JFinal 源码导读第七天(1) @Before(Tx.class)

1.这里是单独的介绍事物

/**
 * ActiveRecord declare transaction.
 * Example: @Before(Tx.class)
 */
public class Tx implements Interceptor {
	
	protected int getTransactionLevel() {
		return DbKit.getTransactionLevel();
	}
	
	public void intercept(ActionInvocation invocation) {
		Connection conn = DbKit.getThreadLocalConnection();
		if (conn != null) {	// Nested transaction support
			try {
				if (conn.getTransactionIsolation() < getTransactionLevel())
					conn.setTransactionIsolation(getTransactionLevel());
				invocation.invoke();
				return ;
			} catch (SQLException e) {
				throw new ActiveRecordException(e);
			}
		}
		
		Boolean autoCommit = null;
		try {
			conn = DbKit.getConnection();
			autoCommit = conn.getAutoCommit();
			DbKit.setThreadLocalConnection(conn);
			conn.setTransactionIsolation(getTransactionLevel());	// conn.setTransactionIsolation(transactionLevel);
			conn.setAutoCommit(false);
			invocation.invoke();
			conn.commit();
		} catch (Exception e) {
			if (conn != null)
				try {conn.rollback();} catch (Exception e1) {e1.printStackTrace();}
			throw new ActiveRecordException(e);
		}
		finally {
			try {
				if (conn != null) {
					if (autoCommit != null)
						conn.setAutoCommit(autoCommit);
					conn.close();
				}
			} catch (Exception e) {
				e.printStackTrace();	// can not throw exception here, otherwise the more important exception in previous catch block can not be thrown
			}
			finally {
				DbKit.removeThreadLocalConnection();	// prevent memory leak
			}
		}
	}
}

2.如果我们在Controller的类和Controller的方法中都定义啦@Before(Tx.class)事物
1 .假如是第一次进入该方法在类上面定义的
2.Connection conn = DbKit.getThreadLocalConnection();

/**
	 * Helps to implement nested transaction.
	 * Tx.intercept(...) and Db.tx(...) need this method to detected if it in nested transaction.
	 */
	public static final Connection getThreadLocalConnection() {
		return threadLocal.get();
	}

3.threadLocal.get()肯定是为null,这个方法主要是嵌套事物,什么是嵌套事物,我下面有个链接,自己看看吧
http://www.iteye.com/topic/35907
4.conn = DbKit.getConnection(); 获取到当前的连接

/**
	 * Get Connection. Support transaction if Connection in ThreadLocal
	 */
	public static final Connection getConnection() throws SQLException {
		Connection conn = threadLocal.get();
		if (conn != null)
			return conn;
		return showSql ? new SqlReporter(dataSource.getConnection()).getConnection() : dataSource.getConnection();
	}

5.DbKit.setThreadLocalConnection(conn);将当前的conn连接保存到thread当中去
6.conn.setTransactionIsolation(getTransactionLevel()); 设置当前conn的事物级别
7.conn.setAutoCommit(false); 关键让自动提交为false
8.invocation.invoke(); 调用下一个拦截器
9.conn.commit(); 事物提交
10.try {conn.rollback();} catch (Exception e1) {e1.printStackTrace();} 如果发送异常,事物要回滚

3..假如第二次进入的是该方法的定义上面的事物拦截器
1.Connection conn = DbKit.getThreadLocalConnection();
那么第二次进入该方法,conn不会空

if (conn.getTransactionIsolation() < getTransactionLevel())				
conn.setTransactionIsolation(getTransactionLevel());

这行代码非常简单,就是conn的事物级别小于我们定义的事物级别,就设计conn的事物级别为我们默认的事物级别
invocation.invoke();调用下一个拦截器
假如调用过程中发生了异常,内部事物就抛出了异常

throw new ActiveRecordException(e);

4.嵌套事物是和外部事物一起提交生效,你想想拦截器的过程就明白啦