【Srping】事務的執行原理(一)
在使用事務的時候需要新增@EnableTransactionManagement註解來開啟事務,那麼就從@EnableTransactionManagement入手檢視一下事務的執行原理。
@EnableTransactionManagement
- Spring事務底層是通過AOP來完成的,而Spring AOP基於動態代理實現,可以看到mode方法預設返回了PROXY代理模式,我們只需關注代理模式下的執行流程即可
- 使用@Import匯入了TransactionManagementConfigurationSelector
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(TransactionManagementConfigurationSelector.class) public @interface EnableTransactionManagement { // 是否代理目標類 boolean proxyTargetClass() default false; // 預設使用代理模式 AdviceMode mode() default AdviceMode.PROXY; int order() default Ordered.LOWEST_PRECEDENCE; }
TransactionManagementConfigurationSelector
在selectImports方法中可以看到對模式進行了判斷:
- 如果是基於代理模式,返回AutoProxyRegistrar和ProxyTransactionManagementConfiguration類
- 如果是基於ASPECTJ,呼叫determineTransactionAspectClass方法
Spring預設使用的是代理模式,所以接下來看下AutoProxyRegistrar和ProxyTransactionManagementConfiguration裡面都有什麼。
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> { @Override protected String[] selectImports(AdviceMode adviceMode) { switch (adviceMode) { case PROXY: // 如果基於代理模式 return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()}; case ASPECTJ: // 如果基於ASPECTJ return new String[] {determineTransactionAspectClass()}; default: return null; } } private String determineTransactionAspectClass() { return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ? TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME : TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME); } }
AutoProxyRegistrar
AutoProxyRegistrar實現了ImportBeanDefinitionRegistrar介面,ImportBeanDefinitionRegistrar可以向容器中註冊Bean,跟著registerBeanDefinitions方法看下它會向容器中註冊什麼樣的bean:
public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar { @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { boolean candidateFound = false; Set<String> annTypes = importingClassMetadata.getAnnotationTypes(); for (String annType : annTypes) { AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType); if (candidate == null) { continue; } Object mode = candidate.get("mode"); Object proxyTargetClass = candidate.get("proxyTargetClass"); if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() && Boolean.class == proxyTargetClass.getClass()) { candidateFound = true; if (mode == AdviceMode.PROXY) { // 呼叫AopConfigUtils的registerAutoProxyCreatorIfNecessary向容器中註冊bean AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry); if ((Boolean) proxyTargetClass) { AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry); return; } } } } if (!candidateFound && logger.isInfoEnabled()) { String name = getClass().getSimpleName(); logger.info(String.format("%s was imported but no annotations were found " + "having both 'mode' and 'proxyTargetClass' attributes of type " + "AdviceMode and boolean respectively. This means that auto proxy " + "creator registration and configuration may not have occurred as " + "intended, and components may not be proxied as expected. Check to " + "ensure that %s has been @Import'ed on the same class where these " + "annotations are declared; otherwise remove the import of %s " + "altogether.", name, name, name)); } } }
AopConfigUtils
在AopConfigUtils中一共有三種自動代理建立器:
- InfrastructureAdvisorAutoProxyCreator
- AspectJAwareAdvisorAutoProxyCreator
- AnnotationAwareAspectJAutoProxyCreator
在registerAutoProxyCreatorIfNecessary方法中,可以看到事務使用的是InfrastructureAdvisorAutoProxyCreator型別的建立器:
public abstract class AopConfigUtils {
/**
* 自動代理建立器BeanName
*/
public static final String AUTO_PROXY_CREATOR_BEAN_NAME =
"org.springframework.aop.config.internalAutoProxyCreator";
/**
* 所有的自動代理建立器集合
*/
private static final List<Class<?>> APC_PRIORITY_LIST = new ArrayList<>(3);
static {
// 初始化
APC_PRIORITY_LIST.add(InfrastructureAdvisorAutoProxyCreator.class);
APC_PRIORITY_LIST.add(AspectJAwareAdvisorAutoProxyCreator.class); // AspectJ
APC_PRIORITY_LIST.add(AnnotationAwareAspectJAutoProxyCreator.class); // 註解
}
// AutoProxyRegistrar中呼叫的registerAutoProxyCreatorIfNecessary方法
@Nullable
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {
// 會呼叫下面那個registerAutoProxyCreatorIfNecessary方法
return registerAutoProxyCreatorIfNecessary(registry, null);
}
@Nullable
public static BeanDefinition registerAutoProxyCreatorIfNecessary(
BeanDefinitionRegistry registry, @Nullable Object source) {
// 呼叫registerOrEscalateApcAsRequired進行註冊,這裡傳入的是InfrastructureAdvisorAutoProxyCreator型別的
return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
}
@Nullable
private static BeanDefinition registerOrEscalateApcAsRequired(
Class<?> cls, BeanDefinitionRegistry registry, @Nullable Object source) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
// 判斷容器中是否已經包含代理建立器
if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
// 從容器中獲取
BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
// 判斷容器中已經存在的建立器的優先順序
int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
// 需要的建立器的優先順序
int requiredPriority = findPriorityForClass(cls);
// 如果容器中已經存在的建立器的優先順序小於需要建立的
if (currentPriority < requiredPriority) {
// 使用優先順序高的
apcDefinition.setBeanClassName(cls.getName());
}
}
return null;
}
// 建立RootBeanDefinition
RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
// 設定source
beanDefinition.setSource(source);
beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
// 註冊代理建立器
registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
return beanDefinition;
}
}
總結
AutoProxyRegistrar實現ImportBeanDefinitionRegistrar是為了向容器中註冊代理建立器,事務預設使用的是InfrastructureAdvisorAutoProxyCreator型別的。
ProxyTransactionManagementConfiguration
1. AOP概念
Advice通知:定義在切點上需要執行什麼樣的操作
PointCut切點:定義在哪些方法上使用通知
Advisor:Advice和Pointcut加起來組成了Advisor
2. 事務中的Advisor
我們已經知道事務是基於AOP實現的,在transactionAdvisor方法中可以看到建立了Advisor,然後設定了事務屬性TransactionAttributeSource和事務攔截器TransactionInterceptor:
- TransactionAttributeSource,從名字上可以看出是和事務的屬性設定相關的
- TransactionInterceptor事務攔截器相當於Advice通知
- BeanFactoryTransactionAttributeSourceAdvisor是Advisor
Advisor由Advice和PointCut組成,現在Advice已經有了,接下來看下Pointcut在哪裡。
@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor(
TransactionAttributeSource transactionAttributeSource, TransactionInterceptor transactionInterceptor) {
// 建立Advisor
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
// 設定TransactionAttributeSource,型別為AnnotationTransactionAttributeSource
advisor.setTransactionAttributeSource(transactionAttributeSource);
// 設定事務攔截器,相當於Advice
advisor.setAdvice(transactionInterceptor);
if (this.enableTx != null) {
advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
}
return advisor;
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionAttributeSource transactionAttributeSource() {
// 建立AnnotationTransactionAttributeSource
return new AnnotationTransactionAttributeSource();
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionInterceptor transactionInterceptor(TransactionAttributeSource transactionAttributeSource) {
// 建立事務攔截器
TransactionInterceptor interceptor = new TransactionInterceptor();
interceptor.setTransactionAttributeSource(transactionAttributeSource);
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}
}
BeanFactoryTransactionAttributeSourceAdvisor
BeanFactoryTransactionAttributeSourceAdvisor繼承關係如下:
除了繼承父類的屬性和方法,它自己還有兩個成員變數:
- transactionAttributeSource,實際傳入的是AnnotationTransactionAttributeSource型別的物件
-
TransactionAttributeSourcePointcut型別的切點pointcut
- 切點在例項化時實現了getTransactionAttributeSource方法,返回了transactionAttributeSource,後面的方法中需要呼叫此方法獲取transactionAttributeSource
由上面的分析可知,在建立BeanFactoryTransactionAttributeSourceAdvisor的時候,設定了TransactionInterceptor和TransactionAttributeSource,TransactionInterceptor相當於Advice,而這裡我們看到了它還有一個TransactionAttributeSourcePointcut切點:
public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {
@Nullable
private TransactionAttributeSource transactionAttributeSource; // 實際傳入的是AnnotationTransactionAttributeSource型別的
// 建立切點
private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
// 實現了getTransactionAttributeSource方法,返回的是AnnotationTransactionAttributeSource
@Override
@Nullable
protected TransactionAttributeSource getTransactionAttributeSource() {
return transactionAttributeSource;
}
};
public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
// 設定TransactionAttributeSource
this.transactionAttributeSource = transactionAttributeSource;
}
@Override
public Pointcut getPointcut() {
return this.pointcut;
}
}
TransactionAttributeSourcePointcut
TransactionAttributeSourcePointcut是一個切點,它的繼承關係如下:
Pointcut和MethodMatcher
Pointcut介面中定義了兩個方法:
- 獲取ClassFilter,ClassFilter是一個介面,裡面定義了matches方法,檢查切點是否與類匹配
- 獲取MethodMatcher,它也是一個介面,並且定義了matches方法,檢查切點是否與方法匹配
public interface Pointcut {
/**
* 返回類過濾器ClassFilter
*/
ClassFilter getClassFilter();
/**
* 返回MethodMatcher
*/
MethodMatcher getMethodMatcher();
}
public interface MethodMatcher {
/**
* 檢查方法是否匹配pointcut
*/
boolean matches(Method method, Class<?> targetClass);
/**
* 檢查方法是否匹配pointcut
*/
boolean matches(Method method, Class<?> targetClass, Object... args);
}
@FunctionalInterface
public interface ClassFilter {
/**
* 檢查類是否與pointcut匹配
*/
boolean matches(Class<?> clazz);
}
TransactionAttributeSourcePointcut是Pointcut和MethodMatcher的子類:
- 在建構函式中設定了ClassFilter,型別為TransactionAttributeSourceClassFilter,它是TransactionAttributeSourcePointcut的一個內部類,實現了ClassFilter介面中定義的matches方法,檢查pointcut與類是否匹配:
- 如果是TransactionalProxy、PlatformTransactionManager或者PersistenceExceptionTranslator的子類,則不匹配
- 獲取TransactionAttributeSource,呼叫它的isCandidateClass方法判斷是否匹配
- 實現了MethodMatcher介面中定義的matches方法,檢查pointcut是否匹配當前的方法
- 獲取TransactionAttributeSource判斷是否為空,如果不為空則呼叫getTransactionAttribute獲取事務屬性,TransactionAttributeSource為空,或者從TransactionAttributeSource獲取到的事務屬性不為空都會返回true
所以一個方法執行時開啟事務,需要滿足兩個條件,當前的方法和類都需要與事務的pointcut匹配,對應的方法分別是MethodMatcher的matches和ClassFilter的matches方法。
abstract class TransactionAttributeSourcePointcut extends StaticMethodMatcherPointcut implements Serializable {
protected TransactionAttributeSourcePointcut() {
// 設定ClassFilter
setClassFilter(new TransactionAttributeSourceClassFilter());
}
// 方法是否與切點匹配
@Override
public boolean matches(Method method, Class<?> targetClass) {
// 獲取TransactionAttributeSource,由上面的步驟可知返回的是AnnotationTransactionAttributeSource
TransactionAttributeSource tas = getTransactionAttributeSource();
// 如果TransactionAttributeSource為空,或者從TransactionAttributeSource獲取到的事務屬性不為空都會返回true
return (tas == null || tas.getTransactionAttribute(method, targetClass) != null);
}
// ClassFilter過濾器
private class TransactionAttributeSourceClassFilter implements ClassFilter {
// 切點是否與類匹配
@Override
public boolean matches(Class<?> clazz) {
// 如果TransactionalProxy、PlatformTransactionManager或者PersistenceExceptionTranslator的子類,則不匹配
if (TransactionalProxy.class.isAssignableFrom(clazz) ||
PlatformTransactionManager.class.isAssignableFrom(clazz) ||
PersistenceExceptionTranslator.class.isAssignableFrom(clazz)) {
return false;
}
// 獲取TransactionAttributeSource,由上文可知是AnnotationTransactionAttributeSource型別的
TransactionAttributeSource tas = getTransactionAttributeSource();
// 呼叫isCandidateClass方法判斷是否是匹配
return (tas == null || tas.isCandidateClass(clazz));
}
}
}
AnnotationTransactionAttributeSource
條件一:檢查類是否匹配事務切點
上面分析可知,檢查類是否與切點匹配時獲取了TransactionAttributeSource,呼叫它的isCandidateClass方法進行判斷,TransactionAttributeSource的具體實現是AnnotationTransactionAttributeSource:
- 在構造方法中,添加了註解解析器:
- Spring事務註解解析器的實現類為SpringTransactionAnnotationParser,也是預設的註解解析器。
- 如果開啟了JTA或者EJB,將會分別新增對應的解析器。
- 實現了isCandidateClass方法,實際又是呼叫註解解析器的isCandidateClass判斷是否是候選類的。
@SuppressWarnings("serial")
public class AnnotationTransactionAttributeSource extends AbstractFallbackTransactionAttributeSource
implements Serializable {
private static final boolean jta12Present;
private static final boolean ejb3Present;
static {
ClassLoader classLoader = AnnotationTransactionAttributeSource.class.getClassLoader();
jta12Present = ClassUtils.isPresent("javax.transaction.Transactional", classLoader);
ejb3Present = ClassUtils.isPresent("javax.ejb.TransactionAttribute", classLoader);
}
private final boolean publicMethodsOnly;
// 註解解析器集合
private final Set<TransactionAnnotationParser> annotationParsers;
public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
this.publicMethodsOnly = publicMethodsOnly;
// 添加註解解析器
if (jta12Present || ejb3Present) {
this.annotationParsers = new LinkedHashSet<>(4);
// 新增Spring事務註解解析器
this.annotationParsers.add(new SpringTransactionAnnotationParser());
if (jta12Present) {
// JTA事務註解解析器
this.annotationParsers.add(new JtaTransactionAnnotationParser());
}
if (ejb3Present) {
// EJB3事務註解解析器
this.annotationParsers.add(new Ejb3TransactionAnnotationParser());
}
}
else {
// 新增Spring事務註解解析器
this.annotationParsers = Collections.singleton(new SpringTransactionAnnotationParser());
}
}
// 判斷是否是候選類
@Override
public boolean isCandidateClass(Class<?> targetClass) {
for (TransactionAnnotationParser parser : this.annotationParsers) {
// 呼叫解析器的isCandidateClass方法判斷是否是候選類
if (parser.isCandidateClass(targetClass)) {
return true;
}
}
return false;
}
}
SpringTransactionAnnotationParser
-
SpringTransactionAnnotationParser實現了isCandidateClass方法,它又呼叫了AnnotationUtils的isCandidateClass判斷目標類是否是Transactional註解的候選類,AnnotationUtils中isCandidateClass的具體判斷邏輯如下:
-
如果註解類路徑以java.開頭,返回true,這裡Transactional註解不是java.開頭,它是Spring的註解類,所以這個條件不會成立
-
如果目標類的類路徑以java.開頭,或者是Ordered型別,isCandidateClass返回false,說明目標類不是某個註解的候選類
-
除去以上兩種情況之外,isCandidateClass都返回true
總結: 如果目標類的類路徑不以java.開頭(也就是說它不是java的相關類),也不是Ordered型別,說明目標類是Transactional註解的候選類。
-
-
SpringTransactionAnnotationParser實現了parseTransactionAnnotation方法,裡面包含對事物屬性的解析
public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {
@Override
public boolean isCandidateClass(Class<?> targetClass) {
// 是否是Transactional註解的候選類
return AnnotationUtils.isCandidateClass(targetClass, Transactional.class);
}
// 解析註解屬性
@Override
@Nullable
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
AnnotationAttributes attributes = AnnotatedElementUtils.findMergedAnnotationAttributes(
element, Transactional.class, false, false);
if (attributes != null) {
// 解析註解屬性
return parseTransactionAnnotation(attributes);
}
else {
return null;
}
}
/**
* 解析事務註解
*/
public TransactionAttribute parseTransactionAnnotation(Transactional ann) {
return parseTransactionAnnotation(AnnotationUtils.getAnnotationAttributes(ann, false, false));
}
/**
* 解析事務註解
*/
protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {
RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();
// 事務的傳播行為
Propagation propagation = attributes.getEnum("propagation");
rbta.setPropagationBehavior(propagation.value());
Isolation isolation = attributes.getEnum("isolation");
rbta.setIsolationLevel(isolation.value());
rbta.setTimeout(attributes.getNumber("timeout").intValue());
rbta.setReadOnly(attributes.getBoolean("readOnly"));
rbta.setQualifier(attributes.getString("value"));
List<RollbackRuleAttribute> rollbackRules = new ArrayList<>();
for (Class<?> rbRule : attributes.getClassArray("rollbackFor")) {
rollbackRules.add(new RollbackRuleAttribute(rbRule));
}
for (String rbRule : attributes.getStringArray("rollbackForClassName")) {
rollbackRules.add(new RollbackRuleAttribute(rbRule));
}
for (Class<?> rbRule : attributes.getClassArray("noRollbackFor")) {
rollbackRules.add(new NoRollbackRuleAttribute(rbRule));
}
for (String rbRule : attributes.getStringArray("noRollbackForClassName")) {
rollbackRules.add(new NoRollbackRuleAttribute(rbRule));
}
rbta.setRollbackRules(rollbackRules);
return rbta;
}
}
// AnnotationUtils
public abstract class AnnotationUtils {
/**
* 檢查目標類clazz是否是註解的候選類
*/
public static boolean isCandidateClass(Class<?> clazz, Collection<Class<? extends Annotation>> annotationTypes) {
for (Class<? extends Annotation> annotationType : annotationTypes) {
// 傳入目標類和註解,SpringTransactionAnnotationParser傳入的註解是Transactional
if (isCandidateClass(clazz, annotationType)) {
return true;
}
}
return false;
}
/**
* 檢查目標類clazz是否是註解的候選類
*/
public static boolean isCandidateClass(Class<?> clazz, Class<? extends Annotation> annotationType) {
// 傳入目標類和註解類路徑
return isCandidateClass(clazz, annotationType.getName());
}
/**
* 檢查目標類clazz是否是註解的候選類
*/
public static boolean isCandidateClass(Class<?> clazz, String annotationName) {
// 註解類路徑是否是java.開頭
if (annotationName.startsWith("java.")) {
return true;
}
// 呼叫AnnotationsScanner的hasPlainJavaAnnotationsOnly方法判斷
// hasPlainJavaAnnotationsOnly方法的判斷邏輯是:如果目標類的類路徑以java.開頭或者是Ordered類會返回true
// 所以如果目標類的類路徑以java.開頭或者是Ordered類,isCandidateClass會返回false,說明目標類不是註解的候選類
if (AnnotationsScanner.hasPlainJavaAnnotationsOnly(clazz)) {
return false;
}
// 如果註解類路徑不是java.開頭,並且目標類的類路徑不以java.開頭,也不是Ordered型別,返回true,說明目標類是某個註解的候選類
return true;
}
}
// AnnotationsScanner
abstract class AnnotationsScanner {
static boolean hasPlainJavaAnnotationsOnly(Class<?> type) {
// 如果目標類的類路徑以java.開頭或者是Ordered類
return (type.getName().startsWith("java.") || type == Ordered.class);
}
}
條件二:檢查方法是否匹配事務切點
AbstractFallbackTransactionAttributeSource
如果從TransactionAttributeSource獲取到的事務屬性不為空將會滿足切點的匹配條件,獲取事務屬性的方法實現在AbstractFallbackTransactionAttributeSource類中:
- 如果當前方法是Object中的方法,返回空
- 根據當前的方法和類的資訊構建快取key,從快取中獲取
- 如果獲取不為空,判斷是否為空的事務屬性NULL_TRANSACTION_ATTRIBUTE,如果是則返回null,否則返回從快取中獲取到的事務屬性
- 如果獲取為空,呼叫解析事務屬性的方法進行解析,然後放入快取中並返回
public abstract class AbstractFallbackTransactionAttributeSource implements TransactionAttributeSource {
// 空的TransactionAttribute
@SuppressWarnings("serial")
private static final TransactionAttribute NULL_TRANSACTION_ATTRIBUTE = new DefaultTransactionAttribute() {
@Override
public String toString() {
return "null";
}
};
// 快取
private final Map<Object, TransactionAttribute> attributeCache = new ConcurrentHashMap<>(1024);
// 獲取事務屬性
@Override
@Nullable
public TransactionAttribute getTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
// 如果當前方法所在的類是Object
if (method.getDeclaringClass() == Object.class) {
return null;
}
// 構建cacheKey
Object cacheKey = getCacheKey(method, targetClass);
// 首先根據cacheKey從快取中獲取
TransactionAttribute cached = this.attributeCache.get(cacheKey);
if (cached != null) {
// 判斷是否為空的TRANSACTION_ATTRIBUTE
if (cached == NULL_TRANSACTION_ATTRIBUTE) {
// 返回空
return null;
}
else {
// 返回事務屬性TransactionAttribute
return cached;
}
}
else {
// 解析TransactionAttribute
TransactionAttribute txAttr = computeTransactionAttribute(method, targetClass);
// 如果為空,也加入快取,但是value是NULL_TRANSACTION_ATTRIBUTE
if (txAttr == null) {
this.attributeCache.put(cacheKey, NULL_TRANSACTION_ATTRIBUTE);
}
else {
String methodIdentification = ClassUtils.getQualifiedMethodName(method, targetClass);
// 如果是DefaultTransactionAttribute型別的
if (txAttr instanceof DefaultTransactionAttribute) {
((DefaultTransactionAttribute) txAttr).setDescriptor(methodIdentification);
}
if (logger.isTraceEnabled()) {
logger.trace("Adding transactional method '" + methodIdentification + "' with attribute: " + txAttr);
}
// 加入快取
this.attributeCache.put(cacheKey, txAttr);
}
return txAttr;
}
}
// 獲取快取KEY
protected Object getCacheKey(Method method, @Nullable Class<?> targetClass) {
return new MethodClassKey(method, targetClass);
}
/**
* 解析TransactionAttribute
*/
@Nullable
protected TransactionAttribute computeTransactionAttribute(Method method, @Nullable Class<?> targetClass) {
// 判斷方法是否是public的
if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
return null;
}
// 獲取目標方法
Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);
// 在方法上查詢事務屬性的設定,findTransactionAttribute方法在AnnotationTransactionAttributeSource中實現
TransactionAttribute txAttr = findTransactionAttribute方法(specificMethod);
if (txAttr != null) {
return txAttr;
}
// 在目標類上面查詢事務屬性的設定
txAttr = findTransactionAttribute(specificMethod.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
if (specificMethod != method) {
// 使用方法上配置的事務屬性
txAttr = findTransactionAttribute(method);
if (txAttr != null) {
return txAttr;
}
// 使用類上面配置的事務屬性
txAttr = findTransactionAttribute(method.getDeclaringClass());
if (txAttr != null && ClassUtils.isUserLevelMethod(method)) {
return txAttr;
}
}
return null;
}
}
總結
事務是基於AOP實現的,事務的Advisor是BeanFactoryTransactionAttributeSourceAdvisor,Advisor判斷方法是否匹配時,是通過Pointcut的matches方法判斷的,事務的Pointcut是TransactionAttributeSourcePointcut,裡面實現了方法是否與事務切點匹配的判斷:
-
對類的匹配是通過判斷目標類是否是Transactional註解的候選類實現的,我們建立的類一般不會以java.開頭,所以說可以與Transactional註解匹配成功。
-
對方法的匹配是通過解析方法上面配置的事務屬性判斷的,如果解析到了事務屬性,則滿足匹配條件。
TransactionInterceptor
TransactionInterceptor是事務Advisor的Advice,執行目標方法時,方法會被攔截,進入到TransactionInterceptor中,在TransactionInterceptor的invoke方法中實際是呼叫invokeWithinTransaction執行的:
public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
@Override
@Nullable
public Object invoke(MethodInvocation invocation) throws Throwable {
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
// 通過事務執行目標方法,實現在TransactionAspectSupport方法中
return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);
}
}
TransactionAspectSupport
TransactionAspectSupport中實現了invokeWithinTransaction方法:
- 獲取事務屬性TransactionAttribute和TransactionManager事務管理器
- 對響應式事務、宣告式事務和程式設計式事務分別進行判斷,以宣告式事務為例步驟如下:
- 建立事務
- 執行方法
- 捕捉異常,如果丟擲異常進行回滾
- 清除事務資訊
- 提交事務
public abstract class TransactionAspectSupport implements BeanFactoryAware, InitializingBean {
@Nullable
protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,
final InvocationCallback invocation) throws Throwable {
// 獲取TransactionAttributeSource
TransactionAttributeSource tas = getTransactionAttributeSource();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
// 獲取事務管理器TransactionManager
final TransactionManager tm = determineTransactionManager(txAttr);
// 響應式事務處理
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);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
// 宣告式事務的處理
if (txAttr == null || !(ptm instanceof CallbackPreferringPlatformTransactionManager)) {
// 建立事務
TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);
Object retVal;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// 這是一個環繞通知,將會在攔截鏈中執行下一個攔截
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// 捕捉異常,進行回滾
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
// 清除事務
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);
}
}
// 提交事務
commitTransactionAfterReturning(txInfo);
return retVal;
}
// 程式設計式事務的處理
else {
final ThrowableHolder throwableHolder = new ThrowableHolder();
// It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
try {
Object result = ((CallbackPreferringPlatformTransactionManager) ptm).execute(txAttr, status -> {
// 獲取事務資訊
TransactionInfo txInfo = prepareTransactionInfo(ptm, txAttr, joinpointIdentification, status);
try {
// 執行方法
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 {
// 清除事務資訊
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;
}
}
}
}
總結
參考
Spring版本:5.2.5.RELEASE