// mybatis初始化
String resource = "mybatis-config.xml"; 
InputStream inputStream = Resources.getResourceAsStream(resource); 
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
// 创建SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession(); 
// 执行SQL语句
List list = sqlSession.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo");

public SqlSessionFactory build(InputStream inputStream) { 
 return build(inputStream, null, null); 
} 
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { 
 try { 
 //2. 创建XMLConfigBuilder对象用来解析XML配置文件，生成Configuration对象 
 XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); 
 //3. 将XML配置文件内的信息解析成Java对象Configuration对象 
 Configuration config = parser.parse(); 
 //4. 根据Configuration对象创建出SqlSessionFactory对象 
 return build(config); 
 } catch (Exception e) { 
 throw ExceptionFactory.wrapException("Error building SqlSession.", e); 
 } finally { 
 ErrorContext.instance().reset(); 
 try { 
 inputStream.close(); 
 } catch (IOException e) { 
 // Intentionally ignore. Prefer previous error.  
 } 
 }
}
// 从此处可以看出，MyBatis内部通过Configuration对象来创建SqlSessionFactory,用户也可以自己通过API构造好Configuration对象，调用此方法创SqlSessionFactory 
public SqlSessionFactory build(Configuration config) { 
 return new DefaultSqlSessionFactory(config); 
} 

public Configuration parse() { 
 if (parsed) { 
 throw new BuilderException("Each XMLConfigBuilder can only be used once."); 
 } 
    parsed = true; 
 //源码中没有这一句，只有 parseConfiguration(parser.evalNode("/configuration"));  
 //为了让读者看得更明晰，源码拆分为以下两句 
 XNode configurationNode = parser.evalNode("/configuration"); 
 parseConfiguration(configurationNode); 
 return configuration; 
} 
/** 
 * 解析 "/configuration"节点下的子节点信息，然后将解析的结果设置到Configuration对象中 
 */ 
private void parseConfiguration(XNode root) { 
 try { 
 //1.首先处理properties 节点 
 propertiesElement(root.evalNode("properties")); //issue #117 read properties first  
 //2.处理typeAliases 
 typeAliasesElement(root.evalNode("typeAliases")); 
 //3.处理插件 
 pluginElement(root.evalNode("plugins")); 
 //4.处理objectFactory 
 objectFactoryElement(root.evalNode("objectFactory")); 
 //5.objectWrapperFactory 
 objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); 
 //6.settings  
 settingsElement(root.evalNode("settings")); 
 //7.处理environments  
 environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631  
 //8.database 
 databaseIdProviderElement(root.evalNode("databaseIdProvider")); 
 //9.typeHandlers 
 typeHandlerElement(root.evalNode("typeHandlers")); 
 //10.mappers 
 mapperElement(root.evalNode("mappers")); 
 } catch (Exception e) { 
 throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); 
 } 
} 

/** 
 * 解析environments节点，并将结果设置到Configuration对象中 
 * 注意：创建envronment时，如果SqlSessionFactoryBuilder指定了特定的环境（即数据源）； 
 *      则返回指定环境（数据源）的Environment对象，否则返回默认的Environment对象； 
 *      这种方式实现了MyBatis可以连接多数据源 
 */ 
private void environmentsElement(XNode context) throws Exception { 
 if (context != null) 
 { 
 if (environment == null) 
 { 
            environment = context.getStringAttribute("default"); 
 } 
 for (XNode child : context.getChildren()) 
 { 
 String id = child.getStringAttribute("id"); 
 if (isSpecifiedEnvironment(id)) 
 { 
 //1.创建事务工厂 TransactionFactory 
 TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager")); 
 DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource")); 
 //2.创建数据源DataSource 
 DataSource dataSource = dsFactory.getDataSource(); 
 //3. 构造Environment对象 
 Environment.Builder environmentBuilder = new Environment.Builder(id) 
 .transactionFactory(txFactory) 
 .dataSource(dataSource); 
 //4. 将创建的Envronment对象设置到configuration 对象中 
 configuration.setEnvironment(environmentBuilder.build()); 
 } 
 } 
 } 
}
private boolean isSpecifiedEnvironment(String id) 
{ 
 if (environment == null) 
 { 
 throw new BuilderException("No environment specified."); 
 } 
 else if (id == null) 
 { 
 throw new BuilderException("Environment requires an id attribute."); 
 } 
 else if (environment.equals(id)) 
 { 
 return true; 
 } 
 return false; 
} 

String resource = "mybatis-config.xml"; 
InputStream inputStream = Resources.getResourceAsStream(resource); 
// 手动创建XMLConfigBuilder，并解析创建Configuration对象 
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, null,null); // 看这里 
Configuration configuration = parser.parse(); 
// 使用Configuration对象创建SqlSessionFactory 
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration); 
// 使用MyBatis 
SqlSession sqlSession = sqlSessionFactory.openSession(); 
List list = sqlSession.selectList("com.foo.bean.BlogMapper.queryAllBlogInfo");