spring事务入口及核心类-基于spring5.1.9版本

public interface PlatformTransactionManager {
	TransactionStatus getTransaction(@Nullable TransactionDefinition definition)
			throws TransactionException;		
	void commit(TransactionStatus status) throws TransactionException;		
	void rollback(TransactionStatus status) throws TransactionException;

}

public interface TransactionDefinition {
    int PROPAGATION_REQUIRED = 0;
    int PROPAGATION_SUPPORTS = 1;
    int PROPAGATION_MANDATORY = 2;
    int PROPAGATION_REQUIRES_NEW = 3;
    int PROPAGATION_NOT_SUPPORTED = 4;
    int PROPAGATION_NEVER = 5;
    int PROPAGATION_NESTED = 6;
    int ISOLATION_DEFAULT = -1;
    int ISOLATION_READ_UNCOMMITTED = Connection.TRANSACTION_READ_UNCOMMITTED;
    int ISOLATION_READ_COMMITTED = Connection.TRANSACTION_READ_COMMITTED;
    int ISOLATION_REPEATABLE_READ = Connection.TRANSACTION_REPEATABLE_READ;
    int ISOLATION_SERIALIZABLE = Connection.TRANSACTION_SERIALIZABLE;
    int TIMEOUT_DEFAULT = -1;
    
    int getPropagationBehavior();
    int getIsolationLevel();
    int getTimeout();
    boolean isReadOnly();
    String getName();
}    

public interface TransactionStatus extends SavepointManager, Flushable {
    boolean isNewTransaction();
    boolean hasSavepoint();
    void setRollbackOnly();
    boolean isRollbackOnly();
    void flush();
    boolean isCompleted();
}   

public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean {
  //用于存储默认事务管理器的键。  
  private static final Object DEFAULT_TRANSACTION_MANAGER_KEY = new Object();
    //currentTransactionStatus的持有者
  private static final ThreadLocal<TransactionInfo> transactionInfoHolder =
			new NamedThreadLocal<>("Current aspect-driven transaction"); 
    
  //获取当前事务信息  
  protected static TransactionInfo currentTransactionInfo() throws NoTransactionException {
		return transactionInfoHolder.get();
	}  
    
    // ..............................
}    

public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
    // ...................................  省略其他代码
    
    public Object invoke(MethodInvocation invocation) throws Throwable {

		// 获取目标class
		Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);

		// Adapt to TransactionAspectSupport's invokeWithinTransaction...
		return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
	}
    
    protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
			final InvocationCallback invocation) throws Throwable {

		// If the transaction attribute is null, the method is non-transactional.
		TransactionAttributeSource tas = getTransactionAttributeSource();
        //查询目标方法事务属性、确定事务管理器、构造连接点标识（用于确认事务名称）
		final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
		final PlatformTransactionManager tm = determineTransactionManager(txAttr);
		final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

		if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
			// 获取事务
			TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);

			Object retVal;
			try {

				//通过回调执行目标方法
				retVal = invocation.proceedWithInvocation();
			}
			catch (Throwable ex) {
				// target invocation exception
				completeTransactionAfterThrowing(txInfo, ex);
				throw ex;
			}
			finally {
                //清理当前线程事务信息
				cleanupTransactionInfo(txInfo);
			}
            //目标方法执行成功，提交事务
			commitTransactionAfterReturning(txInfo);
			return retVal;
		}

		else {
			final ThrowableHolder throwableHolder = new ThrowableHolder();

			// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in. 回调的事务执行处理
			try {
				Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr, 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.
							throwableHolder.throwable = ex;
							return null;
						}
					}
					finally {
						cleanupTransactionInfo(txInfo);
					}
				});

				// Check result state: It might indicate a Throwable to rethrow.
				if (throwableHolder.throwable != null) {
					throw throwableHolder.throwable;
				}
				return result;
			}
			catch (ThrowableHolderException ex) {
				throw ex.getCause();
			}
			catch (TransactionSystemException ex2) {
				if (throwableHolder.throwable != null) {
					logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
					ex2.initApplicationException(throwableHolder.throwable);
				}
				throw ex2;
			}
			catch (Throwable ex2) {
				if (throwableHolder.throwable != null) {
					logger.error("Application exception overridden by commit exception", throwableHolder.throwable);
				}
				throw ex2;
			}
		}
	}
 
    // ...................................   
}

public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
    Object transaction = doGetTransaction();
    // 参数为null时构造默认值
    ...
    if (isExistingTransaction(transaction)) {
        // Existing transaction found -> check propagation behavior to find out how to behave.
        return handleExistingTransaction(definition, transaction, debugEnabled);
    }
    ...

// 获取当前事务对象
protected abstract Object doGetTransaction() throws TransactionException;

// 判断当前事务对象是否包含活跃事务
protected boolean isExistingTransaction(Object transaction) throws TransactionException {
    return false;
}

// DataSourceTransactionManager.class
@Override
protected Object doGetTransaction() {
    DataSourceTransactionObject txObject = new DataSourceTransactionObject();
    txObject.setSavepointAllowed(isNestedTransactionAllowed());
    ConnectionHolder conHolder =
            (ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
    txObject.setConnectionHolder(conHolder, false);
    return txObject;
}

@Override
protected boolean isExistingTransaction(Object transaction) {
    DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
    return (txObject.hasConnectionHolder() && txObject.getConnectionHolder().isTransactionActive());
}

// AbstractPlatformTransactionManager.class
private void processCommit(DefaultTransactionStatus status) throws TransactionException {
    try {
        boolean beforeCompletionInvoked = false;
        try {
            prepareForCommit(status);
            triggerBeforeCommit(status);
            triggerBeforeCompletion(status);
            ....
            else if (status.isNewTransaction()) {
                // 记录日志
                ...
                doCommit(status);
            }
            ...
        // 事务调用异常处理
        ...
        try {
            triggerAfterCommit(status);
        }
        finally {
            triggerAfterCompletion(status, TransactionSynchronization.STATUS_COMMITTED);
        }
    }
}

TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
    @Override
    public void afterCommit() {
        // do something after commit
    }
});