事务注解@Transactional及其属性
Transactional的属性：
| 属性名称 | 功能描述 | 默认值 |
|---|---|---|
| transactionManager（value的别名） | 指定事务管理器 | ”“ |
| value | 指定事务管理器 | ”“ |
| propagation | 事务的传播行为，规定事务方法相互调用的时候的解决方法 | Propagation.REQUIRED |
| isolation | 事务的隔离级别 | Isolation.DEFAULT |
| timeout | 事务的超时时，如果超过该时间限制但事务还没有完成，则自动回滚事务 | -1 |
| readOnly | 指定事务是否为只读事务，声明只读可加快事务执行速度 | false |
| rollbackFor | 抛出指定的异常类型，不回滚事务 | {}(空） |
| noRollbackFor | 用于指定能够触发事务回滚的异常类型，可以指定多个异常类型 | {}(空） |
| rollbackForClassName | 设置需要进行回滚的异常类名称数组，当方法中抛出指定异常名称数组中的异常时，则进行事务回滚 | {}(空） |
| noRollbackForClassName | 不需要进行回滚的异常类名称数组，当方法中抛出指定异常名称数组中的异常时，不进行事务回滚 | {}(空） |
propagation类型
规定多个事务方法之前存在相互调用时如何实现事务
isolation类型
注解源码
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface Transactional {
/**
* Alias for {@link #transactionManager}.
* @see #transactionManager
*/
@AliasFor("transactionManager")
String value() default "";
/**
* A <em>qualifier</em> value for the specified transaction.
* <p>May be used to determine the target transaction manager, matching the
* qualifier value (or the bean name) of a specific
* {@link org.springframework.transaction.TransactionManager TransactionManager}
* bean definition.
* @since 4.2
* @see #value
* @see org.springframework.transaction.PlatformTransactionManager
* @see org.springframework.transaction.ReactiveTransactionManager
*/
@AliasFor("value")
String transactionManager() default "";
/**
* The transaction propagation type.
* <p>Defaults to {@link Propagation#REQUIRED}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getPropagationBehavior()
*/
Propagation propagation() default Propagation.REQUIRED;
/**
* The transaction isolation level.
* <p>Defaults to {@link Isolation#DEFAULT}.
* <p>Exclusively designed for use with {@link Propagation#REQUIRED} or
* {@link Propagation#REQUIRES_NEW} since it only applies to newly started
* transactions. Consider switching the "validateExistingTransactions" flag to
* "true" on your transaction manager if you'd like isolation level declarations
* to get rejected when participating in an existing transaction with a different
* isolation level.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getIsolationLevel()
* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setValidateExistingTransaction
*/
Isolation isolation() default Isolation.DEFAULT;
/**
* The timeout for this transaction (in seconds).
* <p>Defaults to the default timeout of the underlying transaction system.
* <p>Exclusively designed for use with {@link Propagation#REQUIRED} or
* {@link Propagation#REQUIRES_NEW} since it only applies to newly started
* transactions.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getTimeout()
*/
int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
/**
* A boolean flag that can be set to {@code true} if the transaction is
* effectively read-only, allowing for corresponding optimizations at runtime.
* <p>Defaults to {@code false}.
* <p>This just serves as a hint for the actual transaction subsystem;
* it will <i>not necessarily</i> cause failure of write access attempts.
* A transaction manager which cannot interpret the read-only hint will
* <i>not</i> throw an exception when asked for a read-only transaction
* but rather silently ignore the hint.
* @see org.springframework.transaction.interceptor.TransactionAttribute#isReadOnly()
* @see org.springframework.transaction.support.TransactionSynchronizationManager#isCurrentTransactionReadOnly()
*/
boolean readOnly() default false;
/**
* Defines zero (0) or more exception {@link Class classes}, which must be
* subclasses of {@link Throwable}, indicating which exception types must cause
* a transaction rollback.
* <p>By default, a transaction will be rolling back on {@link RuntimeException}
* and {@link Error} but not on checked exceptions (business exceptions). See
* {@link org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn(Throwable)}
* for a detailed explanation.
* <p>This is the preferred way to construct a rollback rule (in contrast to
* {@link #rollbackForClassName}), matching the exception class and its subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(Class clazz)}.
* @see #rollbackForClassName
* @see org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn(Throwable)
*/
Class<? extends Throwable>[] rollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}), indicating which exception types must cause
* a transaction rollback.
* <p>This can be a substring of a fully qualified class name, with no wildcard
* support at present. For example, a value of {@code "ServletException"} would
* match {@code javax.servlet.ServletException} and its subclasses.
* <p><b>NB:</b> Consider carefully how specific the pattern is and whether
* to include package information (which isn't mandatory). For example,
* {@code "Exception"} will match nearly anything and will probably hide other
* rules. {@code "java.lang.Exception"} would be correct if {@code "Exception"}
* were meant to define a rule for all checked exceptions. With more unusual
* {@link Exception} names such as {@code "BaseBusinessException"} there is no
* need to use a FQN.
* <p>Similar to {@link org.springframework.transaction.interceptor.RollbackRuleAttribute#RollbackRuleAttribute(String exceptionName)}.
* @see #rollbackFor
* @see org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn(Throwable)
*/
String[] rollbackForClassName() default {};
/**
* Defines zero (0) or more exception {@link Class Classes}, which must be
* subclasses of {@link Throwable}, indicating which exception types must
* <b>not</b> cause a transaction rollback.
* <p>This is the preferred way to construct a rollback rule (in contrast
* to {@link #noRollbackForClassName}), matching the exception class and
* its subclasses.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(Class clazz)}.
* @see #noRollbackForClassName
* @see org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn(Throwable)
*/
Class<? extends Throwable>[] noRollbackFor() default {};
/**
* Defines zero (0) or more exception names (for exceptions which must be a
* subclass of {@link Throwable}) indicating which exception types must <b>not</b>
* cause a transaction rollback.
* <p>See the description of {@link #rollbackForClassName} for further
* information on how the specified names are treated.
* <p>Similar to {@link org.springframework.transaction.interceptor.NoRollbackRuleAttribute#NoRollbackRuleAttribute(String exceptionName)}.
* @see #noRollbackFor
* @see org.springframework.transaction.interceptor.DefaultTransactionAttribute#rollbackOn(Throwable)
*/
String[] noRollbackForClassName() default {};
}
事务的实现原理
Spring 中支持两种事务处理的方式，分别是声明式事务处理与编程式事务处理，两者相对于开发人员来讲差别很大，但是对于Spring 中的实现来讲，大同小异。核心原理都是通过拦截器来实现的，TransactionInterceptor 支撑着整个事务功能的架构。TransactionInterceptor类继承自 MethodInterceptor，所以调用该类是从其 invoke 方法开始的：
@Override
@Nullable
public Object invoke(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, 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();
//1.获取事务属性
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
//2. 加载配置中配置的 TransactionManager
final TransactionManager tm = determineTransactionManager(txAttr);
if (this.reactiveAdapterRegistry != null && tm instanceof ReactiveTransactionManager) {
ReactiveTransactionSupport txSupport = this.transactionSupportCache.computeIfAbsent(method, key -> {
if (KotlinDetector.isKotlinType(method.getDeclaringClass()) && KotlinDelegate.isSuspend(method)) {
throw new TransactionUsageException(
"Unsupported annotated transaction on suspending function detected: " + method +
". Use TransactionalOperator.transactional extensions instead.");
}
ReactiveAdapter adapter = this.reactiveAdapterRegistry.getAdapter(method.getReturnType());
if (adapter == null) {
throw new IllegalStateException("Cannot apply reactive transaction to non-reactive return type: " +
method.getReturnType());
}
return new ReactiveTransactionSupport(adapter);
});
return txSupport.invokeWithinTransaction(
method, targetClass, invocation, txAttr, (ReactiveTransactionManager) tm);
}
PlatformTransactionManager ptm = asPlatformTransactionManager(tm);
////构造方法唯一标识（类.方法，如 service.UserServiceImpl.save）
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
//声明式事务处理
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
//创建TransactionInfo
TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
//执行被增强方法
retVal = invocation.proceedWithInvocation();
} catch (Throwable ex) {
// target invocation exception
//异常回滚
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
} finally {
//清除信息
cleanupTransactionInfo(txInfo);
}
if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
TransactionStatus status = txInfo.getTransactionStatus();
if (status != null && txAttr != null) {
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
}
//提交事务
commitTransactionAfterReturning(txInfo);
return retVal;
}
//编程式事务处理
else {
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
Object result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
try {
Object retVal = invocation.proceedWithInvocation();
if (vavrPresent && VavrDelegate.isVavrTry(retVal)) {
// Set rollback-only in case of Vavr failure matching our rollback rules...
retVal = VavrDelegate.evaluateTryFailure(retVal, txAttr, status);
}
return retVal;
} 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;
}
}
}
在 invoke 中我们也可以看到这两种方式的实现。考虑到对事务的应用声明式的事务比编程式处理使用起来方便，也相对流行些，我们就以此种方式进行分析。对于声明式的事务处理主要有以下几个步骤。
- 获取事务的属性。对于事务处理来说，最基础或者说最首要的工作便是获取事务属性了，这是支撑整个事务功能的基石，如果没有事务属性，其他功能也无从谈起
- 加载配置中配置的 TransactionManager
- 不同的事务处理方式使用不同的逻辑。对于声明式事务的处理与编程式事务的处理，第一点区别在于事务属性上，因为编程式的事务处理是不需要有事务属性的，第二点区别就是在 TransactionManager上，CallbackPreferring PlatformTransactionManager 实现 PlatformTransactionManager 接口，暴露出一个方法用于执行事务处理中的回调。所以，这两种方式都可以用作事务处理方式的判断。
- 在目标方法执行前获取事务并收集事务信息。事务信息与事务属性并不相同，也就是 TransactionInfo 与 TransactionAttribute 并不相同，TransactionInfo 中包含 TransactionAttribute 信息，但是，除了 TransactionAttribute 外还有其他事务信息，例如 PlatformTransactionManager 以及 TransactionStatus相关信息。
- 执行目标方法。
- 一旦出现异常，尝试异常处理。并不是所有异常，Spring都会将其回滚，默认只对 RuntimeException 回滚。
- 提交事务前的事务信息清除。
- 提交事务。 【参考】
【1】《Spring源码深度解析》
