1. In Camel, there are two abstractions for modeling messages, both of which we’ll cover 
    2. in this section.
    3. ■ org.apache.camel.Message—The fundamental entity containing the data 
    4. being carried and routed in Camel
    5. ■ org.apache.camel.Exchange—The Camel abstraction for an exchange of messages. This exchange of messages has an “in” message and as a reply, an “out” 
    6. message
    7. We’ll start by looking at Message to understand how data is modeled and carried in 
    8. Camel. Then we’ll look at how a “conversation” is modeled in Camel by the Exchange.

    在Camel中，有两种用于建模消息的抽象，我们将介绍这两种抽象
    在本节中。
    ■ org.apache.camel.Message.消息包含数据的基本实体
    ■ org.apache.camel.Exchange. Camel用来交换数据的抽象。此消息交换有一个“in”消息，作为答复，还有一个“out”消息
    我们将从查看消息开始，以了解数据是如何建模和携带进来的。然后，我们将看看交换如何在Camel中对“对话”进行建模。