Spring 源代码阅读之声明式事务

事务控制流程

例如对如下代码进行事务控制

class service1{
    method1(){
        method2();
    }
}
class service2{
    method2();
}

原理：建立一个method interceptor 拦截service的方法，在方法开始前begin事务，方法结束后commit事务

对于上述例子的流程为：

1）method1 begin transaction，新建一个事务并将该事务存储到当前线程当中，建立一个对象transInfo，存储方法id和transaction引用，并标记status为new

2）method1 proceed（出现异常回滚事务）

3）method2 begin transaction，判断当前线程是否有事务，如果有则使用当前事务，建立一个对象transInfo，标记status为exist

4）method2 proceed（出现异常回滚事务）

5）method2 commit 判断transInfo 状态是否为new，否则跳过提交

6）method1 commit 因为状态是new，所以提交

1.  初始化事务配置信息TransactionProxyFactoryBean

package org.springframework.transaction.interceptor;

import java.util.Properties;

import org.springframework.aop.Pointcut;
import org.springframework.aop.framework.AbstractSingletonProxyFactoryBean;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.transaction.PlatformTransactionManager;

public class TransactionProxyFactoryBean extends AbstractSingletonProxyFactoryBean
        implements BeanFactoryAware {

    private final TransactionInterceptor transactionInterceptor = new TransactionInterceptor();

    private Pointcut pointcut;

    public void setTransactionManager(PlatformTransactionManager transactionManager) {
        this.transactionInterceptor.setTransactionManager(transactionManager);
    }

    public void setTransactionAttributes(Properties transactionAttributes) {
        this.transactionInterceptor.setTransactionAttributes(transactionAttributes);
    }

    public void setTransactionAttributeSource(TransactionAttributeSource transactionAttributeSource) {
        this.transactionInterceptor.setTransactionAttributeSource(transactionAttributeSource);
    }

    public void setPointcut(Pointcut pointcut) {
        this.pointcut = pointcut;
    }

    public void setBeanFactory(BeanFactory beanFactory) {
        this.transactionInterceptor.setBeanFactory(beanFactory);
    }

    @Override
    protected Object createMainInterceptor() {
        this.transactionInterceptor.afterPropertiesSet();
        if (this.pointcut != null) {
            return new DefaultPointcutAdvisor(this.pointcut, this.transactionInterceptor);
        }
        else {
            // Rely on default pointcut.
            return new TransactionAttributeSourceAdvisor(this.transactionInterceptor);
        }
    }

}

2.TransactionInterceptor 事务拦截器

package org.springframework.transaction.interceptor;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Properties;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.support.AopUtils;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.TransactionStatus;
import org.springframework.transaction.support.CallbackPreferringPlatformTransactionManager;
import org.springframework.transaction.support.TransactionCallback;

@SuppressWarnings("serial")
public class TransactionInterceptor extends TransactionAspectSupport implements MethodInterceptor, Serializable {
           //拦截methods进行事务处理，每个advisor都会进行一次拦截
     public Object invoke(final MethodInvocation invocation) throws Throwable {
        // Work out the target class: may be <code>null</code>.
        // 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);

        // If the transaction attribute is null, the method is non-transactional.
        final TransactionAttribute txAttr =
                getTransactionAttributeSource().getTransactionAttribute(invocation.getMethod(), targetClass);
        //获取TransactionManager,一般情况下为配置文件配置好的TranstionManager
                final PlatformTransactionManager tm = determineTransactionManager(txAttr);
        final String joinpointIdentification = methodIdentification(invocation.getMethod(), targetClass);

        if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
            // Standard transaction demarcation with getTransaction and commit/rollback calls.
            //开始一个事务，将事务信息封装到TransactionInfo 并绑定到当前线程
                        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.proceed();
            }
            catch (Throwable ex) {
                // target invocation exception
                         //出现异常时对事务做相应处理
                completeTransactionAfterThrowing(txInfo, ex);
                throw ex;
            }
            finally {
                cleanupTransactionInfo(txInfo);
            }
                       //提交事务
            commitTransactionAfterReturning(txInfo);
            return retVal;
        }

        else {
            // It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
            try {
                Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr,
                        new TransactionCallback<Object>() {
                            public Object doInTransaction(TransactionStatus status) {
                                TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
                                try {
                                    return invocation.proceed();
                                }
                                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.
                                        return new ThrowableHolder(ex);
                                    }
                                }
                                finally {
                                    cleanupTransactionInfo(txInfo);
                                }
                            }
                        });

                // Check result: It might indicate a Throwable to rethrow.
                if (result instanceof ThrowableHolder) {
                    throw ((ThrowableHolder) result).getThrowable();
                }
                else {
                    return result;
                }
            }
            catch (ThrowableHolderException ex) {
                throw ex.getCause();
            }
        }
    }

}

2.1事务开启相关源代码研究

TransactionInterceptor invoke方法中

//开始一个事务，并将事务信息封装到TransactionInfo
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);

跟进该方法源代码：

Class TransactionAspectSupport

protected TransactionInfo createTransactionIfNecessary(
            PlatformTransactionManager tm, TransactionAttribute txAttr, final String joinpointIdentification) {

        // If no name specified, apply method identification as transaction name.
        if (txAttr != null && txAttr.getName() == null) {
            txAttr = new DelegatingTransactionAttribute(txAttr) {
                @Override
                public String getName() {
                    return joinpointIdentification;
                }
            };
        }

        TransactionStatus status = null;
        if (txAttr != null) {
            if (tm != null) {
                                //如果当前线程中没有事务，则开启一个事务，若事务已经存在，则使用该事务
                status = tm.getTransaction(txAttr);
            }
            else {
                if (logger.isDebugEnabled()) {
                    logger.debug("Skipping transactional joinpoint [" + joinpointIdentification +
                            "] because no transaction manager has been configured");
                }
            }
        }
        return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
    }

createTransactionIfNecessary方法中

//如果当前线程中没有事务，则开启一个事务，若事务已经存在，则使用该事务
status = tm.getTransaction(txAttr);

跟进该方法源代码：

ClassAbstractPlatformTransactionManager

public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
        Object transaction = doGetTransaction();//调用具体的TransactionManager实现类获取Transaction

        // Cache debug flag to avoid repeated checks.
        boolean debugEnabled = logger.isDebugEnabled();

        if (definition == null) {
            // Use defaults if no transaction definition given.
            definition = new DefaultTransactionDefinition();
        }

        if (isExistingTransaction(transaction)) {
            // Existing transaction found -> check propagation behavior to find out how to behave.
            return handleExistingTransaction(definition, transaction, debugEnabled);
        }

        // Check definition settings for new transaction.
        if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
            throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
        }

        // No existing transaction found -> check propagation behavior to find out how to proceed.
        if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
            throw new IllegalTransactionStateException(
                    "No existing transaction found for transaction marked with propagation 'mandatory'");
        }
        else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
                definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
            definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
            SuspendedResourcesHolder suspendedResources = suspend(null);
            if (debugEnabled) {
                logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
            }
            try {
                boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
                DefaultTransactionStatus status = newTransactionStatus(
                        definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
                //调用具体TransactionManager开启事务的方法
                                doBegin(transaction, definition);
                prepareSynchronization(status, definition);
                return status;
            }
            catch (RuntimeException ex) {
                resume(null, suspendedResources);
                throw ex;
            }
            catch (Error err) {
                resume(null, suspendedResources);
                throw err;
            }
        }
        else {
            // Create "empty" transaction: no actual transaction, but potentially synchronization.
            boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
            return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
        }
    }

getTransaction方法中

//调用具体TransactionManager开启事务的方法
 doBegin(transaction, definition);

跟进其源代码：

ClassHibernateTransactionManager

@Override
    protected void doBegin(Object transaction, TransactionDefinition definition) {
        HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;

        if (txObject.hasConnectionHolder() && !txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
            throw new IllegalTransactionStateException(
                    "Pre-bound JDBC Connection found! HibernateTransactionManager does not support " +
                    "running within DataSourceTransactionManager if told to manage the DataSource itself. " +
                    "It is recommended to use a single HibernateTransactionManager for all transactions " +
                    "on a single DataSource, no matter whether Hibernate or JDBC access.");
        }

        Session session = null;

        try {
            if (txObject.getSessionHolder() == null || txObject.getSessionHolder().isSynchronizedWithTransaction()) {
                Interceptor entityInterceptor = getEntityInterceptor();
                Session newSession = (entityInterceptor != null ?
                        getSessionFactory().openSession(entityInterceptor) : getSessionFactory().openSession());
                if (logger.isDebugEnabled()) {
                    logger.debug("Opened new Session [" + SessionFactoryUtils.toString(newSession) +
                            "] for Hibernate transaction");
                }
                txObject.setSession(newSession);
            }

            session = txObject.getSessionHolder().getSession();

            if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
                // We're allowed to change the transaction settings of the JDBC Connection.
                if (logger.isDebugEnabled()) {
                    logger.debug(
                            "Preparing JDBC Connection of Hibernate Session [" + SessionFactoryUtils.toString(session) + "]");
                }
                Connection con = session.connection();
                Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
                txObject.setPreviousIsolationLevel(previousIsolationLevel);
            }
            else {
                // Not allowed to change the transaction settings of the JDBC Connection.
                if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
                    // We should set a specific isolation level but are not allowed to...
                    throw new InvalidIsolationLevelException(
                            "HibernateTransactionManager is not allowed to support custom isolation levels: " +
                            "make sure that its 'prepareConnection' flag is on (the default) and that the " +
                            "Hibernate connection release mode is set to 'on_close' (SpringTransactionFactory's default). " +
                            "Make sure that your LocalSessionFactoryBean actually uses SpringTransactionFactory: Your " +
                            "Hibernate properties should *not* include a 'hibernate.transaction.factory_class' property!");
                }
                if (logger.isDebugEnabled()) {
                    logger.debug(
                            "Not preparing JDBC Connection of Hibernate Session [" + SessionFactoryUtils.toString(session) + "]");
                }
            }

            if (definition.isReadOnly() && txObject.isNewSession()) {
                // Just set to NEVER in case of a new Session for this transaction.
                session.setFlushMode(FlushMode.MANUAL);
            }

            if (!definition.isReadOnly() && !txObject.isNewSession()) {
                // We need AUTO or COMMIT for a non-read-only transaction.
                FlushMode flushMode = session.getFlushMode();
                if (flushMode.lessThan(FlushMode.COMMIT)) {
                    session.setFlushMode(FlushMode.AUTO);
                    txObject.getSessionHolder().setPreviousFlushMode(flushMode);
                }
            }

            Transaction hibTx;

            // Register transaction timeout.
            int timeout = determineTimeout(definition);
            if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                // Use Hibernate's own transaction timeout mechanism on Hibernate 3.1+
                // Applies to all statements, also to inserts, updates and deletes!
                hibTx = session.getTransaction();
                hibTx.setTimeout(timeout);
                hibTx.begin();
            }
            else {
                // Open a plain Hibernate transaction without specified timeout.
                hibTx = session.beginTransaction();
            }

            // Add the Hibernate transaction to the session holder.
            txObject.getSessionHolder().setTransaction(hibTx);

            // Register the Hibernate Session's JDBC Connection for the DataSource, if set.
            if (getDataSource() != null) {
                Connection con = session.connection();
                ConnectionHolder conHolder = new ConnectionHolder(con);
                if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                    conHolder.setTimeoutInSeconds(timeout);
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Exposing Hibernate transaction as JDBC transaction [" + con + "]");
                }
                TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
                txObject.setConnectionHolder(conHolder);
            }

            // Bind the session holder to the thread.
            if (txObject.isNewSessionHolder()) {
                TransactionSynchronizationManager.bindResource(getSessionFactory(), txObject.getSessionHolder());
            }
            txObject.getSessionHolder().setSynchronizedWithTransaction(true);
        }

        catch (Exception ex) {
            if (txObject.isNewSession()) {
                try {
                    if (session.getTransaction().isActive()) {
                        session.getTransaction().rollback();
                    }
                }
                catch (Throwable ex2) {
                    logger.debug("Could not rollback Session after failed transaction begin", ex);
                }
                finally {
                    SessionFactoryUtils.closeSession(session);
                }
            }
            throw new CannotCreateTransactionException("Could not open Hibernate Session for transaction", ex);
        }
    }