在上一篇文章我们已经得到了DefaultSqlSessionFactory
@Override
public SqlSession openSession() {
return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}
在configuration内部默认指定了protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
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); // may have fetched a connection so lets call close()
throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
从代码中我们可知开启了一个jdbc事务，并调用newExecutor得到一个执行期
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;
}
如果开启了cache，那么会得到一个CachingExecutor，这采用的是装饰设计模式，它的语句执行实际是交给内部的delegate来执行的。
里面值得注意的是使用了(Executor) interceptorChain.pluginAll(executor)将所有的拦截器注入进去形成一个拦截链。
public Object pluginAll(Object target) {
for (Interceptor interceptor : interceptors) {
target = interceptor.plugin(target);
}
return target;
}
@Override
public Object plugin(Object target) {
return Plugin.wrap(target, this);
}
其实Plugin是mybatis的一个工具类，用来方便生成代理对象的，注意这个地方只会生成拦截目标是Executor的拦截类的代理对象，如下所示这种就不会调用。
@Intercepts({
@Signature(type = StatementHandler.class,
method = "prepare",
args = {Connection.class})
})
然后返回DefaultSqlSession的一个实例对象
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
至此DefaultSqlSessionFactory创建DefaultSqlSession的过程完成。
