SqlSessionFactoryBuilder解析配置文件过程
/**
* 解析properties标签
*
* @param context
*
* @throws Exception
*/
private void propertiesElement(XNode context) throws Exception {
if (context != null) {
// 1
Properties defaults = context.getChildrenAsProperties();
// 2
String resource = context.getStringAttribute("resource");
// 3
String url = context.getStringAttribute("url");
if (resource != null && url != null) {
// 4
throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");
}
if (resource != null) {
// 5
defaults.putAll(Resources.getResourceAsProperties(resource));
} else if (url != null) {
// 6
defaults.putAll(Resources.getUrlAsProperties(url));
}
// 7
Properties vars = configuration.getVariables();
if (vars != null) {
// 如果variables不为空，则填充到Properties对象中
defaults.putAll(vars);
}
// 8
parser.setVariables(defaults);
// 9
configuration.setVariables(defaults);
// 从这里可以看出，优先级从低到高是： 子标签 -> resource/url -> configuration.variables【这里是new XMLConfigBuilder的时候可以传入的】 ，且最终结果是把Properties塞到了XPathParser以及Configuration中
}
}
1.先解析properties标签是否有property子标签，读取里面的name和value属性并放入到Properties对象中 2.properties标签下的resource属性
3.properties标签下的url属性
4.resource和url不可以同时配置不然不知道哪个优先
5.resource，则解析资源路径的配置到Properties中(此时是先解析的xml中的property子标签 所以会存在properties文件覆盖掉xml中的配置。properties中的配置优先级高)
6.url，则去网络请求，然后读取配置到Properties中
7.首先获取configuration中现有的variables(也是Properties类型) (优先级SqlSessionFactoryBuilder.build(properties)>xml引入的properties>property子标签定义的属性)
8.然后把Properties配置信息塞入到XPathParser中
9.再把Properties配置信息塞入到Configuration的variables中
1.
2.
配置文件
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"./mybatis-3-config.dtd">
<configuration>
<!--引入外部资源 -->
<properties resource="org/apache/ibatis/mytest/db.properties">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</properties>
<typeAliases>
<typeAlias alias="student" type="org.apache.ibatis.mytest.StudentDto"/>
</typeAliases>
<!--设置默认的环境为开发环境 -->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${db.driver}"/>
<property name="url" value="${db.url}"/>
<property name="username" value="${db.username}"/>
<property name="password" value="${db.password}"/>
</dataSource>
</environment>
<environment id="development2">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${db.driver}"/>
<property name="url" value="${db.url2}"/>
<property name="username" value="${db.username}"/>
<property name="password" value="${db.password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<!-- <package name="com.zzz.mybatis.mapper"/> -->
<mapper resource="org/apache/ibatis/mytest/StudentMapper.xml"/>
</mappers>
</configuration>
