1、spring事務的簡單概述
由於實現事務功能的方式各不相同，Spring進行了統一的抽象，形成了PlatformTransactionManager事務管理器頂級介面（平臺事務管理器），事務的提交、回滾等操作全部交給它來實現
先來看下三大介面
PlatformTransactionManager： 事務管理器TransactionDefinition： 事務的一些基礎資訊，如超時時間、隔離級別、傳播屬性等TransactionStatus： 事務的一些狀態資訊，如是否是一個新的事務、是否已被標記為回滾
2、PlatformTransactionManager
相關類方法：
public interface PlatformTransactionManager {
//獲取事務狀態
TransactionStatus getTransaction(@Nullable TransactionDefinition definition) throws TransactionException;
//事務提交
void commit(TransactionStatus status) throws TransactionException;
//事務回滾
void rollback(TransactionStatus status) throws TransactionException;
}複製程式碼繼承關係：
PlatformTransactionManager
AbstractPlatformTransactionManager
DataSourceTransactionManager（重點）
HibernateTransactionManager
JpaTransactionManager複製程式碼觸發不同的事物管理器
springboot對PlatformTransactionManager的預設配置實現（引用spring-boot-starter-web中jdbc相關jar）
public class DataSourceTransactionManagerAutoConfiguration {
@Configuration
@ConditionalOnSingleCandidate(DataSource.class)
static class DataSourceTransactionManagerConfiguration {
private final DataSource dataSource;
private final TransactionManagerCustomizers transactionManagerCustomizers;
DataSourceTransactionManagerConfiguration(DataSource dataSource,
ObjectProvider<TransactionManagerCustomizers> transactionManagerCustomizers) {
this.dataSource = dataSource;
this.transactionManagerCustomizers = transactionManagerCustomizers
.getIfAvailable();
}
@Bean
@ConditionalOnMissingBean(PlatformTransactionManager.class)
public DataSourceTransactionManager transactionManager(
DataSourceProperties properties) {
DataSourceTransactionManager transactionManager = new DataSourceTransactionManager(
this.dataSource);
if (this.transactionManagerCustomizers != null) {
this.transactionManagerCustomizers.customize(transactionManager);
}
return transactionManager;
}
}
}複製程式碼通過@ConditionalOnMissingBean(PlatformTransactionManager.class)這個註解可以直到如果沒有手動配置
PlatformTransactionManager即使用預設的子類DataSourceTransactionManager來管理實務
3、事務傳播特性和隔離級別
public interface TransactionDefinition {
事務傳播特性：
1、支援事務，如果當前執行緒沒有事務，新建一個事務
int PROPAGATION_REQUIRED = 0;
2、支援事務，如果當前執行緒沒有事務，則以非事務執行
int PROPAGATION_SUPPORTS = 1;
3、 當前如果有事務，Spring就會使用該事務；否則會丟擲異常
int PROPAGATION_MANDATORY = 2;
4、如果當前執行緒存在事務，或者不存在事務，都會新建一個事務，並且新建事務與當前事務是相互隔離的，如果新建事務執行時，會先將當前事務掛起，等新建事務執行完成後，再將放行當前事務，如果新事物出現異常，會正常回滾，但不會影響當前事務
int PROPAGATION_REQUIRES_NEW = 3;
5、 不支援事務，如果存在事務，則會將當前事務掛起，以非事務執行
int PROPAGATION_NOT_SUPPORTED = 4;
6、不支援事務，如果當前執行緒存在事務，將會拋異常
int PROPAGATION_NEVER = 5;
7、如果當前執行緒存在事務，則新建一個回滾點，如果出現異常，則會回滾到上一個回滾點，對於當前事務是不受任何影響的。
int PROPAGATION_NESTED = 6;
//隔離級別：預設的隔離級別（對mysql資料庫來說就是ISOLATION_ READ_COMMITTED，可以重複讀）
int ISOLATION_DEFAULT = -1;
//隔離級別：讀未提交
int ISOLATION_READ_UNCOMMITTED = Connection.TRANSACTION_READ_UNCOMMITTED;
//隔離級別：讀已提交
int ISOLATION_READ_COMMITTED = Connection.TRANSACTION_READ_COMMITTED;
//隔離級別：可重複讀
int ISOLATION_REPEATABLE_READ = Connection.TRANSACTION_REPEATABLE_READ;
//隔離級別：序列化
int ISOLATION_SERIALIZABLE = Connection.TRANSACTION_SERIALIZABLE;
int TIMEOUT_DEFAULT = -1;
int getPropagationBehavior();
int getIsolationLevel();
int getTimeout();
boolean isReadOnly();
@Nullable
String getName();
}
複製程式碼4、為什麼說spring事務是aop的一種實現
finishBeanFactoryInitialization(beanFactory);一路向後debug最後可以看到下面的程式碼
複製程式碼protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
//這裡就是獲取需要代理的類（如果存在advice）複製程式碼//獲取bean對應的advice集合。
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
//將獲取到的advice集合儲存到代理物件中並返回。
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}複製程式碼這裡是建立代理的方法
protected Object createProxy(Class<?> beanClass, @Nullable String beanName,
@Nullable Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
//將advice封裝到 advisors中
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
proxyFactory.addAdvisors(advisors);
//這裡的targetSource就是目標物件，在後面呼叫的時候會用到
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
return proxyFactory.getProxy(getProxyClassLoader());
}
specificInterceptors是攔截器（如果是aop則是前置後置這些過濾器，如果是事務，則是事務攔截器）
BeanFactoryCacheOperationSourceAdvisor（儲存了增強的資訊）切面記錄是前置，後置等增強攔截器鏈而事務相關記錄的是事務攔截器private final Map<Object, TransactionAttribute> attributeCache = new ConcurrentHashMap<>(1024);儲存方法對應的事務資訊private final Map<Object, Boolean> advisedBeans = new ConcurrentHashMap<>(256);儲存這個bean是否為增強beanif (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) { return bean;}判斷這個bean是否為代理類，如果不是直接返回單例和多例的區別：
protected void addSingleton(String beanName, Object singletonObject) { synchronized (this.singletonObjects) { this.singletonObjects.put(beanName, singletonObject); this.singletonFactories.remove(beanName); this.earlySingletonObjects.remove(beanName); this.registeredSingletons.add(beanName); }}將獲取到的bean儲存到singletonObjects中private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);在每次呼叫的時候，直接從singletonObjects這個ConcurrentHashMap中獲取即可。如果是Prototype在從走一遍單例的流程else if (mbd.isPrototype()) { // It's a prototype -> create a new instance. Object prototypeInstance = null; try { beforePrototypeCreation(beanName); prototypeInstance = createBean(beanName, mbd, args); } finally { afterPrototypeCreation(beanName); } bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);}複製程式碼5、事務方法呼叫
和aop呼叫一樣，最後會呼叫TransactionInterceptor的invock方法
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);
}複製程式碼然後會呼叫父類TransactionAspectSupport的invokeWithinTransaction方法
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();
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)) {
// 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, 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;
}
}
}複製程式碼