Spring Transcation注解原理解释&实践

每个事务都由拦截

org.springframework.transaction.interceptor.TransactionInterceptor

在看

org.springframework.transaction.interceptor.TransactionInterceptor.invoke(MethodInvocation)

public Object invoke(final MethodInvocation invocation) throws Throwable {
		// Work out the target class: may be {@code null}.
		// The TransactionAttributeSource should be passed the target class
		// as well as the method, which may be from an interface.
		Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return  invokeWithinTransaction(invocation.getMethod(), targetClass, new InvocationCallback() {
			@Override
			public Object proceedWithInvocation() throws Throwable {
				return invocation.proceed();
			}
		});
	}

org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(Method, Class<?>, InvocationCallback)很关键

/**
	 * General delegate for around-advice-based subclasses, delegating to several other template
	 * methods on this class. Able to handle {@link CallbackPreferringPlatformTransactionManager}
	 * as well as regular {@link PlatformTransactionManager} implementations.
	 * @param method the Method being invoked
	 * @param targetClass the target class that we're invoking the method on
	 * @param invocation the callback to use for proceeding with the target invocation
	 * @return the return value of the method, if any
	 * @throws Throwable propagated from the target invocation
	 */
	protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation)
			throws Throwable {

		// If the transaction attribute is null, the method is non-transactional.
		final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
		final PlatformTransactionManager tm = determineTransactionManager(txAttr);
		final String joinpointIdentification = methodIdentification(method, targetClass);

		if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
			// Standard transaction demarcation with getTransaction and commit/rollback calls.
			TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);//创建事务，包含事务传播机制处理和传播特性处理
			Object retVal = null;
			try {
				// This is an around advice: Invoke the next interceptor in the chain.
				// This will normally result in a target object being invoked.
				 retVal = invocation.proceedWithInvocation();//执行@Transcation标记的方法。举个例子：执行下图附件1的recharge方法 
			}
			catch (Throwable ex) {
				// target invocation exception
				 completeTransactionAfterThrowing(txInfo, ex);//recharge方法出现异常，开始回滚事务 
				throw ex;
			}
			finally {
				cleanupTransactionInfo(txInfo);
			}
			commitTransactionAfterReturning(txInfo);
			return retVal;
		}

		else {
			// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
			try {
				Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr,
						new TransactionCallback<Object>() {
							@Override
							public Object doInTransaction(TransactionStatus status) {
								TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
								try {
									return invocation.proceedWithInvocation();
								}
								catch (Throwable ex) {
									if (txAttr.rollbackOn(ex)) {
										// A RuntimeException: will lead to a rollback.
										if (ex instanceof RuntimeException) {
											throw (RuntimeException) ex;
										}
										else {
											throw new ThrowableHolderException(ex);
										}
									}
									else {
										// A normal return value: will lead to a commit.
										return new ThrowableHolder(ex);
									}
								}
								finally {
									cleanupTransactionInfo(txInfo);
								}
							}
						});

				// Check result: It might indicate a Throwable to rethrow.
				if (result instanceof ThrowableHolder) {
					throw ((ThrowableHolder) result).getThrowable();
				}
				else {
					return result;
				}
			}
			catch (ThrowableHolderException ex) {
				throw ex.getCause();
			}
		}
	}

附件1：

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———————————-分割线——————————————–

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以上晦涩难懂，综上总结如下：

spring的注解事务管理最重要的是org.springframework.jdbc.datasource.DataSourceTransactionManager

<bean id=”transactionManager”
        class=”org.springframework.jdbc.datasource.DataSourceTransactionManager”>
        <property name=”dataSource” ref=”shopDataSource” />
 </bean>

//告诉spring采用那个transactionManager处理@Transcation注解

<tx:annotation-driven transaction-manager=”transactionManager” />

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———————————-原理简化——————————————–

—————————————————————————————

       DefaultTransactionDefinition def = new DefaultTransactionDefinition();
        def.setPropagationBehavior(TransactionDefinition.PROPAGATION_REQUIRED);
        TransactionStatus status = transactionManager.getTransaction(def);
        try {
            // 1.更新订单
            result = ordersWriteDao.update(orders);
            Orders ordersDB = ordersWriteDao.get(orders.getId());
            // 2.写订单日志
            writeOrderInfo(ordersDB, sellerUser, type);

            if (updateStore) {
                // 3.更新货品和商品的库存
                this.updateProductStock(orders.getId(), false);
            }

            transactionManager.commit(status);
        } catch (Exception e) {
            log.error(“更新订单时出现未知异常：” + e);
            transactionManager.rollback(status);
            throw e;
        }