private Properties settingsAsProperties(XNode context) {
    if (context == null) {
      return new Properties();
    }
    Properties props = context.getChildrenAsProperties();
    // Check that all settings are known to the configuration class
    //檢驗(yàn)所有的settings節(jié)點(diǎn)是否在Configuration的定義中
    MetaClass metaConfig = MetaClass.forClass(Configuration.class, localReflectorFactory);
    for (Object key : props.keySet()) {
      if (!metaConfig.hasSetter(String.valueOf(key))) {
        throw new BuilderException("The setting " + key + " is not known.  Make sure you spelled it correctly (case sensitive).");
      }
    }
    return props;
  }

• 第一加載了settings下的property節(jié)點(diǎn)，檢驗(yàn)是否都在Configuration中已經(jīng)定義。
  MetaClass是一個(gè)保存對象定義的元數(shù)據(jù)類，localReflectorFactory是mybatis提供的默認(rèn)反射工廠實(shí)現(xiàn)，這個(gè)ReflectorFactory主要采用了工廠類，其內(nèi)部使用的Reflector采用了facade設(shè)計(jì)模式，簡化反射的使用。

public class MetaClass {

  private ReflectorFactory reflectorFactory;
  private Reflector reflector;

  private MetaClass(Class<?> type, ReflectorFactory reflectorFactory) {
    this.reflectorFactory = reflectorFactory;
    this.reflector = reflectorFactory.findForClass(type);
  }

  public static MetaClass forClass(Class<?> type, ReflectorFactory reflectorFactory) {
    return new MetaClass(type, reflectorFactory);
  }
  ...
}
  @Override
  public Reflector findForClass(Class<?> type) {
    if (classCacheEnabled) {
      // synchronized (type) removed see issue #461
      Reflector cached = reflectorMap.get(type);
      if (cached == null) {
        cached = new Reflector(type);
        reflectorMap.put(type, cached);
      }
      return cached;
    } else {
      return new Reflector(type);
    }
  }
  public Reflector(Class<?> clazz) {
    type = clazz;
    addDefaultConstructor(clazz);
    addGetMethods(clazz);
    addSetMethods(clazz);
    addFields(clazz);
    readablePropertyNames = getMethods.keySet().toArray(new String[getMethods.keySet().size()]);
    writeablePropertyNames = setMethods.keySet().toArray(new String[setMethods.keySet().size()]);
    for (String propName : readablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
    for (String propName : writeablePropertyNames) {
      caseInsensitivePropertyMap.put(propName.toUpperCase(Locale.ENGLISH), propName);
    }
  }

• 再得到settings后將值賦給了configuration

 private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      //獲取settings
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      //賦值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);
    }
  }

• 這里將覆蓋了原來mybatis的默認(rèn)值，有可能mybatis定義的默認(rèn)值不是真實(shí)的默認(rèn)值。