今天写代码时，写了下面的代码：
fieldList.stream().filter(xxxx).map(selfDefineMethod())
因为我不需要用stream返回的list，所以后面没有加.collect(Collectors.toList())，结果不及预期，好像这句没有执行一样；后来才发现原因是：
*
* <p>To perform a computation, stream
* <a href="package-summary.html#StreamOps">operations</a> are composed into a
* <em>stream pipeline</em>. A stream pipeline consists of a source (which
* might be an array, a collection, a generator function, an I/O channel,
* etc), zero or more <em>intermediate operations</em> (which transform a
* stream into another stream, such as {@link Stream#filter(Predicate)}), and a
* <em>terminal operation</em> (which produces a result or side-effect, such
* as {@link Stream#count()} or {@link Stream#forEach(Consumer)}).
* Streams are lazy; computation on the source data is only performed when the
* terminal operation is initiated, and source elements are consumed only
* as needed.
*
就是说，stream必须后面加上所谓的terminal operation，类似于count()、forEach()、collect()等操作之后，才会消费原始数据流。
