Lucene 6.1.0中存在的field种类如下（后缀是Field）：
下面介绍几个常用的Field类型：
- TextField
A field that is indexed and tokenized, without term vectors. For example this would be used on a 'body' field, that contains the bulk of a document's text. 是一个会自动被索引和分词的字段。一般被用在文章的正文部分。
- StringField
A field that is indexed but not tokenized: the entire String value is indexed as a single token. For example this might be used for a 'country' field or an 'id' field. If you also need to sort on this field, separately add a SortedDocValuesField to your document. StringField会被索引，但是不会被分词，即会被当作一个完整的token处理，一般用在“国家”或者“ID”.
- StoredField
A field whose value is stored so that IndexSearcher.doc(int) and IndexReader.document() will return the field and its value. 也就是一个默认会被存储的Field。
举个例子 （下面是对新闻数据进行索引的过程，数据存储在MySQL数据库中，title列存文章标题，content存正文，url存文章所在的链接，author是文章的作者）
