Mybatis源码分析-读取非项目中的xml文件-gongstring(野渔)的博客-技术人有正能量

##	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">
<configuration>
    <environments default="development">
        <environment id="development">
            
            <transactionManager type="JDBC"/>
            
            
            <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>
    
    <mappers>
        
        <mapper resource="/mybatis/mapper/demo.xml"/>
        <mapper url="file:///D:/tmp/mybatis/mybatis/mapper/demo.xml"/>
        <mapper url="http://www.gongstring.com/mybatis/demo.xml"/>
    </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);
          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);
          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();
  }
```