SqlSessionFactoryBuilder是构建sqlSessionFactory的入口类
从该类的方法可知，它是通过不同的入参来构造SqlSessionFactory，除了最后一个configuration入参方法外，其余方法最终都调用如下方法
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); return build(parser.parse()); } 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. } } }
如上图所示，先创建了一个XMLConfigBuilder类的实例
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) { this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props); }
在这个初始化过程中，首先创建了XMLMapperEntityResolver类的实例，这个类顾名思义是个实体mapper文件实体解析器，里面有个map将mybatis的xml文件与对应的解析文件关系保存起来。初始化后再实例化XPathParser
public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) { commonConstructor(validation, variables, entityResolver); this.document = createDocument(new InputSource(inputStream)); }
private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) { this.validation = validation; this.entityResolver = entityResolver; this.variables = variables; XPathFactory factory = XPathFactory.newInstance(); this.xpath = factory.newXPath(); }
commonConstructor比较简单，就是给一些类变量赋值，并且初始化了一个xpath对象，这里使用了工厂设计模式。
new InputSource(inputStream)就是将输入流赋予自己内部的一个变量byteStream。
createDocument(new InputSource(inputStream))这里面主要做了这几件事通过DocumentBuilderFactory生成DocumentBuilder，并将entityResolver赋给它的属性字段同时定义了一个处理异常的内部类，
然后通过builder.parse(inputSource)将输入流解析成一个document对象。
private XMLConfigBuilder(XPathParser parser, String environment, Properties props) { super(new Configuration()); ErrorContext.instance().resource("SQL Mapper Configuration"); this.configuration.setVariables(props); this.parsed = false; this.environment = environment; this.parser = parser; }
new Configuration()主要是在构造方法里面注册了别名
typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
registerAlias是TypeAliasRegistry类的方法，将别名与类的关系保存在了内部的private final Map<String, Class<?>> TYPE_ALIASES
public BaseBuilder(Configuration configuration) { this.configuration = configuration; this.typeAliasRegistry = this.configuration.getTypeAliasRegistry(); this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry(); }
super(new Configuration())就是将相应的变量保存在父类属性上，方便其它子类使用。
ErrorContext.instance()方法内部采用的threadlocal方式，每个线程都持有一个ErrorContext对象resource("SQL Mapper Configuration")就是一个简单的赋值给resource变量方法。
至此一个XMLConfigBuilder对象就创建出来了，然后就进入了build(parser.parse())。
public Configuration parse() { if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; parseConfiguration(parser.evalNode("/configuration")); return configuration; }
parser.evalNode("/configuration")在初始化过程中已经将mybatis_config.xml文件解析成document对象，这里使用xpath解析工具将configuration节点解析成一个XNode对象。
private void parseConfiguration(XNode root) { try { Properties settings = settingsAsPropertiess(root.evalNode("settings")); //issue #117 read properties first propertiesElement(root.evalNode("properties")); loadCustomVfs(settings); typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); reflectionFactoryElement(root.evalNode("reflectionFactory")); settingsElement(settings); // read it after objectFactory and objectWrapperFactory issue #631 environmentsElement(root.evalNode("environments")); databaseIdProviderElement(root.evalNode("databaseIdProvider")); typeHandlerElement(root.evalNode("typeHandlers")); mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } }
mybatis随笔一之SqlSessionFactoryBuilder
原文：http://www.cnblogs.com/tuifeideyouran/p/6393704.html