MyBatis 源码解析 —— SqlSessionFactory

绝地灬酷狼 2022-10-01 09:51 223阅读 0赞

本文主要分析SqlSessionFactory的构建过程

SqlSessionFactoryBuilder从XML中构建SqlSessionFactory

String resource = "org/mybatis/example/mybatis-config.xml";
    InputStream inputStream = Resources.getResourceAsStream(resource);
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    复制代码

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    复制代码

SqlSessionFactoryBuilder用来创建SqlSessionFactory实例,一旦创建了SqlSessionFactory,就不再需要它了

public SqlSessionFactory build(InputStream inputStream) {
      return build(inputStream, null, null);
    }
    复制代码

调用

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties)
    复制代码

源码如下:

/**
       * 根据配置创建SqlSessionFactory
       *
       * @param inputStream 配置文件输入流
       * @param environment 环境名称
       * @param properties  外部配置
       * @return
       */
      public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        try {
          XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
          //parser.parse()读取配置文件返回configuration
          //build()根据返回的configuration创建SqlSessionFactory
          return build(parser.parse());
        } 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.
          }
        }
      }
    复制代码

最终创建DefaultSqlSessionFactory实例

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

其中

XMLConfigBuilder与Configuration

XMLConfigBuilder的方法parse()

public Configuration parse() {
    	if (parsed) {
    	    throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    	}
    	parsed = true;
    	//读取mybatis-config.xml配置信息,"configuration"是根结点
    	parseConfiguration(parser.evalNode("/configuration"));
    	return configuration;
    }
    复制代码

XMLConfigBuilder的方法parseConfiguration(XNode root)

/**
     * 读取配置文件组装configuration
     * @param root 配置文件的configuration节点
     */
    private void parseConfiguration(XNode root) {
    	try {
    		//issue #117 read properties first
    		propertiesElement(root.evalNode("properties"));
    		typeAliasesElement(root.evalNode("typeAliases"));
    		pluginElement(root.evalNode("plugins"));
    		objectFactoryElement(root.evalNode("objectFactory"));
    		objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
    		reflectionFactoryElement(root.evalNode("reflectionFactory"));
    		settingsElement(root.evalNode("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);
    	}
    }
    复制代码

关于配置文件相关的源码分析参看:

[www.iocoder.cn/MyBatis/udb…][www.iocoder.cn_MyBatis_udb]

##### 设计模式 #####

从SqlSessionFactory和Configuration的创建过程中可以看出它们都使用了建造者模式.

转载于:https://juejin.im/post/5ce79e24518825332a1ef480

[www.iocoder.cn_MyBatis_udb]: https://link.juejin.im?target=http%3A%2F%2Fwww.iocoder.cn%2FMyBatis%2Fudbwcso%2FConfiguration