/19630147

參考資料：

1. https://www.rabbitmq.com/tutorials/tutorial-four-python.html