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在以前文章中，咱们把Mybatis源码浏览的整个流程梳理了一遍。明天，咱们来具体聊聊，Mybatis是如何解析配置文件的。
这是明天剖析的流程图：
还是从案例开始。
demo案例
public static void main(String[] args) { String resource = "mybatis-config.xml"; InputStream inputStream = null; SqlSession sqlSession = null; try { inputStream = Resources.getResourceAsStream(resource); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); sqlSession = sqlSessionFactory.openSession(); UserMapper userMapper = sqlSession.getMapper(UserMapper.class); System.out.println(userMapper.selectById(1)); } catch (Exception e) { e.printStackTrace(); } finally { try { inputStream.close(); } catch (IOException e) { e.printStackTrace(); } sqlSession.close(); } }见证奇观
从SqlSessionFactoryBuilder开始。
SqlSessionFactoryBuilder类
org.apache.ibatis.session.SqlSessionFactoryBuilder该类里全是build办法各种重载。
//这个办法啥也没干 public SqlSessionFactory build(InputStream inputStream) { return build(inputStream, null, null); }最终来到另外一个build办法里：
public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { //创立一个XMLConfigBuilder对象 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. } } }XMLConfigBuilder类
该类的构造方法重载：
首先进入：
public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) { this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);}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;}build(parser.parse());中的parser.parse()；
mybatis-config.xml在哪里解析的呢？
请看上面这个办法：
//该办法返回一个Configuration对象public Configuration parse() { if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; //关键点 parseConfiguration(parser.evalNode("/configuration")); return configuration;}parseConfiguration(parser.evalNode("/configuration"));
终于看到开始解析配置文件了:
进入办法parseConfiguration。
private void parseConfiguration(XNode root) { try { //issue #117 read properties first propertiesElement(root.evalNode("properties")); Properties settings = settingsAsProperties(root.evalNode("settings")); loadCustomVfs(settings); loadCustomLogImpl(settings); typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); reflectorFactoryElement(root.evalNode("reflectorFactory")); 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); } }这里就是把mybatis-config.xml内容解析，而后设置到Configuration对象中。
那么咱们定义的Mapper.xml是在哪里解析的呢？
咱们的Mapper.xml在mybatis-config.xml中的配置是这样的：
<mapper>应用形式有以下四种：
//1应用类门路<mappers> <mapper resource="org/mybatis/builder/AuthorMapper.xml"/> <mapper resource="org/mybatis/builder/BlogMapper.xml"/> <mapper resource="org/mybatis/builder/PostMapper.xml"/></mappers>//2应用相对url门路<mappers> <mapper url="file:///var/mappers/AuthorMapper.xml"/> <mapper url="file:///var/mappers/BlogMapper.xml"/> <mapper url="file:///var/mappers/PostMapper.xml"/></mappers>//3应用java类名<mappers> <mapper class="org.mybatis.builder.AuthorMapper"/> <mapper class="org.mybatis.builder.BlogMapper"/> <mapper class="org.mybatis.builder.PostMapper"/></mappers>//4主动扫描包下所有映射器<mappers> <package name="org.mybatis.builder"/></mappers>持续源码剖析，咱们在下面mybatis-config.xml解析中能够看到：
咱们无妨进入这个办法看看：
private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { //主动扫描包下所有映射器 if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); //放 configuration.addMappers(mapperPackage); } else { String resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); //应用java类名 if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); //依据文件寄存目录，读取XxxMapper.xml InputStream inputStream = Resources.getResourceAsStream(resource); //映射器比较复杂，调用XMLMapperBuilder //留神在for循环里每个mapper都从新new一个XMLMapperBuilder，来解析 XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); mapperParser.parse(); //应用相对url门路 } else if (resource == null && url != null && mapperClass == null) { ErrorContext.instance().resource(url); InputStream inputStream = Resources.getUrlAsStream(url); //映射器比较复杂，调用XMLMapperBuilder XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); //应用类门路 } else if (resource == null && url == null && mapperClass != null) { Class<?> mapperInterface = Resources.classForName(mapperClass); //间接把这个映射退出配置 configuration.addMapper(mapperInterface); } else { throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one."); } } } } }这里刚刚和咱们的下面说的<mapper>应用的形式齐全是截然不同的。
到这里，配置文件mybatis-config.xml和咱们定义映射文件XxxMapper.xml就全副解析实现。
回到SqlSessionFactoryBuilder类
后面讲到了XMLConfigBuilder中的parse办法，并返回了一个Configuration对象。
build(parser.parse());
这个build办法就是传入一个Configuration对象，而后构建一个DefaultSqlSession对象。
public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); }持续回到咱们的demo代码中这一行代码里：
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);这一行代码就相当于：
SqlSessionFactory sqlSessionFactory = new new DefaultSqlSessionFactory();到这里，咱们的整个流程就搞定了。
举荐浏览
Mybatis 中xml和注解映射，so easy啦