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  • MyBatis框架的使用及源码分析(二) 配置篇 SqlSessionFactoryBuilder,XMLConfigBuilder

    在 <MyBatis框架中Mapper映射配置的使用及原理解析(一) 配置与使用> 的demo中看到了SessionFactory的创建过程:

    SqlSessionFactory sessionFactory = null;
            String resource = "mybatisConfig.xml";
            try {
                sessionFactory = new SqlSessionFactoryBuilder().build(Resources
                        .getResourceAsReader(resource));
            } catch (IOException e) {
                e.printStackTrace();
            }

    那么我们就从SqlSessionFactoryBuilder开始,看看Mybatis的加载过程。

    SqlSessionFactoryBuilder的核心源码:

    package org.apache.ibatis.session;
    public class SqlSessionFactoryBuilder {
    //通过Reader读取Mybatis配置
     public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        try {      
          XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
          return build(parser.parse()); //parse()方法得到Configuration
        } 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.
          }
        }
      }
    
    //通过InputStream读取Mybatis配置
    public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); return build(parser.parse()); //parse()方法得到Configuration } 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. } } }
    //以上2个方法最终调用的是build(Configuration config)
    public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); } }

    通过源码,我们可以看到SqlSessionFactoryBuilder 通过XMLConfigBuilder 去解析我们传入的mybatis的配置文件,构造出Configuration,最终返回new DefaultSqlSessionFactory(config)的SqlSessionFactory实例。

    接下来我们看看 XMLConfigBuilder 是怎样解析Mybatis的配置文件的,下面是部分源码:

    package org.apache.ibatis.builder.xml;
    
    
    /**
     * 解析Mybatis配置文件
     */
    public class XMLConfigBuilder extends BaseBuilder {
    
      private boolean parsed;
      private XPathParser parser;
      private String environment;
    
      public XMLConfigBuilder(Reader reader) {
        this(reader, null, null);
      }
    
      public XMLConfigBuilder(Reader reader, String environment) {
        this(reader, environment, null);
      }
    
      public XMLConfigBuilder(Reader reader, String environment, Properties props) {
        this(new XPathParser(reader, true, props, new XMLMapperEntityResolver()), environment, props);
      }
    
      public XMLConfigBuilder(InputStream inputStream) {
        this(inputStream, null, null);
      }
    
      public XMLConfigBuilder(InputStream inputStream, String environment) {
        this(inputStream, environment, null);
      }
    
      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;
      }
    
      //调用此方法对mybatis配置文件进行解析,返回Configuration对象
      public Configuration parse() {
        if (parsed) {
          throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        }
        parsed = true;
        //从根节点configuration,开始解析
        parseConfiguration(parser.evalNode("/configuration"));
        return configuration;
      }
      
      //解析configuration节点下的10个子节点。
      private void parseConfiguration(XNode root) {
        try {
    //解析子节点properties  propertiesElement(root.evalNode(
    "properties")); //issue #117 read properties first
    //解析子节点typeAliases 别名 typeAliasesElement(root.evalNode("typeAliases"));
    //解析子节点plugins 插件  pluginElement(root.evalNode(
    "plugins"));
    //解析子节点objectFactory mybatis为结果创建对象时都会用到objectFactory objectFactoryElement(root.evalNode(
    "objectFactory"));
    //解析子节点objectWrapperFactory objectWrapperFactoryElement(root.evalNode(
    "objectWrapperFactory"));
    //解析settings定义一些全局性的配置 settingsElement(root.evalNode(
    "settings"));
    //解析environments 可以配置多个运行环境,但是每个SqlSessionFactory 实例只能选择一个运行环境 environmentsElement(root.evalNode(
    "environments")); // read it after objectFactory and objectWrapperFactory issue #631
    //解析databaseIdProvider MyBatis能够执行不同的语句取决于你提供的数据库供应商。许多数据库供应商的支持是基于databaseId映射  databaseIdProviderElement(root.evalNode("databaseIdProvider"));
    //解析typeHandlers 当MyBatis设置参数到PreparedStatement 或者从ResultSet 结果集中取得值时,就会使用TypeHandler  来处理数据库类型与java 类型之间转换 typeHandlerElement(root.evalNode(
    "typeHandlers"));
    //解析mappers 主要的crud操作都是在mappers中定义的 mapperElement(root.evalNode(
    "mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } } }

     从上面可以看出可以配置10个子节点, 分别为:properties、typeAliases、plugins、objectFactory、objectWrapperFactory、settings、environments、databaseIdProvider、typeHandlers、mappers。

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  • 原文地址:https://www.cnblogs.com/zsg88/p/7534690.html
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