MyBatis源码阅读-总索引

前言

SqlSessionFactory 用于根据配置文件生成的配置类Configuration创建SqlSession。

继承体系

可以看到SqlSessionFactory接口有两个实现类DefaultSqlSessionFactory和SqlSessionManager，SqlSessionManager还实现了SqlSession接口，SqlSessionFactoryBuilder中是使用DefaultSqlSessionFactory来创建SqlSessionFactory，本文章只介绍DefaultSqlSessionFactory。

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

源码分析

私有属性

只有一个私有属性Configuration对象，其由由MyBatis配置文件转化而成。

 private final Configuration configuration;

构造器

只有一个构造器，参数为Configuration类对象

 public DefaultSqlSessionFactory(Configuration configuration) {this.configuration = configuration;}

openSession()获取SqlSession

可以看到openSession主要要以下几个入参

• autoCommit :
  true：自动提交，无需再显示调用sqlSession.commit();进行提交。
  false：不自动提交，需再显示调用sqlSession.commit();进行提交，否则更新删除插入操作无效。
• ExecutorType
  配置默认的执行器。SIMPLE 就是普通的执行器；REUSE 执行器会重用预处理语句（prepared statements）； BATCH 执行器将重用语句并执行批量更新。
• TransactionIsolationLevel：
• TransactionIsolationLevel事务相关的隔离等级，用于解决脏读，不可重复读等并发问题，后面会有文章进行相关介绍。
  READ_COMMITTED：读提交
  READ_UNCOMMITTED： 读未提交
  REPEATABLE_READ：可重复读
  SERIALIZABLE：可序列化

√: 可能出现 ×: 不会出现

    public SqlSession openSession() {return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, false);}public SqlSession openSession(boolean autoCommit) {return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, autoCommit);}public SqlSession openSession(ExecutorType execType) {return this.openSessionFromDataSource(execType, (TransactionIsolationLevel)null, false);}public SqlSession openSession(TransactionIsolationLevel level) {return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), level, false);}public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {return this.openSessionFromDataSource(execType, level, false);}public SqlSession openSession(ExecutorType execType, boolean autoCommit) {return this.openSessionFromDataSource(execType, (TransactionIsolationLevel)null, autoCommit);}public SqlSession openSession(Connection connection) {return this.openSessionFromConnection(this.configuration.getDefaultExecutorType(), connection);}public SqlSession openSession(ExecutorType execType, Connection connection) {return this.openSessionFromConnection(execType, connection);}

上面的openSession都是通过调用openSessionFromDataSource来创建SqlSession。
最终是根据相关配置使用DefaultSqlSession类来创建SqlSession对象。
var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;DefaultSqlSession var8;try {Environment environment = this.configuration.getEnvironment();TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);Executor executor = this.configuration.newExecutor(tx, execType);var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);} catch (Exception var12) {this.closeTransaction(tx);throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);} finally {ErrorContext.instance().reset();}return var8;}//Connection  ： java.sql.Connectionprivate SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {DefaultSqlSession var8;try {boolean autoCommit;try {autoCommit = connection.getAutoCommit();} catch (SQLException var13) {autoCommit = true;}Environment environment = this.configuration.getEnvironment();TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);Transaction tx = transactionFactory.newTransaction(connection);Executor executor = this.configuration.newExecutor(tx, execType);var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);} catch (Exception var14) {throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var14, var14);} finally {ErrorContext.instance().reset();}return var8;}

获取TransactionFactory

    private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {return (TransactionFactory)(environment != null && environment.getTransactionFactory() != null ? environment.getTransactionFactory() : new ManagedTransactionFactory());}