Configuration(三)

最新推荐文章于 2025-10-13 12:12:08 发布

原创最新推荐文章于 2025-10-13 12:12:08 发布 · 1.6k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#mybatis

mybatis 专栏收录该内容

16 篇文章

订阅专栏

本文详细剖析了MyBatis框架中Configuration对象的构建过程，包括XMLConfigBuilder如何通过parser.parse()方法将XML配置文件转化为Configuration对象，以及Configuration构造方法中的初始化设置。

上一篇文章中,我们找到了新的切入点Configuration,现在就让我们来看看parser.parse()是怎么样把xml配置文件转化成Configuration的.

我们先来看XMLConfigBuilder的构造方法:

  public XMLConfigBuilder(Reader reader, String environment, Properties props) {
    this(new XPathParser(reader, 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;
  }

  // 这是XMLConfigBuilder父类构造方法,也就是super(new Configuration())
  public BaseBuilder(Configuration configuration) {
    this.configuration = configuration;
    this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
    this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
  }

其他的类我们不管,都是解析xml的类,不是本系列文章关注的重点,我们主要来看Configuration相关内容.可以看到在构造方法中new Configuration(),将实例化一个Configuration实例赋值给成员变量configuration.

我们来看看Configuration类的构造方法:

  protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
  protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();

  public Configuration() {
    typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
    typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);

    typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
    typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
    typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);

    typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
    typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
    typeAliasRegistry.registerAlias("LRU", LruCache.class);
    typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
    typeAliasRegistry.registerAlias("WEAK", WeakCache.class);

    typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);

    typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
    typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);

    typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
    typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
    typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
    typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
    typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
    typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
    typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);

    typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
    typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);

    languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
    languageRegistry.register(RawLanguageDriver.class);
  }

我们可以看到Configuration的构造方法中好像干了很多事情,其实就是进行了一些别名的默认设置,typeAliasRegistry和languageRegistry内部都是封装了一个HashMap来存储数据.这些我们先不关注,我们先来看看parser.parse()方法:

  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    // 真正的处理逻辑,parser.evalNode("/configuration")获取了xml文件中最外层的<configuration>节点
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  // 该方法中,将<configuration>下的所有节点分开处理,一个方法处理一个节点,理所当然,这些处理中肯定是对configuration成员变量中设置了所有配置文件中的信息.
  private void parseConfiguration(XNode root) {
    try {
      propertiesElement(root.evalNode("properties"));
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      settingsElement(root.evalNode("settings"));
      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);
    }
  }