spring注解开发-声明式事务（源码）

1. 环境搭建与测试

1）导入相关依赖

数据源、数据库驱动、Spring-jdbc模块

        <dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-jdbc</artifactId>
			<version>4.3.12.RELEASE</version>
		</dependency>
        <dependency>
			<groupId>c3p0</groupId>
			<artifactId>c3p0</artifactId>
			<version>0.9.1.2</version>
		</dependency>
        <dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>5.1.44</version>
		</dependency>

2）配置数据源、JdbcTemplate 操作数据

   //数据源
	@Bean
	public DataSource dataSource() throws Exception{
		ComboPooledDataSource dataSource = new ComboPooledDataSource();
		dataSource.setUser("root");
		dataSource.setPassword("1111");
		dataSource.setDriverClass("com.mysql.jdbc.Driver");
		dataSource.setJdbcUrl("jdbc:mysql://localhost:3306/test");
		return dataSource;
	}

	@Bean
	public JdbcTemplate jdbcTemplate() throws Exception{
		//Spring对@Configuration类会特殊处理；给容器中加组件的方法，多次调用都只是从容器中找组件
		JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource());
		return jdbcTemplate;
	}

3）给方法上标注@Transactional表示当前方法是一个事务方法；

@Transactional
	public void insertUser(){
		userDao.insert();
		//otherDao.other();
		System.out.println("插入完成...");
		int i = 10/0;
	}

4）@EnableTransactionManagement开启基于注解的事务管理功能；

5）配置事务管理器来控制事务;

    @Bean
	public PlatformTransactionManager transactionManager() throws Exception{
		return new DataSourceTransactionManager(dataSource());
	}

2. 原理分析

1）@EnableTransactionManagement利用TransactionManagementConfigurationSelector给容器中会导入组件；adviceMode默认是proxy，因此会导入两个组件AutoProxyRegistrar，ProxyTransactionManagementConfiguration

下面不是完整的类代码，只是源码中的片段整合而来，相应的类名在注释中
//EnableTransactionManagement
AdviceMode mode() default AdviceMode.PROXY;

//TransactionManagementConfigurationSelector
case PROXY:
            return new String[]{AutoProxyRegistrar.class.getName(), ProxyTransactionManagementConfiguration.class.getName()};

2）AutoProxyRegistrar：给容器中注册一个InfrastructureAdvisorAutoProxyCreator 组件；

//AopConfigUtils类
public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, Object source) {
        return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
    }

InfrastructureAdvisorAutoProxyCreator: 利用后置处理器机制在对象创建以后，包装对象，返回一个代理对象（增强器），代理对象执行方法利用拦截器链进行调用；----同AOP；

InfrastructureAdvisorAutoProxyCreator的UML图例

3)ProxyTransactionManagementConfiguration 做了什么？

1>给容器中注册事务增强器；

1.1>事务增强器要用事务注解的信息，AnnotationTransactionAttributeSource解析事务注解

    //ProxyTransactionManagementConfiguration
    @Bean
    @Role(2)
    public TransactionAttributeSource transactionAttributeSource() {
        return new AnnotationTransactionAttributeSource();
    }

    //AnnotationTransactionAttributeSource
    public AnnotationTransactionAttributeSource(TransactionAnnotationParser annotationParser) {
        this.publicMethodsOnly = true;
        Assert.notNull(annotationParser, "TransactionAnnotationParser must not be null");
        this.annotationParsers = Collections.singleton(annotationParser);
    }

1.2>事务拦截器：TransactionInterceptor；保存了事务属性信息，事务管理器；他是一个MethodInterceptor；在目标方法执行的时候；执行拦截器链；事务拦截器：

//ProxyTransactionManagementConfiguration
@Bean
    @Role(2)
    public TransactionInterceptor transactionInterceptor() {
        TransactionInterceptor interceptor = new TransactionInterceptor();
        interceptor.setTransactionAttributeSource(this.transactionAttributeSource());
        if (this.txManager != null) {
            interceptor.setTransactionManager(this.txManager);
        }
        return interceptor;
    }

1.2.1>先获取事务相关的属性

//TransactionAspectSupport
protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final TransactionAspectSupport.InvocationCallback invocation) throws Throwable {
        final TransactionAttribute txAttr = this.getTransactionAttributeSource().getTransactionAttribute(method, targetClass);

1.2.2>再获取PlatformTransactionManager,如果事先没有添加指定任何transactionmanger,最终会从容器中按照类型获取一个PlatformTransactionManager；

//TransactionAspectSupport->invokeWithinTransaction
final PlatformTransactionManager tm = this.determineTransactionManager(txAttr);
//上面的方法
protected PlatformTransactionManager determineTransactionManager(TransactionAttribute txAttr) {
        if (txAttr != null && this.beanFactory != null) {
            String qualifier = txAttr.getQualifier();
            if (StringUtils.hasText(qualifier)) {
                return this.determineQualifiedTransactionManager(qualifier);
            } else if (StringUtils.hasText(this.transactionManagerBeanName)) {
                return this.determineQualifiedTransactionManager(this.transactionManagerBeanName);
            } else {
                PlatformTransactionManager defaultTransactionManager = this.getTransactionManager();
                if (defaultTransactionManager == null) {
                    defaultTransactionManager = (PlatformTransactionManager)this.transactionManagerCache.get(DEFAULT_TRANSACTION_MANAGER_KEY);
                    if (defaultTransactionManager == null) {
                        defaultTransactionManager = (PlatformTransactionManager)this.beanFactory.getBean(PlatformTransactionManager.class);
                        this.transactionManagerCache.putIfAbsent(DEFAULT_TRANSACTION_MANAGER_KEY, defaultTransactionManager);
                    }
                }

                return defaultTransactionManager;
            }
        } else {
            return this.getTransactionManager();
        }
    }

1.2.3>执行目标方法;如果异常，获取到事务管理器，利用事务管理回滚操作；如果正常，利用事务管理器，提交事务

//TransactionAspectSupport->invokeWithinTransaction
protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final TransactionAspectSupport.InvocationCallback invocation) throws Throwable {
//获取事务属性
        final TransactionAttribute txAttr = this.getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
//事务管理器
        final PlatformTransactionManager tm = this.determineTransactionManager(txAttr);
        final String joinpointIdentification = this.methodIdentification(method, targetClass, txAttr);
        if (txAttr != null && tm instanceof CallbackPreferringPlatformTransactionManager) {
            try {
                Object result = ((CallbackPreferringPlatformTransactionManager)tm).execute(txAttr, new TransactionCallback<Object>() {
                    public Object doInTransaction(TransactionStatus status) {
                        TransactionAspectSupport.TransactionInfo txInfo = TransactionAspectSupport.this.prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);

                        TransactionAspectSupport.ThrowableHolder var4;
                        try {
                            Object var3 = invocation.proceedWithInvocation();
                            return var3;
                        } catch (Throwable var8) {
                            if (txAttr.rollbackOn(var8)) {
                                if (var8 instanceof RuntimeException) {
                                    throw (RuntimeException)var8;
                                }

                                throw new TransactionAspectSupport.ThrowableHolderException(var8);
                            }

                            var4 = new TransactionAspectSupport.ThrowableHolder(var8);
                        } finally {
                            TransactionAspectSupport.this.cleanupTransactionInfo(txInfo);
                        }

                        return var4;
                    }
                });
                if (result instanceof TransactionAspectSupport.ThrowableHolder) {
                    throw ((TransactionAspectSupport.ThrowableHolder)result).getThrowable();
                } else {
                    return result;
                }
            } catch (TransactionAspectSupport.ThrowableHolderException var14) {
                throw var14.getCause();
            }
        } else {
            TransactionAspectSupport.TransactionInfo txInfo = this.createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
            Object retVal = null;

            try {
                retVal = invocation.proceedWithInvocation();
            } catch (Throwable var15) {
        //事务异常--执行回滚操作
          this.completeTransactionAfterThrowing(txInfo, var15);
                throw var15;
            } finally {
                this.cleanupTransactionInfo(txInfo);
            }
//事务正常--执行commit
            this.commitTransactionAfterReturning(txInfo);
            return retVal;
        }
    }

commit操作:

//TransactionAspectSupport
protected void commitTransactionAfterReturning(TransactionAspectSupport.TransactionInfo txInfo) {
        if (txInfo != null && txInfo.hasTransaction()) {
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "]");
            }
            txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
        }
    }

rollback操作：

//TransactionAspectSupport
protected void completeTransactionAfterThrowing(TransactionAspectSupport.TransactionInfo txInfo, Throwable ex) {
        if (txInfo != null && txInfo.hasTransaction()) {
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "] after exception: " + ex);
            }

            if (txInfo.transactionAttribute.rollbackOn(ex)) {
                try {
                    txInfo.getTransactionManager().rollback(txInfo.getTransactionStatus());
                } catch (TransactionSystemException var7) {
                    this.logger.error("Application exception overridden by rollback exception", ex);
                    var7.initApplicationException(ex);
                    throw var7;
                } catch (RuntimeException var8) {
                    this.logger.error("Application exception overridden by rollback exception", ex);
                    throw var8;
                } catch (Error var9) {
                    this.logger.error("Application exception overridden by rollback error", ex);
                    throw var9;
                }
            } else {
                try {
                    txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
                } catch (TransactionSystemException var4) {
                    this.logger.error("Application exception overridden by commit exception", ex);
                    var4.initApplicationException(ex);
                    throw var4;
                } catch (RuntimeException var5) {
                    this.logger.error("Application exception overridden by commit exception", ex);
                    throw var5;
                } catch (Error var6) {
                    this.logger.error("Application exception overridden by commit error", ex);
                    throw var6;
                }
            }
        }

    }