kafka消息

Messages consist of a variable-length header, a variable-length opaque key byte array and a variable-length opaque value byte array. The format of the header is described in the following section. Leaving the key and value opaque is the right decision: there is a great deal of progress being made on serialization libraries right now, and any particular choice is unlikely to be right for all uses. Needless to say a particular application using Kafka would likely mandate a particular serialization type as part of its usage. The RecordBatch interface is simply an iterator over messages with specialized methods for bulk reading and writing to an NIO Channel.

消息由一个可变长度header，可变长度不透明的key字节数据和不透明的可变长度value字节数组组成。header的格式在下一章节描述。保持不透明的key和value是正确决定：目前在序列化库方面取得了很大进展，任何特定的选择都不会适合所有的场景。不用说使用Kafka的特定应用程序可能需要特定的序列化类型作为其使用的一部分。RecordBatch接口是对用于批量读取和写入NIOChannel通道的专门方法的消息的简化迭代器。