XML前两行
第一行 版本号和编码
第二行 指定dtd约束
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
DTD约束
* >=0
+ >=1
? <=1
//表示最少一个mappe大标签 mapper大标签里有9种子标签
<!ELEMENT mapper (cache-ref | cache | resultMap* | parameterMap* | sql* | insert* | update* | delete* | select* )+>
//表示有且只有一个configuration大标签
<!ELEMENT configuration (properties?, settings?, plugins?, environments?, mappers?)>