Spring源码分析：声明式事务梳理

使用注解方式简单模拟事务

样例

说明

1. 数据源采用c3p0
2. 采用JdbcTemplate持久化
3. 采用Spring事务注解

环境搭建

POM依赖

<dependency>
    <groupId>c3p0</groupId>
    <artifactId>c3p0</artifactId>
    <version>0.9.1.2</version>
</dependency>
<!-- spring提供的jdbcTemplate模块 -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-jdbc</artifactId>
    <version>4.3.12.RELEASE</version>
</dependency>
<!-- mysql链接驱动包 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.44</version>
    <scope>runtime</scope>
</dependency>
<!-- AOP -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>4.3.12.RELEASE</version>
</dependency>

配置类

/**
 * description:声明式事务配置类，其中@EnableTransactionManagement
 * 一定要开启。
 * @author 70KG
 */
@Configuration
@ComponentScan("com.nmys.story.springCore.springaop.tx_sample")
@EnableTransactionManagement // -- 开启基于注解的事务管理
public class TxConfig {

    // -- 配置数据源
    @Bean
    public DataSource dataSource() throws Exception {
        ComboPooledDataSource pool = new ComboPooledDataSource();
        pool.setUser("root");
        pool.setPassword("root");
        pool.setDriverClass("com.mysql.jdbc.Driver");
        pool.setJdbcUrl("jdbc:mysql://localhost:3306/usthe?useSSL=false");
        return pool;
    }

    // -- 加入模板
    @Bean
    public JdbcTemplate jdbcTemplate() throws Exception {
        JdbcTemplate template = new JdbcTemplate(dataSource());
        return template;
    }

    // -- 配置事务管理器，它才是用来提交回滚事务的主导者
    @Bean
    public DataSourceTransactionManager txManager() throws Exception {
        DataSourceTransactionManager tx = new DataSourceTransactionManager(dataSource());
        return tx;
    }

}

业务类

/**
 * description
 * @author 70KG
 */
@Service
public class TxService {

    @Autowired
    private TxDao txDao;

    public void insertLog(){
        txDao.insertSth();
    }

}

<!--more-->

/**
 * description
 * @author 70KG
 */
@Repository
public class TxDao {
    @Autowired
    private JdbcTemplate jdbcTemplate;

    // @Transactional仅表明它是一个事务方法，开启事务仅有注解是不够的，还需要配置事务管理器
    @Transactional
    public void insertSth() {
        String sql = "INSERT into sys_log (username) VALUES(?);";
        jdbcTemplate.update(sql, "lisi");
        System.out.println("------>插入成功");
        int i = 10/0;
    }
}

测试类

/**
 * description
 * @author 70KG
 */
public class Test01 {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(TxConfig.class);
        TxService bean = app.getBean(TxService.class);
        bean.insertLog();
    }

}

测试结果

测试结果肯定是能正常运行的，下面试着跟一下源码。

源码分析

1. 当容器开始启动运行的时候就会找到@EnableTransactionManagement注解
2. 进入注解，发现它使用@Import(TransactionManagementConfigurationSelector.class)向容器中注入了这个类
3. 跟进TransactionManagementConfigurationSelector，发现它最终实现的是ImportSelector接口，这个接口可以向IOC容器中以Bean的全类名的方式注入Bean。

源码如下，AdviceMode在注解@EnableTransactionManagement默认就是PROXY，可见它向容器中注入了两个类，分别是AutoProxyRegistrar和ProxyTransactionManagementConfiguration。

public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
    @Override
    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;
        }
    }
}

AutoProxyRegistrar

1. AutoProxyRegistrar翻译过来：自动代理注册器。进入AutoProxyRegistrar类，截取部分源码，如下：

@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    boolean candidateFound = false;
    Set<String> annoTypes = importingClassMetadata.getAnnotationTypes();
    for (String annoType : annoTypes) {
        AnnotationAttributes candidate = AnnotationConfigUtils.attributesFor(importingClassMetadata, annoType);
        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) {
                // -- 前面的代码主要是获取注解类型，注解信息等等。
                // -- 主要是这个地方，如果必要的话，就向容器中注册一个自动代理创建器。
                AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
                if ((Boolean) proxyTargetClass) {
                    AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
                    return;
                }
            }
        }
    }
    ...........

1. 进入registerAutoProxyCreatorIfNecessary(registry)，AopConfigUtils类中，源码如下：

@Nullable
private static BeanDefinition registerOrEscalateApcAsRequired(Class<?> cls, BeanDefinitionRegistry registry,
        @Nullable Object source) {
    // -- 断言
    Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    // 先判断有没有org.springframework.aop.config.internalAutoProxyCreator
    // 首次进来，肯定没有
    if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
        BeanDefinition apcDefinition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
        if (!cls.getName().equals(apcDefinition.getBeanClassName())) {
            int currentPriority = findPriorityForClass(apcDefinition.getBeanClassName());
            int requiredPriority = findPriorityForClass(cls);
            if (currentPriority < requiredPriority) {
                apcDefinition.setBeanClassName(cls.getName());
            }
        }
        return null;
    }
    // -- 将cls也就是InfrastructureAdvisorAutoProxyCreator包装成RootBeanDefinition
    RootBeanDefinition beanDefinition = new RootBeanDefinition(cls);
    beanDefinition.setSource(source);
    beanDefinition.getPropertyValues().add("order", Ordered.HIGHEST_PRECEDENCE);
    beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
    // -- 将beanDefinition注册到IOC容器中，Bean的
    // -- 名字就叫org.springframework.aop.config.internalAutoProxyCreator
    registry.registerBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME, beanDefinition);
    return beanDefinition;
}

1. 向容器中注入了InfrastructureAdvisorAutoProxyCreator，进入此类，发现父类是AbstractAdvisorAutoProxyCreator，AbstractAdvisorAutoProxyCreator的父类是AbstractAutoProxyCreator，AbstractAutoProxyCreator中的方法，创建并返回了代理类，如下：

/**
 * Create a proxy with the configured interceptors if the bean is
 * identified as one to proxy by the subclass.
 * @see #getAdvicesAndAdvisorsForBean
 */
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) throws BeansException {
    if (bean != null) {
        Object cacheKey = getCacheKey(bean.getClass(), beanName);
        if (!this.earlyProxyReferences.contains(cacheKey)) {
            return wrapIfNecessary(bean, beanName, cacheKey);
        }
    }
    return bean;
}

给容器中注入InfrastructureAdvisorAutoProxyCreator的主要作用就是，利用后置处理器机制在对象创建以后，对对象进行包装，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。

ProxyTransactionManagementConfiguration

1. 进入ProxyTransactionManagementConfiguration,部分源码如下:

// -- 向容器中注入名字为TRANSACTION_ADVISOR_BEAN_NAME的切面
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
    BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
        // -- 向切面中注入注解解析器,专门来解析事务注解的
    advisor.setTransactionAttributeSource(transactionAttributeSource());
        // -- 向切面中注入事务的拦截器,专门来拦截方法,包括事务的提交以及回滚操作
    advisor.setAdvice(transactionInterceptor());
    if (this.enableTx != null) {
        advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
    }
    return advisor;
}

1. 进入transactionAttributeSource()注解解析器,源码如下:

public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
    this.publicMethodsOnly = publicMethodsOnly;
    this.annotationParsers = new LinkedHashSet<>(2);
        // -- Spring注解的解析器
    this.annotationParsers.add(new SpringTransactionAnnotationParser());
    if (jta12Present) {
                // -- jta的解析器
        this.annotationParsers.add(new JtaTransactionAnnotationParser());
    }
    if (ejb3Present) {
                // -- ejb的解析器
        this.annotationParsers.add(new Ejb3TransactionAnnotationParser());
    }
}

1. 进入SpringTransactionAnnotationParser(),部分源码如下:

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) {

会发现@Transactional中的各种属性都在这里,这样,注解解析器就分析完了

1. 再来看事务的拦截器,分析事务是如何回滚和提交的,进入transactionInterceptor()

@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionInterceptor transactionInterceptor() {
        // -- 事务的拦截器
    TransactionInterceptor interceptor = new TransactionInterceptor();
    interceptor.setTransactionAttributeSource(transactionAttributeSource());
    if (this.txManager != null) {
                // -- 将事务管理器设置进去,为了事务的提交和回滚操作
        interceptor.setTransactionManager(this.txManager);
    }
    return interceptor;
}

TransactionInterceptor 是一个实现了MethodInterceptor接口的类,标志着TransactionInterceptor是一个方法拦截器,进入它的invoke()方法

@Override
@Nullable
public Object invoke(final 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);
}

进入invokeWithinTransaction()

@Nullable
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();
        // -- 拿到事务注解信息包括事务的qualifier和rollback信息
    final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
        // -- 获取事务管理器
    final PlatformTransactionManager tm = determineTransactionManager(txAttr);
        // -- 事务连接点的定义信息
    final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
    if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
        // 创建并开启事务
        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.
                        // -- 调用目标方法
            retVal = invocation.proceedWithInvocation();
        }
        catch (Throwable ex) {
            // target invocation exception
                        // -- 出现异常了,获取事务管理器,进行事务的回滚
            completeTransactionAfterThrowing(txInfo, ex);
            throw ex;
        }
        finally {
            cleanupTransactionInfo(txInfo);
        }
                // -- 未出现异常,也获取事务管理器则进行事务的提交
        commitTransactionAfterReturning(txInfo);
        return retVal;
    }
    .........

总结

Spring事务源码梳理

1. 通过注解@EnableTransactionManagement中的@Import(TransactionManagementConfigurationSelector.class)给容器中导入了两个组件，分别是：AutoProxyRegistrar和ProxyTransactionManagementConfiguration
2. AutoProxyRegistrar：它是一个后置处理器，给容器中注册一个InfrastructureAdvisorAutoProxyCreator，InfrastructureAdvisorAutoProxyCreator利用后置处理器机制在对象创建以后，对对象进行包装，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。
3. ProxyTransactionManagementConfiguration：给容器中注册事务增强器

• 事务增强器要用事务注解信息：AnnotationTransactionAttributeSource来解析事务注解
• 事务拦截器中：transactionInterceptor()，它是一个TransactionInterceptor(保存了事务属性信息和事务管理器)，而TransactionInterceptor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(首先获取事务相关的属性，再获取PlatformTransactionManager，如果没有指定任何transactionManager，最终会从容器中按照类型获取一个PlatformTransactionManager，最后执行目标方法，如果异常，便获取到事务管理器进行回滚，如果正常，同样拿到事务管理器提交事务。