ItemReaders and ItemWriters
所有批量处理在最简单的形式上都可以描述为读取大量数据、执行某种类型的计算或转换，然后写出结果。Spring Batch 提供了三个关键接口来帮助执行批量读取和写入：ItemReader、ItemProcessor 和 ItemWriter。
All batch processing can be described in its most simple form as reading in large amounts
of data, performing some type of calculation or transformation, and writing the result
out. Spring Batch provides three key interfaces to help perform bulk reading and writing:
ItemReader, ItemProcessor, and ItemWriter.