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@ -0,0 +1,489 @@
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SqlSession是MyBatis核心接口之一，也是MyBatis接口层的主要组成部分，对外提供MyBatis常用的API。mybatis提供了两个SqlSession接口的实现，分别为DefaultSqlSession、SqlSessionManager，其中最常用的是DefaultSqlSession。另外，跟前面分析过的源码mybatis的源码一样，mybatis也为SqlSession提供了相应的工厂接口SqlSessionFactory，及实现该接口的实现DefaultSqlSessionFactory（SqlSessionManager同时实现了SqlSession和SqlSessionFactory接口）。
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## 1 SqlSession
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在SqlSession中定义了常用的数据库操作以及事务的相关操作，为了方便用户使用，每种类型的操作都提供了多种重载。
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```java
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public interface SqlSession extends Closeable {
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// 泛型方法，参数是要执行查询的sql语句，返回值为查询的结果对象
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<T> T selectOne(String statement);
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// 第二个参数表示 需要用户传入的实参，即 sql语句绑定的实参
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<T> T selectOne(String statement, Object parameter);
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// 查询结果有多条记录，会封装成 结果对象列表 并返回
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<E> List<E> selectList(String statement);
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// 参数 + 多记录结果集
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<E> List<E> selectList(String statement, Object parameter);
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// 参数RowBounds主要用于逻辑分页，逻辑分页会将所有的结果都查询到，
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// 然后根据RowBounds中提供的offset和limit值来获取最后的结果
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<E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds);
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// mapKey表示将结果集中的哪一列（如 主键列或编码列）作为Map的key，
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// value则为列值 对应的那条记录
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<K, V> Map<K, V> selectMap(String statement, String mapKey);
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// 多了个parameter参数，其它与上面相同
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<K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey);
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// 多了个RowBounds参数，其它与上面相同
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<K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds);
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// 除了返回值是Cursor对象，其它与selectList相同
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<T> Cursor<T> selectCursor(String statement);
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<T> Cursor<T> selectCursor(String statement, Object parameter);
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<T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds);
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// 查询出的结果集 将由传入的ResultHandler对象处理，其它与selectList相同
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void select(String statement, Object parameter, ResultHandler handler);
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void select(String statement, ResultHandler handler);
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void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler);
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// 执行insert语句
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int insert(String statement);
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int insert(String statement, Object parameter);
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// 执行update语句
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int update(String statement);
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int update(String statement, Object parameter);
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// 执行delete语句
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int delete(String statement);
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int delete(String statement, Object parameter);
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// 提交事务
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void commit();
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void commit(boolean force);
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// 回滚事务
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void rollback();
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void rollback(boolean force);
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// 将对数据库的操作请求 刷到数据库
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List<BatchResult> flushStatements();
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// 关闭当前session
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void close();
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// 清空缓存
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void clearCache();
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// 获取Configuration对象
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Configuration getConfiguration();
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// 获取type对应的Mapper对象
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<T> T getMapper(Class<T> type);
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// 获取该SqlSession对应的数据库连接
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Connection getConnection();
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}
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```
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### 1.1 DefaultSqlSession
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DefaultSqlSession是单独使用MyBatis进行开发时，最常用的SqISession接口实现。其实现了SqISession接口中定义的方法，及各方法的重载。select()系列方法、selectOne()系列方法、selectList()系列方法、selectMap()系列方法之间的调用关系如下图，殊途同归，它们最终都会调用Executor的query()方法。
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上述重载方法最终都是通过调用Executor的query(MappedStatement, Object, RowBounds,ResultHandler)方法实现数据库查询操作的，但各自对结果对象进行了相应的调整，例如：selectOne()方法是从结果对象集合中获取了第一个元素返回；selectMap()方法会将List类型的结果集 转换成Map类型集合返回；select()方法是将结果集交由用户指定的ResultHandler对象处理，且没有返回值；selectList()方法则是直接返回结果对象集合。
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DefaultSqlSession的insert()方法、update()方法、delete()方法也有多个重载，它们最后都是通过调用DefaultSqlSession的update(String, Object)方法实现的，该重载首先会将dirty字段置为true，然后再通过Executor的update()方法完成数据库修改操作。
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DefaultSqlSession的commit()方法、rollback()方法以及close()方法都会调用Executor中相应的方法，其中就会涉及清空缓存的操作，之后就会将dirty字段设置为false。
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上述的dirty字段主要在isCommitOrRollbackRequired()方法中，与autoCommit字段以及用户传入的force参数共同决定是否提交/回滚事务。该方法的返回值将作为Executor的commit()方法和rollback()方法的参数。
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```java
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private boolean isCommitOrRollbackRequired(boolean force) {
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return (!autoCommit && dirty) || force;
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}
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```
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## 2 SqlSessionFactory
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SqlSessionFactory负责创建SqlSession对象，其中包含了多个openSession()方法的重载，可以通过其参数指定事务的隔离级别、底层使用Executor的类型、以及是否自动提交事务等方面的配置。
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```java
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public interface SqlSessionFactory {
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// 提供了openSession()方法的多种重载，根据相应的参数 可以指定事务的隔离级别、
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// 底层使用的Executor类型、以及是否自动提交事务等配置
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SqlSession openSession();
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SqlSession openSession(boolean autoCommit);
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SqlSession openSession(Connection connection);
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SqlSession openSession(TransactionIsolationLevel level);
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SqlSession openSession(ExecutorType execType);
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SqlSession openSession(ExecutorType execType, boolean autoCommit);
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SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);
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SqlSession openSession(ExecutorType execType, Connection connection);
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Configuration getConfiguration();
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}
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```
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### 2.1 DefaultSqlSessionFactory
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DefaultSqlSessionFactory是SqlSessionFactory接口的默认实现，主要提供了两种创建DefaultSqlSession对象的方式，一种方式是通过数据源获取数据库连接，并创建Executor对象以及DefaultSqlSession对象；另一种方式是用户提供数据库连接对象，DefaultSqlSessionFactory根据该数据库连接对象获取autoCommit属性，创建Executor对象以及DefaultSqlSession对象。
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DefaultSqISessionFactory提供的所有openSession()方法重载都是基于上述两种方式创建DefaultSqlSession对象的。
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```java
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public class DefaultSqlSessionFactory implements SqlSessionFactory {
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private final Configuration configuration;
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public DefaultSqlSessionFactory(Configuration configuration) {
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this.configuration = configuration;
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}
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private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
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Transaction tx = null;
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try {
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// 获取配置的Environment对象
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final Environment environment = configuration.getEnvironment();
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// 从environment中获取TransactionFactory对象，如果没有，就创建一个ManagedTransactionFactory实例并返回
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final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
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// 从事务工厂中获取一个事务对象
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tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
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// 根据事务对象tx和配置的Executor类型execType创建Executor实例
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// ExecutorType是个枚举类型，有三个值 SIMPLE, REUSE, BATCH，分别对应了
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// SimpleExecutor、ReuseExecutor、BatchExecutor
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final Executor executor = configuration.newExecutor(tx, execType);
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// 创建DefaultSqlSession对象
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return new DefaultSqlSession(configuration, executor, autoCommit);
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} catch (Exception e) {
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closeTransaction(tx); // may have fetched a connection so lets call close()
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throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
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} finally {
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ErrorContext.instance().reset();
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}
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}
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private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
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try {
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boolean autoCommit;
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try {
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// 根据当前连接对象获取autoCommit属性（是否自动提交事务）
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autoCommit = connection.getAutoCommit();
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} catch (SQLException e) {
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autoCommit = true;
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}
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// 除了获取autoCommit属性的方式和上面不一样外，下面的处理都与上面完全相同
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final Environment environment = configuration.getEnvironment();
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final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
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final Transaction tx = transactionFactory.newTransaction(connection);
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final Executor executor = configuration.newExecutor(tx, execType);
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return new DefaultSqlSession(configuration, executor, autoCommit);
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} catch (Exception e) {
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throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
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} finally {
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ErrorContext.instance().reset();
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}
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}
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private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
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if (environment == null || environment.getTransactionFactory() == null) {
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return new ManagedTransactionFactory();
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}
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return environment.getTransactionFactory();
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}
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private void closeTransaction(Transaction tx) {
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if (tx != null) {
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try {
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tx.close();
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} catch (SQLException ignore) {
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// Intentionally ignore. Prefer previous error.
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}
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}
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}
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@Override
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public SqlSession openSession() {
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return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
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}
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@Override
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public SqlSession openSession(boolean autoCommit) {
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return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
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}
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@Override
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public SqlSession openSession(ExecutorType execType) {
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return openSessionFromDataSource(execType, null, false);
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}
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@Override
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public SqlSession openSession(TransactionIsolationLevel level) {
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return openSessionFromDataSource(configuration.getDefaultExecutorType(), level, false);
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}
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@Override
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public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
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return openSessionFromDataSource(execType, level, false);
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}
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@Override
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public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
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return openSessionFromDataSource(execType, null, autoCommit);
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}
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@Override
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public SqlSession openSession(Connection connection) {
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return openSessionFromConnection(configuration.getDefaultExecutorType(), connection);
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}
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@Override
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public SqlSession openSession(ExecutorType execType, Connection connection) {
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return openSessionFromConnection(execType, connection);
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}
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@Override
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public Configuration getConfiguration() {
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return configuration;
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}
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}
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```
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### 2.2 SqlSessionManager
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SqlSessionManager同时实现了SqlSession接口和SqlSessionFactory接口，所以同时提供了SqlSessionFactory创建SqlSession对象，以及SqlSession操纵数据库的功能。
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SqlSessionManager与DefaultSqlSessionFactory的主要不同点SqlSessionManager 提供了两种模式，第一种模式与DefaultSqlSessionFactory的行为相同，同一线程每次通过SqlSessionManager对象访问数据库时，都会创建新的SqlSession对象完成数据库操作。第二种模式是SqlSessionManager通过localSqlSession这ThreadLocal 变量，记录与当前线程绑定的SqlSession对象，供当前线程循环使用，从而避免在同一线程多次创建SqlSession对象带来的性能损失。
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SqlSessionManager的构造方法是唯一且私有的，如果要创建SqlSessionManager对象，需要调用其newInstance()方法（但需要注意的是，这不是单例模式，因为每次调用newInstance()方法都返回了一个新的对象）。
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SqlSessionManager的openSession()系列方法，都是通过直接调用其持有的
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DefaultSqlSessionFactory实例来实现的。
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```java
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public class SqlSessionManager implements SqlSessionFactory, SqlSession {
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// 通过持有DefaultSqlSessionFactory对象 来产生SqlSession对象
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private final SqlSessionFactory sqlSessionFactory;
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// 用于记录一个与当前线程绑定的SqlSession对象
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private final ThreadLocal<SqlSession> localSqlSession = new ThreadLocal<SqlSession>();
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// localSqlSession中记录的SqlSession对象的代理对象（JDK动态代理）
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// SqlSessionManager初始化时 生成本代理对象，可以看下 下面的构造函数
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private final SqlSession sqlSessionProxy;
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// 私有的构造函数，也是SqlSessionManager唯一的构造函数
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private SqlSessionManager(SqlSessionFactory sqlSessionFactory) {
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// 传入的这个SqlSessionFactory对象 往往是DefaultSqlSessionFactory的实例
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this.sqlSessionFactory = sqlSessionFactory;
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// JDK动态代理生成代理对象，可以看得出，SqlSessionInterceptor一定实现了
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// InvocationHandler接口
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this.sqlSessionProxy = (SqlSession) Proxy.newProxyInstance(
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SqlSessionFactory.class.getClassLoader(),
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new Class[]{SqlSession.class},
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new SqlSessionInterceptor());
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}
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// 通过newInstance()方法创建SqlSessionManager对象，有多种重载，
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// 但最后都是new了一个DefaultSqlSessionFactory的实例
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public static SqlSessionManager newInstance(Reader reader) {
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|
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return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, null));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(Reader reader, String environment) {
|
|
|
|
|
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, environment, null));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(Reader reader, Properties properties) {
|
|
|
|
|
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(reader, null, properties));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(InputStream inputStream) {
|
|
|
|
|
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, null));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(InputStream inputStream, String environment) {
|
|
|
|
|
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, environment, null));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(InputStream inputStream, Properties properties) {
|
|
|
|
|
return new SqlSessionManager(new SqlSessionFactoryBuilder().build(inputStream, null, properties));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public static SqlSessionManager newInstance(SqlSessionFactory sqlSessionFactory) {
|
|
|
|
|
return new SqlSessionManager(sqlSessionFactory);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
// openSession()系列方法都是通过当前SqlSessionManager对象持有的
|
|
|
|
|
// DefaultSqlSessionFactory实例的openSession()实现的
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession() {
|
|
|
|
|
return sqlSessionFactory.openSession();
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(boolean autoCommit) {
|
|
|
|
|
return sqlSessionFactory.openSession(autoCommit);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(Connection connection) {
|
|
|
|
|
return sqlSessionFactory.openSession(connection);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(TransactionIsolationLevel level) {
|
|
|
|
|
return sqlSessionFactory.openSession(level);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(ExecutorType execType) {
|
|
|
|
|
return sqlSessionFactory.openSession(execType);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
|
|
|
|
|
return sqlSessionFactory.openSession(execType, autoCommit);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
|
|
|
|
|
return sqlSessionFactory.openSession(execType, level);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public SqlSession openSession(ExecutorType execType, Connection connection) {
|
|
|
|
|
return sqlSessionFactory.openSession(execType, connection);
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
SqlSessionManager中实现的SqlSession接口方法，例如select ()系列方法、update()系列方法等，都是直接调用sqlSessionProxy代理对象对应的方法实现的。在创建该代理对象时使用的InvocationHandler对象是SqlSessionlnterceptor，它是SqISessionManager的内部类。
|
|
|
|
|
```java
|
|
|
|
|
private class SqlSessionInterceptor implements InvocationHandler {
|
|
|
|
|
|
|
|
|
|
public SqlSessionInterceptor() { }
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
|
|
|
|
|
// 获取 与当前线程绑定的SqlSession
|
|
|
|
|
final SqlSession sqlSession = SqlSessionManager.this.localSqlSession.get();
|
|
|
|
|
// 如果有绑定的SqlSession对象
|
|
|
|
|
if (sqlSession != null) { // 模式二
|
|
|
|
|
try {
|
|
|
|
|
// 调用真正的sqlSession对象，完成数据库操作
|
|
|
|
|
return method.invoke(sqlSession, args);
|
|
|
|
|
} catch (Throwable t) {
|
|
|
|
|
throw ExceptionUtil.unwrapThrowable(t);
|
|
|
|
|
}
|
|
|
|
|
// 如果没有绑定的SqlSession对象
|
|
|
|
|
} else { // 模式一
|
|
|
|
|
// 创建一个新的SqlSession对象
|
|
|
|
|
final SqlSession autoSqlSession = openSession();
|
|
|
|
|
try {
|
|
|
|
|
// 通过反射调用该SqlSession对象的方法，完成数据库操作
|
|
|
|
|
final Object result = method.invoke(autoSqlSession, args);
|
|
|
|
|
// 提交事务
|
|
|
|
|
autoSqlSession.commit();
|
|
|
|
|
return result;
|
|
|
|
|
} catch (Throwable t) {
|
|
|
|
|
// 出异常就回滚
|
|
|
|
|
autoSqlSession.rollback();
|
|
|
|
|
throw ExceptionUtil.unwrapThrowable(t);
|
|
|
|
|
} finally {
|
|
|
|
|
// 关闭该SqlSession对象
|
|
|
|
|
autoSqlSession.close();
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
通过对SqlSessionlnterceptor的分析可知，第一种模式中新建的SqlSession在使用完成后会立即关闭。在第二种模式中，与当前线程绑定的SqISession对象需要先通过SqlSessionManager的startManagedSession()方法进行设置，此方法也存在多种重载，但都彼此相似 且简单。
|
|
|
|
|
```java
|
|
|
|
|
public void startManagedSession() {
|
|
|
|
|
this.localSqlSession.set(openSession());
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(boolean autoCommit) {
|
|
|
|
|
this.localSqlSession.set(openSession(autoCommit));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(Connection connection) {
|
|
|
|
|
this.localSqlSession.set(openSession(connection));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(TransactionIsolationLevel level) {
|
|
|
|
|
this.localSqlSession.set(openSession(level));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(ExecutorType execType) {
|
|
|
|
|
this.localSqlSession.set(openSession(execType));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(ExecutorType execType, boolean autoCommit) {
|
|
|
|
|
this.localSqlSession.set(openSession(execType, autoCommit));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(ExecutorType execType, TransactionIsolationLevel level) {
|
|
|
|
|
this.localSqlSession.set(openSession(execType, level));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public void startManagedSession(ExecutorType execType, Connection connection) {
|
|
|
|
|
this.localSqlSession.set(openSession(execType, connection));
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
public boolean isManagedSessionStarted() {
|
|
|
|
|
return this.localSqlSession.get() != null;
|
|
|
|
|
}
|
|
|
|
|
```
|
|
|
|
|
当需要提交/回滚事务，或关闭IocalSqlSession中记录的SqlSession对象时，需要通过SqlSessionManager的commit()、rollback()以及close()方法完成，其中会先检测当前线程是否绑定了SqlSession对象，如果未绑定则抛出异常，如果绑定了则调用该SqlSession对象的相应方法。
|
|
|
|
|
```java
|
|
|
|
|
@Override
|
|
|
|
|
public void clearCache() {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot clear the cache. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
sqlSession.clearCache();
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public void commit() {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot commit. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
sqlSession.commit();
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public void commit(boolean force) {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot commit. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
sqlSession.commit(force);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public void rollback() {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
sqlSession.rollback();
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public void rollback(boolean force) {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
sqlSession.rollback(force);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public List<BatchResult> flushStatements() {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot rollback. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
return sqlSession.flushStatements();
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
@Override
|
|
|
|
|
public void close() {
|
|
|
|
|
final SqlSession sqlSession = localSqlSession.get();
|
|
|
|
|
if (sqlSession == null) {
|
|
|
|
|
throw new SqlSessionException("Error: Cannot close. No managed session is started.");
|
|
|
|
|
}
|
|
|
|
|
try {
|
|
|
|
|
sqlSession.close();
|
|
|
|
|
} finally {
|
|
|
|
|
localSqlSession.set(null);
|
|
|
|
|
}
|
|
|
|
|
}
|
|
|
|
|
```
|
huifer
5 years ago
committed by
GitHub
