前面的章节主要讲mybatis如何解析配置文件，这些都是一次性的过程。从本章开始讲解动态的过程，它们跟应用程序对mybatis的调用密切相关。本章先从sqlsession开始。
创建
正如其名，Sqlsession对应着一次
数据库会话。由于数据库回话不是永久的，因此Sqlsession的生命周期也不应该是永久的，相反，在你每次访问数据库时都需要创建它（当然并不是说在Sqlsession里只能执行一次sql，你可以执行多次，当一旦关闭了Sqlsession就需要重新创建它）。创建Sqlsession的地方只有一个，那就是SqlsessionFactory的openSession方法：
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public SqlSessionopenSession() { returnopenSessionFromDataSource(configuration.getDefaultExecutorType(),null, false);
}
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private SqlSessionopenSessionFromDataSource(ExecutorType execType, TransactionIsolationLevellevel, boolean autoCommit) {
Connectionconnection = null;
try {
finalEnvironment environment = configuration.getEnvironment();
final DataSourcedataSource = getDataSourceFromEnvironment(environment);
TransactionFactory transactionFactory =getTransactionFactoryFromEnvironment(environment);
connection = dataSource.getConnection();
if (level != null) {
connection.setTransactionIsolation(level.getLevel());
}
connection = wrapConnection(connection);
Transaction tx = transactionFactory.newTransaction(connection,autoCommit);
Executorexecutor = configuration.newExecutor(tx, execType);
returnnewDefaultSqlSession(configuration, executor, autoCommit);
} catch (Exceptione) {
closeConnection(connection);
throwExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
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public ExecutornewExecutor(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);
} elseif(ExecutorType.REUSE == executorType) { executor = new ReuseExecutor(this,transaction);
} else { executor = newSimpleExecutor(this, transaction);
}
if (cacheEnabled) { executor = new CachingExecutor(executor);
} executor =(Executor) interceptorChain.pluginAll(executor);
return executor; }
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session = sqlSessionFactory.openSession(); UserDao userDao= session.getMapper(UserDao.class);
UserDto user =new UserDto(); user.setUsername("iMbatis");
user.setPassword("iMbatis"); userDao.insertUser(user);
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public T getMapper(Class type, SqlSession sqlSession) { if (!knownMappers.contains(type))
thrownewBindingException("Type " + type + " isnot known to the MapperRegistry."); try {
returnMapperProxy.newMapperProxy(type, sqlSession); } catch (Exceptione) {
thrownewBindingException("Error getting mapper instance. Cause: " + e, e); }
}
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publicstatic T newMapperProxy(Class mapperInterface, SqlSession sqlSession) { ClassLoaderclassLoader = mapperInterface.getClassLoader();
Class[] interfaces = new Class[]{mapperInterface}; MapperProxyproxy = new MapperProxy(sqlSession);
return (T) Proxy.newProxyInstance(classLoader,interfaces, proxy); }
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public Objectinvoke(Object proxy, Method method, Object[] args) throws Throwable{ if (method.getDeclaringClass()== Object.class) {