引言
SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
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| try (SqlSession session = sqlSessionFactory.openSession()) {
Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);
}
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上面是官方文档的内容：MyBatis官方文档|入门
在上一篇文章分析MyBatis执行SQL的时候，遗留了一些关于SqlSession的疑问，怎么创建，怎么释放。
SqlSessionTemplate的SqlSessionInterceptor中解决了上面的疑问：
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| @Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
SqlSession sqlSession = getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
try {
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
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1、SqlSession的创建
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public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {
notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);
SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
SqlSession session = sessionHolder(executorType, holder);
if (session != null) {
return session;
}
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Creating a new SqlSession");
}
session = sessionFactory.openSession(executorType);
registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);
return session;
}
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SqlSessionUtils中的方法，首先从SqlSessionHolder中获取SqlSession，如果获取失败，则创建一个新的。
这里着重看sessionFactory.openSession(executorType),DefaultSqlSessionFactory：
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| private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
Transaction tx = null;
try {
final Environment environment = configuration.getEnvironment();
final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
final Executor executor = configuration.newExecutor(tx, execType);
return new DefaultSqlSession(configuration, executor, autoCommit);
} catch (Exception e) {
closeTransaction(tx);
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
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方法入参：execType为SIMPLE,level为null，autoCommit为false。
首先获取Environment，在获取TransactionFactory，之后获取Transaction和Executor，最后返回DefaultSqlSession。
1.1、获取的TransactionFactory是什么时候设置的
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| private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
if (environment == null || environment.getTransactionFactory() == null) {
return new ManagedTransactionFactory();
}
return environment.getTransactionFactory();
}
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如果未配置TransactionFactory，则返回ManagedTransactionFactory，否则返回配置的TransactionFactory。
什么时候配置的呢？在分析SqlSessionFactoryBean的创建时有一段代码：
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| if (this.transactionFactory == null) {
this.transactionFactory = new SpringManagedTransactionFactory();
}
configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));
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即默认使用的是SpringManagedTransactionFactory。
1.2、newTransaction
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| public Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit) {
return new SpringManagedTransaction(dataSource);
}
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新建事务，这里DataSource为手动配置的com.zaxxer.hikari.HikariDataSource。另外两个参数没有使用，都是使用的数据源配置
1.3、newExecutor
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| public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
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) {
executor = new CachingExecutor(executor);
}
executor = (Executor) interceptorChain.pluginAll(executor);
return executor;
}
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新建SQL执行器,因为我的例子是SimpleExecutor，且使用了缓存，所以最后返回的是CachingExecutor，使用了装饰者模式。
2、SqlSession的关闭
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public static void closeSqlSession(SqlSession session, SqlSessionFactory sessionFactory) {
notNull(session, NO_SQL_SESSION_SPECIFIED);
notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
if ((holder != null) && (holder.getSqlSession() == session)) {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Releasing transactional SqlSession [" + session + "]");
}
holder.released();
} else {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Closing non transactional SqlSession [" + session + "]");
}
session.close();
}
}
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