O princípio de realização da transação Springboot
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A implementação de transações do Spring é dividida em programática e declarativa. A declarativa é a mais comum. A implementação de transações declarativas é dividida em arquivos de configuração XML e anotações @Transactional. SpringBoot cancela a gravação de arquivos de configuração XML. Portanto, a transação em SpringBoot é principalmente realizado usando a anotação @Transactional. O princípio é analisado abaixo do ponto de vista do código-fonte
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É sabido que o princípio de implementação da transação @Transactional é baseado em AOP. No blog anterior, o princípio de realização de AOP foi explicado em detalhes: proxy dinâmico + cadeia de interceptação. A partir disso, podemos inferir aproximadamente a lógica de implementação de @Transactional : Spring tem um interceptor de realçador (interceptor) alvo @ Transactional, na última etapa da inicialização da instância de bean, a cadeia de interceptor com o interceptor será chamada para aprimorar o método de anotação @Transactional, e a classe proxy será gerada
Anotação @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.PlatformTransactionManager}
* bean definition.
* @since 4.2
* @see #value
*/
@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}.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getIsolationLevel()
*/
Isolation isolation() default Isolation.DEFAULT;
/**
* The timeout for this transaction.
* <p>Defaults to the default timeout of the underlying transaction system.
* @see org.springframework.transaction.interceptor.TransactionAttribute#getTimeout()
*/
int timeout() default TransactionDefinition.TIMEOUT_DEFAULT;
/**
* {@code true} if the transaction is read-only.
* <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()
*/
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 {
};
Nível de isolamento de transação
/**
* Use the default isolation level of the underlying datastore.
* All other levels correspond to the JDBC isolation levels.
* @see java.sql.Connection
*/
DEFAULT(TransactionDefinition.ISOLATION_DEFAULT),
/**
* A constant indicating that dirty reads, non-repeatable reads and phantom reads
* can occur. This level allows a row changed by one transaction to be read by
* another transaction before any changes in that row have been committed
* (a "dirty read"). If any of the changes are rolled back, the second
* transaction will have retrieved an invalid row.
* @see java.sql.Connection#TRANSACTION_READ_UNCOMMITTED
*/
READ_UNCOMMITTED(TransactionDefinition.ISOLATION_READ_UNCOMMITTED),
/**
* A constant indicating that dirty reads are prevented; non-repeatable reads
* and phantom reads can occur. This level only prohibits a transaction
* from reading a row with uncommitted changes in it.
* @see java.sql.Connection#TRANSACTION_READ_COMMITTED
*/
READ_COMMITTED(TransactionDefinition.ISOLATION_READ_COMMITTED),
/**
* A constant indicating that dirty reads and non-repeatable reads are
* prevented; phantom reads can occur. This level prohibits a transaction
* from reading a row with uncommitted changes in it, and it also prohibits
* the situation where one transaction reads a row, a second transaction
* alters the row, and the first transaction rereads the row, getting
* different values the second time (a "non-repeatable read").
* @see java.sql.Connection#TRANSACTION_REPEATABLE_READ
*/
REPEATABLE_READ(TransactionDefinition.ISOLATION_REPEATABLE_READ),
/**
* A constant indicating that dirty reads, non-repeatable reads and phantom
* reads are prevented. This level includes the prohibitions in
* {@code ISOLATION_REPEATABLE_READ} and further prohibits the situation
* where one transaction reads all rows that satisfy a {@code WHERE}
* condition, a second transaction inserts a row that satisfies that
* {@code WHERE} condition, and the first transaction rereads for the
* same condition, retrieving the additional "phantom" row in the second read.
* @see java.sql.Connection#TRANSACTION_SERIALIZABLE
*/
SERIALIZABLE(TransactionDefinition.ISOLATION_SERIALIZABLE);
TransactionInterceptor interceptor
Em relação a como a cadeia do interceptor é formada e executada, não entrarei em detalhes aqui, e irei me concentrar principalmente no interceptor para a anotação @Transactional.
@Override
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();
}
});
}
- Siga a função invokeWithinTransaction para salvar o código desnecessário. Pode ser visto claramente aqui que o interceptor implementa a transação da mesma maneira que implementamos manualmente a transação na camada DAO. É iniciar a transação primeiro, depois executá-la e rolar de volta se for anormal. Caso contrário, confirme a transação, mas aqui substitua a lógica de execução por uma cadeia de interceptação de execução recursiva
/**
* 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, txAttr);
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
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();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
cleanupTransactionInfo(txInfo);
}
commitTransactionAfterReturning(txInfo);
return retVal;
}
else {
final ThrowableHolder throwableHolder = new ThrowableHolder();
// 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.
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;
}
}
}