mybatis SqlSessionFactory . openSession()方法执行过程

//false: 不自动提交
SqlSession sqlSession = factory.openSession(false);

public class DefaultSqlSessionFactory implements SqlSessionFactory {

//DefaultSqlSessionFactory 中唯一成员变量
private final Configuration configuration;

@Override
public SqlSession openSession(boolean autoCommit) {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
}

//configuration.getDefaultExecutorType() 得到的结果就是默认的 ExecutorType.SIMPLE;
public class Configuration {

//ExecutorType.SIMPLE: 这个执行器类型不做特殊的事情。它为每个语句的执行创建一个新的预处理语句。
//ExecutorType.REUSE: 这个执行器类型会复用预处理语句。
//ExecutorType.BATCH: 这个执行器会批量执行所有更新语句,如果 SELECT 在它们中间执行还会标定它们是 必须的,来保证一个简单并易于理解的行为。

protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
}

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;

//通过configuration(封装<configration>所有信息);获取到Environment信息(<environment>)
final Environment environment = configuration.getEnvironment();

//从Environment中获取TransactionFactory
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);

private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
if (environment == null || environment.getTransactionFactory() == null) {
return new ManagedTransactionFactory();
}
return environment.getTransactionFactory();
}

//TransactionFactory是Environment类中的对象属性
public final class Environment {
private final String id;
private final TransactionFactory transactionFactory;
private final DataSource dataSource;
}

//transactionFactory创建一个事务 : 传参数 -- environment.数据源, level : 事务隔离级别, 自动提交
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);	//555

//根据execType类型, 和事务对象, 创建一个执行器
final Executor executor = configuration.newExecutor(tx, execType);			//666

//创建DefaultSqlSession: 根据配置对象configuration, 执行器 executor, 自动提交boolean值
return new DefaultSqlSession(configuration, executor, autoCommit);			//777

}

}

//返回一个ManagedTransaction对象(TransactionFactory 实现类)
public class ManagedTransactionFactory implements TransactionFactory {//555

private boolean closeConnection = true;

@Override
public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
return new ManagedTransaction(ds, level, closeConnection);
}

}

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {//666

executorType = executorType == null ? defaultExecutorType : executorType;
executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
Executor executor;
if (ExecutorType.BATCH == executorType) {
executor = new BatchExecutor(this, transaction);
} else if (ExecutorType.REUSE == executorType) {
executor = new ReuseExecutor(this, transaction);
} else {
executor = new SimpleExecutor(this, transaction);
}
if (cacheEnabled) {//默认true
executor = new CachingExecutor(executor);
}

//装饰模式, 将SimpleExecutor 装饰到 CachingExcutor
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;

}

//创建一个SqlSession子类DefaultSqlSession对象返回, openSession()方法获得了SqlSession
public class DefaultSqlSession implements SqlSession { // 777

private final Configuration configuration;
private final Executor executor;
private final boolean autoCommit;
private boolean dirty;

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}

}