Mybatis源码分析-读取非项目中的xml文件

mybatis-config.xml配置文件

<?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">
<!--通过这个配置文件，完成mybatis与数据库的连接  -->
<configuration>
<environments default="development">
<environment id="development">
<!-- 配置事务管理 ，采用JDBC管理事务-->
<transactionManager type="JDBC"/>
<!-- POOLED是mybatis的 数据源 -->
<!-- JNDI是基于tomcat的数据源 -->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/demo"/>
<property name="username" value="demo"/>
<property name="password" value="demo"/>
</dataSource>
</environment>
</environments>
<!-- pojo的映射文件UserMapper引入到配入到配置文件中 -->
<mappers>
<!-- resource要写成路径 -->
<mapper resource="/mybatis/mapper/demo.xml"/><!-- 项目中的xml文件 -->
<mapper url="file:///D:/tmp/mybatis/mybatis/mapper/demo.xml"/><!-- 本地磁盘的xml文件 -->
<mapper url="http://www.gongstring.com/mybatis/demo.xml"/><!-- 远程URL的xml文件 -->
</mappers>

</configuration>

demo.xml文件

<?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" >
<mapper namespace="demo" >

<select id="findByPatientNo" resultType="java.util.Map">
select * from base_patient where s_code = #{sCode}
<if test="patientNo != null">
and d_code = #{patientNo}
</if>
</select>

</mapper>

java调用代码

Map<String,Object> params = new HashMap<>();
params.put("sCode","system");
//            params.put("patientNo","111");

String resource = "D:\\tmp\\mybatis\\mybatis\\mybatis-config.xml";
try (InputStream inputStream = new FileInputStream(resource)){
Configuration configuration = new Configuration();

SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
SqlSessionFactory factory = builder.build(inputStream);
datas = factory.openSession().selectList("demo.findBySql",params);
System.out.println(JSON.toJSONString(datas));

}catch (Exception e){
e.printStackTrace();
}

源码分析

在Mybatis的SqlSessionFactory启动时，会先读取mybatis-config.xml配置文件进行初始化。mappers标签里面配置的xml文件，在XMLConfigBuilder.parseConfiguration(XNode root)方法中进行加载，而mybatis底层提供了几种xml加载方式，支持项目中的xml读取，以及URL的方式。

private void parseConfiguration(XNode root) {
try {
propertiesElement(root.evalNode("properties")); //issue #117 read properties first
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
settingsElement(root.evalNode("settings"));
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers")); //加载Mappers中的配置文件
} catch (Exception e) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
}
}

mapperElement方法：

private void mapperElement(XNode parent) throws Exception {
if (parent != null) {
for (XNode child : parent.getChildren()) {
if ("package".equals(child.getName())) {
String mapperPackage = child.getStringAttribute("name");
configuration.addMappers(mapperPackage);
} else {
String resource = child.getStringAttribute("resource");
String url = child.getStringAttribute("url");
String mapperClass = child.getStringAttribute("class");
if (resource != null && url == null && mapperClass == null) {
ErrorContext.instance().resource(resource);
InputStream inputStream = Resources.getResourceAsStream(resource);///////////// 读取本地类路径下面的xml
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url != null && mapperClass == null) {
ErrorContext.instance().resource(url);
InputStream inputStream = Resources.getUrlAsStream(url);///////////// 读取URL资源中的xml
XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments());
mapperParser.parse();
} else if (resource == null && url == null && mapperClass != null) {
Class<?> mapperInterface = Resources.classForName(mapperClass);
configuration.addMapper(mapperInterface);
} else {
throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one.");
}
}
}
}
}

Resources.getUrlAsStream(url)方法：

public static InputStream getUrlAsStream(String urlString) throws IOException {
URL url = new URL(urlString); ////// 说明支持多种文件读取方式
URLConnection conn = url.openConnection();
return conn.getInputStream();
}