技術標籤：MYBATISmybatis

在Mybatis的配置檔案，我們以 SqlSessionFactoryBuilder 去建立 SqlSessionFactory, 那麼，我們就先從SqlSessionFactoryBuilder入手， 咱們先看看原始碼是怎麼實現的：

SqlSessionFactoryBuilder程式碼片斷：.

public class SqlSessionFactoryBuilder {

  //Reader讀取mybatis配置檔案，傳入構造方法
  //除了Reader外，其實還有對應的inputStream作為引數的構造方法，
  //這也體現了mybatis配置的靈活性
 

  public SqlSessionFactory build(Reader reader) {
    return build(reader, null, null);
  }

  public SqlSessionFactory build(Reader reader, String environment) {
    return build(reader, environment, null);
  }

  //mybatis配置檔案 + properties, 此時mybatis配置檔案中可以不配置properties，也能使用${}形式
  public SqlSessionFactory build
 
(Reader reader, Properties properties) {
    return build(reader, null, properties);
  }

  //通過XMLConfigBuilder解析mybatis配置，然後建立SqlSessionFactory物件
  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder
 
(reader, environment, properties);
      //下面看看這個方法的原始碼
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

}

通過原始碼，我們可以看到SqlSessionFactoryBuilder 通過XMLConfigBuilder 去解析我們傳入的mybatis的配置檔案， 下面就接著看看 XMLConfigBuilder 部分原始碼：

/**
 * mybatis 配置檔案解析
 */
public class XMLConfigBuilder extends BaseBuilder {
  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;
  }

  //外部呼叫此方法對mybatis配置檔案進行解析
  public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    //從根節點configuration
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }

  //此方法就是解析configuration節點下的子節點
  //由此也可看出，我們在configuration下面能配置的節點為以下10個節點
  private void parseConfiguration(XNode root) {
    try {
      propertiesElement(root.evalNode("properties")); //issue #117 read properties first
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      settingsElement(root.evalNode("settings"));
      environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631
      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);
    }
  }
}

通過以上原始碼，我們就能看出，在mybatis的配置檔案中：

1. configuration節點為根節點。

2. 在configuration節點之下，我們可以配置10個子節點， 分別為：properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。