在继续深入之前我们需要了解一下XMLConfigBuilder这个对象,从名字上来看就可以知道是解析XML配置文件的;XMLConfigBuilder又继承了BaseBuilder类,而在BaseBuilder类中有一个属性Configuration,这个Configuration对象就是用来存储全局配置文件和其他Mapper的配置信息, 同时我们从下图也可以看到XMLMapperBuilder,XMLStatementBuilder,MapperBuilderAssistant也继承了BaseBuilder类
XMLxxxBuilder是用来解析XML配置文件的，不同类型XMLxxxBuilder用来解析MyBatis配置文件的不同部位。
XMLConfigBuilder用来解析MyBatis的全局配置文件
XMLMapperBuilder用来解析MyBatis中的映射文件
XMLStatementBuilder用来解析映射文件中的statement语句。
MapperBuilderAssistant用来辅助解析映射文件并生成MappedStatement对象
这些XMLxxxBuilder都有一个共同的父类——BaseBuilder。这个父类维护了一个全局的Configuration对象，MyBatis的配置文件解析后就以Configuration对象的形式存储
看源码果然能发现猫腻,不错不错,可以看到在new这个XMLConfigBuilder对象的时候,下图的断点位置super(new Configuration());
可以看到Configuration的构造方法如下所示,这也正解释了我们我们可以在全局配置文件中写个JDBC就行,因为在Configuration对象在构建的时候就加载了一些默认的别名. 别告诉我你不知道别名是啥哈~~
public Configuration() {
this.safeResultHandlerEnabled = true;
this.multipleResultSetsEnabled = true;
this.useColumnLabel = true;
this.cacheEnabled = true;
this.useActualParamName = true;
this.localCacheScope = LocalCacheScope.SESSION;
this.jdbcTypeForNull = JdbcType.OTHER;
this.lazyLoadTriggerMethods = new HashSet(Arrays.asList("equals", "clone", "hashCode", "toString"));
this.defaultExecutorType = ExecutorType.SIMPLE;
this.autoMappingBehavior = AutoMappingBehavior.PARTIAL;
this.autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
this.variables = new Properties();
this.reflectorFactory = new DefaultReflectorFactory();
this.objectFactory = new DefaultObjectFactory();
this.objectWrapperFactory = new DefaultObjectWrapperFactory();
this.lazyLoadingEnabled = false;
this.proxyFactory = new JavassistProxyFactory();
this.mapperRegistry = new MapperRegistry(this);
this.interceptorChain = new InterceptorChain();
this.typeHandlerRegistry = new TypeHandlerRegistry();
this.typeAliasRegistry = new TypeAliasRegistry();
this.languageRegistry = new LanguageDriverRegistry();
this.mappedStatements = new Configuration.StrictMap("Mapped Statements collection");
this.caches = new Configuration.StrictMap("Caches collection");
this.resultMaps = new Configuration.StrictMap("Result Maps collection");
this.parameterMaps = new Configuration.StrictMap("Parameter Maps collection");
this.keyGenerators = new Configuration.StrictMap("Key Generators collection");
this.loadedResources = new HashSet();
this.sqlFragments = new Configuration.StrictMap("XML fragments parsed from previous mappers");
this.incompleteStatements = new LinkedList();
this.incompleteCacheRefs = new LinkedList();
this.incompleteResultMaps = new LinkedList();
this.incompleteMethods = new LinkedList();
this.cacheRefMap = new HashMap();
this.typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
this.typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
this.typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
this.typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
this.typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
this.typeAliasRegistry.registerAlias("LRU", LruCache.class);
this.typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
this.typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
this.typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
this.typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
this.typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
this.typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
this.typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
this.typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
this.typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
this.typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
this.typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
this.typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
this.typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
this.languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
this.languageRegistry.register(RawLanguageDriver.class);
}
