④ 事务回滚原理

在前文单测类注入中我们知道.JUnit提供了一些监听器,允许当单测方法执行时候去对单测上下文进行调整。所以呢事务回滚也是基于这里的特性完成的。基于SpringBoot 2.1.x版本分析

源码分析#

Spring中为了适配不通的数据库,提供了事务平台的概念。 PlatformTransactionManager 只要实现了该接口就允许对事务进行控制。具体事务的控制是通过工具类来处理的。 TransactionContextHolder 可以获取当前线程执行的事务上下文。JUnit通过该工具拿到事务的上下文,然后对此做响应的修改。具体的修改逻辑见下文注释。两句话解释清楚。

TransactionalTestExecutionListener

伪代码分析

    // 单测方法执行前,移除容器原来的事务管理器,然后开启一个新的事务
    @Override
    public void beforeTestMethod(final TestContext testContext) throws Exception {
        Method testMethod = testContext.getTestMethod();
        Class<?> testClass = testContext.getTestClass();
        Assert.notNull(testMethod, "Test method of supplied TestContext must not be null");

        TransactionContext txContext = TransactionContextHolder.removeCurrentTransactionContext();
        Assert.state(txContext == null, "Cannot start new transaction without ending existing transaction");

        PlatformTransactionManager tm = null;
        TransactionAttribute transactionAttribute = this.attributeSource.getTransactionAttribute(testMethod, testClass);

        if (transactionAttribute != null) {
            transactionAttribute = TestContextTransactionUtils.createDelegatingTransactionAttribute(testContext,
                transactionAttribute);

            if (logger.isDebugEnabled()) {
                logger.debug("Explicit transaction definition [" + transactionAttribute +
                        "] found for test context " + testContext);
            }

            if (transactionAttribute.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
                return;
            }

            tm = getTransactionManager(testContext, transactionAttribute.getQualifier());
            Assert.state(tm != null,
                    () -> "Failed to retrieve PlatformTransactionManager for @Transactional test: " + testContext);
        }

        if (tm != null) {
            txContext = new TransactionContext(testContext, tm, transactionAttribute, isRollback(testContext));
            runBeforeTransactionMethods(testContext);
            txContext.startTransaction();
            TransactionContextHolder.setCurrentTransactionContext(txContext);
        }
    }
    
    // 单测方法执行结束后,结束事务然后回滚或提交
    @Override
    public void afterTestMethod(TestContext testContext) throws Exception {
        Method testMethod = testContext.getTestMethod();
        Assert.notNull(testMethod, "The test method of the supplied TestContext must not be null");

        TransactionContext txContext = TransactionContextHolder.removeCurrentTransactionContext();
        // If there was (or perhaps still is) a transaction...
        if (txContext != null) {
            TransactionStatus transactionStatus = txContext.getTransactionStatus();
            try {
                // If the transaction is still active...
                if (transactionStatus != null && !transactionStatus.isCompleted()) {
                    txContext.endTransaction();
                }
            }
            finally {
                runAfterTransactionMethods(testContext);
            }
        }
    }