mybatis笔记3 一些原理的理解

1，mybatis流程跟踪，原理理解

基本思路： 从SqlSessionFactory的初始化出发，观察资源的准备和环境的准备，以及实现持久层的一些过程；

进入SqlSessionFactoryBean类，发现先执行的是

然后是：

在初始化类之后，做的准备工作如下：

public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");//1，检查spring准备的datasource是否ok
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");//2,检查空构造方法的sqlSessionFactoryBuilder是否准备好

this.sqlSessionFactory = buildSqlSessionFactory();//3，利用配置的属性，构造sqlSessionFactory
  }

构造细节如下：方法有点长，注意注释这个是流程，之后我画一个图来加深理解；

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

Configuration configuration;

XMLConfigBuilder xmlConfigBuilder = null;
   if (this.configLocation != null) {//1，检查是否有配置configLocation，即mybatis的整体配置文件，非mapper文件，如果有加载进去，没有，构造一个空的
     xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
     configuration = xmlConfigBuilder.getConfiguration();
   } else {
     if (logger.isDebugEnabled()) {
       logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration");
     }
     configuration = new Configuration();
     configuration.setVariables(this.configurationProperties);
   }

if (this.objectFactory != null) {//2,检查对象工厂，如果有设置进去，没有留空
     configuration.setObjectFactory(this.objectFactory);
   }

if (this.objectWrapperFactory != null) {//3,检查对象装饰工厂，如果有设置进去，没有留空

configuration.setObjectWrapperFactory(this.objectWrapperFactory);
   }

if (hasLength(this.typeAliasesPackage)) {//4,检查包的简称，如果有注册进去
     String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
         ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
     for (String packageToScan : typeAliasPackageArray) {
       configuration.getTypeAliasRegistry().registerAliases(packageToScan,
               typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
       if (logger.isDebugEnabled()) {
         logger.debug("Scanned package: '" + packageToScan + "' for aliases");
       }
     }
   }

if (!isEmpty(this.typeAliases)) {//5,检查类的简称，如果有注册进去
     for (Class<?> typeAlias : this.typeAliases) {
       configuration.getTypeAliasRegistry().registerAlias(typeAlias);
       if (logger.isDebugEnabled()) {
         logger.debug("Registered type alias: '" + typeAlias + "'");
       }
     }
   }

if (!isEmpty(this.plugins)) {//6，检查插件，如果有注册进去
     for (Interceptor plugin : this.plugins) {
       configuration.addInterceptor(plugin);
       if (logger.isDebugEnabled()) {
         logger.debug("Registered plugin: '" + plugin + "'");
       }
     }
   }

if (hasLength(this.typeHandlersPackage)) {//7,检查类型转换类包，如果有注册进去
     String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
         ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
     for (String packageToScan : typeHandlersPackageArray) {
       configuration.getTypeHandlerRegistry().register(packageToScan);
       if (logger.isDebugEnabled()) {
         logger.debug("Scanned package: '" + packageToScan + "' for type handlers");
       }
     }
   }

if (!isEmpty(this.typeHandlers)) {//8,检查类型转换类，如果有注册进去
     for (TypeHandler<?> typeHandler : this.typeHandlers) {
       configuration.getTypeHandlerRegistry().register(typeHandler);
       if (logger.isDebugEnabled()) {
         logger.debug("Registered type handler: '" + typeHandler + "'");
       }
     }
   }

if (xmlConfigBuilder != null) {//9,检查是否有xml的构造器，如果有，直接使用构造器构造
     try {
       xmlConfigBuilder.parse();

if (logger.isDebugEnabled()) {
         logger.debug("Parsed configuration file: '" + this.configLocation + "'");
       }
     } catch (Exception ex) {
       throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
     } finally {
       ErrorContext.instance().reset();
     }
   }

if (this.transactionFactory == null) {//10,检查事物工厂，如果没有，构造一个spring管理的事物工厂
     this.transactionFactory = new SpringManagedTransactionFactory();
   }

//11，构造环境变量

Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource);
   configuration.setEnvironment(environment);

if (this.databaseIdProvider != null) {
     try {//12，检查是否配置了db id，如果有，设置到配置的类中
       configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
     } catch (SQLException e) {
       throw new NestedIOException("Failed getting a databaseId", e);
     }
   }

if (!isEmpty(this.mapperLocations)) {//13，把配置的mapper弄进来总配置文件里
     for (Resource mapperLocation : this.mapperLocations) {
       if (mapperLocation == null) {
         continue;
       }

try {
         XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
             configuration, mapperLocation.toString(), configuration.getSqlFragments());
         xmlMapperBuilder.parse();
       } catch (Exception e) {
         throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
       } finally {
         ErrorContext.instance().reset();
       }

if (logger.isDebugEnabled()) {
         logger.debug("Parsed mapper file: '" + mapperLocation + "'");
       }
     }
   } else {
     if (logger.isDebugEnabled()) {
       logger.debug("Property 'mapperLocations' was not specified or no matching resources found");
     }
   }

return this.sqlSessionFactoryBuilder.build(configuration);//14，最后通过得到的配置类来构造一个sqlsessionFactory工厂
}

设置好属性之后，执行

得到factory构造的bean，即sqlSessionFactory,

最后容器启动成功的事件监控

public void onApplicationEvent(ApplicationEvent event) {
   if (failFast && event instanceof ContextRefreshedEvent) {
     // fail-fast -> check all statements are completed
     this.sqlSessionFactory.getConfiguration().getMappedStatementNames();
   }
}

以上是资源的准备，下面来一次增删改查的跟踪，观察内部的工作原理；

查询单条记录的过程：

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
  try {
    MappedStatement ms = configuration.getMappedStatement(statement);//1，通过转换，得到存储的mapperedStatement
    List<E> result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);//2，转换成jdbc代码执行
    return result;
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}

内部就像是一台精密的仪器，去除了大量的模版jdbc代码；