Spring源碼解析---事務解析

 Spring 事務源碼分析

1.分析EnableTransactionManagement

@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(TransactionManagementConfigurationSelector.class) public @interface EnableTransactionManagement {     boolean proxyTargetClass() default false;     AdviceMode mode() default AdviceMode.PROXY;     int order() default Ordered.LOWEST_PRECEDENCE; }

我們分析TransactionManagementConfigurationSelector，如下表格，是以通過ImportSelector接口的selectImports()方法傳回要注冊到容器中的的元件。

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {} public abstract class AdviceModeImportSelector<A extends Annotation> implements ImportSelector {}

那麼它注冊了哪些元件那：

protected String[] selectImports(AdviceMode adviceMode) {                    switch (adviceMode) {                             case PROXY:                                      return new String[] {AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};                             case ASPECTJ:                                      return new String[] {TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME};                             default:                                      return null;                    }          }

我們從EnableTransactionManagement的AdviceMode mode() default AdviceMode.PROXY;中看出，注冊兩個元件AutoProxyRegistrar，ProxyTransactionManagementConfiguration。

①AutoProxyRegistrar，

向容器中注冊了AutoProxyCreator即InfrastructureAdvisorAutoProxyCreator(增強自動代理建立器)這個元件。InfrastructureAdvisorAutoProxyCreator利用後置處理器機制，在對象建立以後，包裝對象，傳回代理對象。通過攔截器鍊對代理對象執行方法進行調用。

public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {     public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {    //隻給出關鍵代碼    Object proxyTargetClass = candidate.get("proxyTargetClass");                             if (mode != null && proxyTargetClass != null && AdviceMode.class == mode.getClass() &&                                                Boolean.class == proxyTargetClass.getClass()) {                                      candidateFound = true;                                      if (mode == AdviceMode.PROXY) {//預設值就是PROXY                                                AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);                                                if ((Boolean) proxyTargetClass) {//預設值是false 看EnableTransactionManagement注解                                                         AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);                                                         return;                                                }                                      }                             } } } @Nullable          public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {                    return registerAutoProxyCreatorIfNecessary(registry, null);          }          @Nullable          public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry,                             @Nullable Object source) {                    return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);          }

②ProxyTransactionManagementConfiguration

         給容器中注冊事務增強器。在注冊的時候需要事務屬性

advisor.setTransactionAttributeSource(transactionAttributeSource());

同時也加入了事務攔截器advisor.setAdvice(transactionInterceptor());

@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)          @Role(BeanDefinition.ROLE_INFRASTRUCTURE)          public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {                    BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();//事務屬性                    advisor.setTransactionAttributeSource(transactionAttributeSource());                    advisor.setAdvice(transactionInterceptor());                    if (this.enableTx != null) {                             advisor.setOrder(this.enableTx.<Integer>getNumber("order"));                    }                    return advisor;          }          @Bean          @Role(BeanDefinition.ROLE_INFRASTRUCTURE)          public TransactionAttributeSource transactionAttributeSource() {                    return new AnnotationTransactionAttributeSource();          }

注冊Spring注解解析器，jta事務注解解析器，Ejb事務注解解析器

public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {                    this.publicMethodsOnly = publicMethodsOnly;                    this.annotationParsers = new LinkedHashSet<>(2);                    this.annotationParsers.add(new SpringTransactionAnnotationParser());                    if (jta12Present) {                             this.annotationParsers.add(new JtaTransactionAnnotationParser());                    }                    if (ejb3Present) {                             this.annotationParsers.add(new Ejb3TransactionAnnotationParser());                    }          }

spring事務注解解析器，會解析我們@Transactional中定義的屬性

public class SpringTransactionAnnotationParser implements TransactionAnnotationParser, Serializable {   //隻給出關鍵代碼   protected TransactionAttribute parseTransactionAnnotation(AnnotationAttributes attributes) {                    RuleBasedTransactionAttribute rbta = new RuleBasedTransactionAttribute();                    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"));                    ArrayList<RollbackRuleAttribute> rollBackRules = new ArrayList<>();                    Class<?>[] rbf = attributes.getClassArray("rollbackFor");                    for (Class<?> rbRule : rbf) {                             RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);                             rollBackRules.add(rule);                    }                    String[] rbfc = attributes.getStringArray("rollbackForClassName");                    for (String rbRule : rbfc) {                             RollbackRuleAttribute rule = new RollbackRuleAttribute(rbRule);                             rollBackRules.add(rule);                    }                    Class<?>[] nrbf = attributes.getClassArray("noRollbackFor");                    for (Class<?> rbRule : nrbf) {                             NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);                             rollBackRules.add(rule);                    }                    String[] nrbfc = attributes.getStringArray("noRollbackForClassName");                    for (String rbRule : nrbfc) {                             NoRollbackRuleAttribute rule = new NoRollbackRuleAttribute(rbRule);                             rollBackRules.add(rule);                    }                    rbta.getRollbackRules().addAll(rollBackRules);                    return rbta;          } }

另一方面添加了事務攔截器：建立了一個TransactionInterceptor，它儲存了事務屬性資訊，事務管理器。

@Bean          @Role(BeanDefinition.ROLE_INFRASTRUCTURE)          public TransactionInterceptor transactionInterceptor() {                    TransactionInterceptor interceptor = new TransactionInterceptor();                    interceptor.setTransactionAttributeSource(transactionAttributeSource());                    if (this.txManager != null) {                             interceptor.setTransactionManager(this.txManager);                    }                    return interceptor;          }

它是一個方法攔截器，我們在容器中存放着代理對象，代理對象要執行方法法了，那麼攔截器就會攔截進行工作。

public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {      public Object invoke(final MethodInvocation invocation) throws Throwable {                                    Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);                    return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);          } }

攔截到執行的方法，首先獲得事務屬性，然後獲得事務處理器，根據事務配置判斷是否建立事務，執行目标方法，若執行過程中出現異常，那麼調用事務管理器復原，否則調用事務管理器送出事務

protected Object invokeWithinTransaction(Method method, @Nullable Class<?> targetClass,                             final InvocationCallback invocation) throws Throwable {                    //先獲得事務屬性                    TransactionAttributeSource tas = getTransactionAttributeSource();                    final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);                    //然後獲得事務管理器，預設從容器中擷取bean類型為PlatformTransactionManager的事務管理器，若制定了事務管理器，那麼就傳回制定的事務管理器                    final PlatformTransactionManager tm = determineTransactionManager(txAttr);                    final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);                    if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {                        //若有必要那麼建立事務                             TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);                             Object retVal = null;                             //先執行目标方法                             try {                                      retVal = invocation.proceedWithInvocation();                             }                             //若事務出現異常，那麼txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());事務復原                             catch (Throwable ex) {                                      completeTransactionAfterThrowing(txInfo, ex);                                      throw ex;                             }                             finally {                                      cleanupTransactionInfo(txInfo);                             }                             //若正常應用事務管理器送出事務                             commitTransactionAfterReturning(txInfo);                             return retVal;                             //省略。。。。。。                    }          }