|
|
ibatis DAO 框架提供了事务管理模块。而这个事务管理可以应用到很多场合，包括JDBC、Hibernate、JTA、SQLMAP等。
下面以最简单的JDBC来分析一下其如何实现事务管理。
首先来看一段代码：
  public class OrderService  {
private DaoManager daoManager;
private OrderDao orderDao;
  public OrderService() {
daoManager = DaoConfig.getDaoManager();
orderDao = (OrderDao) daoManager.getDao(OrderDao.class);
 }
public void method() {
try {
// a separate transaction
orderDao.method1(); //第一个事务
daoManager.startTransaction(); //开始第二个事务
orderDao.method1();
orderDao.method2();
daoManager.commitTransaction();//提交第二个事务
} finally {
daoManager.endTransaction();
}
}
 }
ibatis DAO事务，有两个核心接口DaoTransactionManager和DaoTransaction
对应着不同的数据库持久层实现，两个接口分别对应着不同实现
查看ibatis 代码，可以发现这些manager实现事务，就是调用事务源的事务操作方法
JdbcDaoTransactionManager
public void commitTransaction(DaoTransaction trans) {
((JdbcDaoTransaction) trans).commit();
}
JdbcDaoTransaction
public JdbcDaoTransaction(DataSource dataSource) {
try {
connection = dataSource.getConnection();
if (connection == null) {
throw new DaoException("Could not start transaction. Cause: The DataSource returned a null connection.");
}
if (connection.getAutoCommit()) {
connection.setAutoCommit(false);
}
if (connectionLog.isDebugEnabled()) {
connection = ConnectionLogProxy.newInstance(connection);
}
} catch (SQLException e) {
throw new DaoException("Error starting JDBC transaction. Cause: " + e);
}
}
public void commit() {
try {
try {
connection.commit();
} finally {
connection.close();
}
} catch (SQLException e) {
throw new DaoException("Error committing JDBC transaction. Cause: " + e);
}
}
那么DaoTransactionManager以什么依据处理事务呢？DaoTransactionState看看DaoTransactionState的代码，非常简单，四个常量来表示事务处于的不同的状态
public static final DaoTransactionState ACTIVE = new DaoTransactionState();
public static final DaoTransactionState INACTIVE = new DaoTransactionState();
public static final DaoTransactionState COMMITTED = new DaoTransactionState();
public static final DaoTransactionState ROLLEDBACK = new DaoTransactionState(); 那么实际程序中是如何控制事务的呢
在第一段代码中，我们是这样取得DAO
orderDao = (OrderDao) daoManager.getDao(OrderDao.class);
实际daoManager返回的并不是orderDao的具体实现类，它返回的DaoProxy
DaoProxy
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Object result = null;
if (PASSTHROUGH_METHODS.contains(method.getName())) {
try {
result = method.invoke(daoImpl.getDaoInstance(), args);
} catch (Throwable t) {
throw ClassInfo.unwrapThrowable(t);
}
} else {
StandardDaoManager daoManager = daoImpl.getDaoManager();
DaoContext context = daoImpl.getDaoContext();
if (daoManager.isExplicitTransaction()) {
// Just start the transaction (explicit)
try {
context.startTransaction();
result = method.invoke(daoImpl.getDaoInstance(), args);
} catch (Throwable t) {
throw ClassInfo.unwrapThrowable(t);
}
} else {
// Start, commit and end the transaction (autocommit)
try {
context.startTransaction();
result = method.invoke(daoImpl.getDaoInstance(), args);
context.commitTransaction();
} catch (Throwable t) {
throw ClassInfo.unwrapThrowable(t);
} finally {
context.endTransaction();
}
}
}
return result;
} 看到这段代码就非常清楚了，每调用DAO的一次方法时，如果不显式的调用daoManager.startTransaction()，就会成为单独的一个事务。再看看ibatis为我们提供的摸板JdbcDaoTemplate
protected Connection getConnection() {
DaoTransaction trans = daoManager.getTransaction(this);
if (!(trans instanceof ConnectionDaoTransaction)) {
throw new DaoException("The DAO manager of type " + daoManager.getClass().getName() +
" cannot supply a JDBC Connection for this template, and is therefore not" +
"supported by JdbcDaoTemplate.");
}
return ((ConnectionDaoTransaction) trans).getConnection();
}
ibatis控制多个DAO的事务实际是让这些DAO共用了一个DaoTransaction（ThreadLocal），一个Connection
这里是一个事务源的情况，如果多个事务源之间要完成全局事务，还是老老实实用分布式事务管理服务吧（jta）
|
|
|
|
您现在的位置： 
网友评论：（最新10条。只代表网友观点，与本站立场无关！）
