本地事务系列之三：使用TransactionTemplate

TransactionTemplate的灵活性好，可以给代码块加事务处理，而不是方法粒度的控制。

FruitShop实现：

public class TxTemplateJdbcFruitShop extends JdbcDaoSupport implements FruitShop {
	private PlatformTransactionManager txManager;

	public void setTxManager(PlatformTransactionManager txManager) {
		this.txManager = txManager;
	}

	@Override
	public boolean purchase(final int fruitId, final String userName, final int count) {
		TransactionTemplate txTemplate = new TransactionTemplate(txManager);
		
		final String querySql = "SELECT PRICE FROM FRUIT WHERE ID = ?";
		final String upStockSql = "UPDATE FRUIT_STOCK SET STOCK = STOCK - ? WHERE ID = ?";
		final String upAccountSql = "UPDATE ACCOUNT SET BALANCE = BALANCE - ? WHERE USERNAME = ?";

		int retVal = txTemplate.execute(new TransactionCallback<Integer>() {

			@Override
			public Integer doInTransaction(TransactionStatus status) {
				int price = getJdbcTemplate().queryForInt(querySql, new Object[] { fruitId });
				getJdbcTemplate().update(upStockSql, new Object[] { count, fruitId });
				getJdbcTemplate().update(upAccountSql, new Object[] { price * count, userName });
				return 1;
			}
		});

		return retVal == 1;
	}
}

beans-fruitshop.xml文件加入：

<bean id="txTemplateFruitShop" class="com.john.tx.service.impl.TxTemplateJdbcFruitShop">
  <property name="dataSource" ref="dataSource" />
  <property name="txManager" ref="txManager" />
</bean>

JdbcFruitShopTest类加入：

@Resource(name = "txTemplateFruitShop")
FruitShop txTemplateFruitShop;

@Test
public void txTemplateTest() {
	int fruitId = 1;
	String userName = "user1";
	int count = 3;
	txTemplateFruitShop.purchase(fruitId, userName, count);
}

附：
1. 可以直接注入TransactionTemplate实例，不用在代码中实例化：
去除PlatformTransactionManager属性，直接使用TransactionTemplate属性：

private TransactionTemplate txTemplate;

public void setTxTemplate(TransactionTemplate txTemplate) {
	this.txTemplate = txTemplate;
}

beans-fruitshop.xml加入：

<bean id="txTemplate" class="org.springframework.transaction.support.TransactionTemplate">
  <property name="transactionManager" ref="txManager" />
</bean>

<bean id="txTemplateFruitShop" class="com.john.tx.service.impl.TxTemplateJdbcFruitShop">
  <property name="dataSource" ref="dataSource" />
  <property name="txTemplate" ref="txTemplate" />
</bean>

2. execute方法可以接受TransactionCallback接口的抽象类，如TransactionCallbackWithoutResult：

txTemplate.execute(new TransactionCallbackWithoutResult() {

	@Override
	protected void doInTransactionWithoutResult(TransactionStatus status) {
		...
	}
});

看下其实现：
接口方法中抽出一个没有返回结果的抽象方法（由用户自己实现），返回null是为了适配接口。

public abstract class TransactionCallbackWithoutResult implements TransactionCallback<Object> {
	public final Object doInTransaction(TransactionStatus status) {
		doInTransactionWithoutResult(status);
		return null; // 返回null
	}

	// 抽象方法，需要自定义实现
	protected abstract void doInTransactionWithoutResult(TransactionStatus status);
}