• Spring笔记(5)

    一.背景

    　　前面详解了实现Spring事务的两种方式的不同实现：编程式事务和声明式事务，对于配置都使用到了xml配置，今天介绍Spring事务的注解开发，例如下面例子：

    1. 配置类：注册数据源、JDBC模板、事务管理器 
      //包扫描，将包下的dao、service注册到Spring容器中
@ComponentScan("com.hrh")
//开启基于注解的事务管理，跟@Transactional注解配套使用
@EnableTransactionManagement
//表明TxConfig是配置类
@Configuration
public class TxConfig {
    //注册数据源
    @Bean
    public DataSource dataSource() throws Exception {
        ComboPooledDataSource comboPooledDataSource = new ComboPooledDataSource();
        comboPooledDataSource.setUser("xxx");
        comboPooledDataSource.setPassword("xxx");
        comboPooledDataSource.setJdbcUrl("jdbc:mysql://xxx:3306/xxx");
        comboPooledDataSource.setDriverClass("com.mysql.jdbc.Driver");
        return comboPooledDataSource;
    }

    //注册jdbc模板
    @Bean
    public JdbcTemplate jdbcTemplate() throws Exception {
        return new JdbcTemplate(dataSource());
    }

    //注册事务管理器来控制事务
    @Bean
    public PlatformTransactionManager manager() throws Exception {
        return new DataSourceTransactionManager(dataSource());
    }
}
    2. 业务代码： 
      @Repository
public class UserDao {
    @Autowired
    private JdbcTemplate jdbcTemplate;
    public void insert(){
        String sql ="insert into tab_person(name,age) values(?,?)";
        String name = UUID.randomUUID().toString().substring(0, 5);
        jdbcTemplate.update(sql,name,19);
    }
}

@Service
public class UserService{
    @Autowired
    private UserDao userDao;
    
    //添加事务
    @Transactional
    public void insert() {
        userDao.insert();
        System.out.println("插入完成。");
        int i = 10/0;
    }
}
    3. 测试：从下面运行结果可以看出抛出了异常，在数据库中查看数据发现没有最新的数据插入，表明插入操作进行了回滚 
          public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(TxConfig.class);
        UserService bean = context.getBean(UserService.class);
        bean.insert();
        context.close();
    }
    
运行结果：
    
    插入完成。
    Exception in thread "main" java.lang.ArithmeticException: / by zero
        at com.hrh.service.UserService.insert(UserService.java:20) 

     二. @EnableTransactionManagement注解源码分析

    　　1.流程

      1. EnableTransactionManagement导入一个TransactionManagementConfigurationSelector组件

      2. TransactionManagementConfigurationSelector默认导入两个组件：AutoProxyRegistrar和ProxyTransactionManagementConfiguration

      3. AutoProxyRegistrar（利用后置处理器包装代理对象）：注册一个InfrastructureAdvisorAutoProxyCreator组件（自动代理创建器），利用后置处理器机制在对象创建之后包装对象，返回一个代理对象（增强器），利用拦截器链执行方法

      4. ProxyTransactionManagementConfiguration（注册配置）：给容器注册各种组件，注册了事务增强器

    　　　　　　　　4.1）事务增强器要用事务注解的信息，AnnotationTransactionAttributeSource解析了注解上的各种属性信息

    　　　　　　　　4.2）同时用到TransactionInterceptor事务拦截器：保存了事务属性信息、事务管理器

    　　　　　　　　　　4.2.1）在目标方法执行时：执行拦截器链（即TransactionInterceptor）

    　　　　　　　　　   4.2.2）TransactionInterceptor事务拦截器的作用：获取事务相关的属性，再获取事务管理器进行事务的执行、回滚或提交操作；

    　　2.源码解析

      1.  EnableTransactionManagement导入一个TransactionManagementConfigurationSelector组件 
        @Import({TransactionManagementConfigurationSelector.class})
public @interface EnableTransactionManagement {
    //默认为false
    boolean proxyTargetClass() default false;
    //默认为PROXY
    AdviceMode mode() default AdviceMode.PROXY;

    int order() default 2147483647;
}
      2. TransactionManagementConfigurationSelector默认导入两个组件：AutoProxyRegistrar和ProxyTransactionManagementConfiguration 
        public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
    //AdviceMode值在EnableTransactionManagement默认了
    @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;
        }
    }

}
      3. AutoProxyRegistrar（利用后置处理器包装代理对象）：注册一个InfrastructureAdvisorAutoProxyCreator组件（自动代理创建器），利用后置处理器机制在对象创建之后包装对象，返回一个代理对象（增强器），利用拦截器链执行方法 
        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;
                //注册一个InfrastructureAdvisorAutoProxyCreator组件（自动代理创建器）
                if (mode == AdviceMode.PROXY) {
                    AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
                    //proxyTargetClass在EnableTransactionManagement默认false
                    if ((Boolean) proxyTargetClass) {
                        AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
                        return;
                    }
                }
            }
        }
        .....
    }

}
        • AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry)：自动代理创建器 
          public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry) {
        return registerAutoProxyCreatorIfNecessary(registry, null);
    }

    @Nullable
    public static BeanDefinition registerAutoProxyCreatorIfNecessary(
            BeanDefinitionRegistry registry, @Nullable Object source) {
        //给容器注册InfrastructureAdvisorAutoProxyCreator（是一个后置处理器），利用后置处理器机制在对象创建之后包装对象，返回一个代理对象（增强器），利用拦截器链执行方法
        return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
    }
      4. ProxyTransactionManagementConfiguration（注册配置）：给容器注册各种组件，注册了事务增强器 
        @Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
    //注册事务增强器BeanFactoryTransactionAttributeSourceAdvisor
    @Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
        BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
        //设置事务属性,从注解解析器获取注解上的事务属性值
        advisor.setTransactionAttributeSource(transactionAttributeSource());
        //设置了TransactionInterceptor事务拦截器
        advisor.setAdvice(transactionInterceptor());
        advisor.setOrder(this.enableTx.<Integer>getNumber("order"));
        return advisor;
    }
    //注册事务属性，解析注解中的各种属性，比如propagation、isolation、timeout等
    @Bean
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public TransactionAttributeSource transactionAttributeSource() {
        //注解解析器
        return new AnnotationTransactionAttributeSource();
    }
    //注册了TransactionInterceptor事务拦截器：保存了事务属性信息、事务管理器
    @Bean
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public TransactionInterceptor transactionInterceptor() {
        TransactionInterceptor interceptor = new TransactionInterceptor();
        //保存了事务属性信息
        interceptor.setTransactionAttributeSource(transactionAttributeSource());
        if (this.txManager != null) {
            //保存了事务管理器
            interceptor.setTransactionManager(this.txManager);
        }
        return interceptor;
    }

}
        1. 注解解析器AnnotationTransactionAttributeSource 
          public AnnotationTransactionAttributeSource(boolean publicMethodsOnly) {
    this.publicMethodsOnly = publicMethodsOnly;
    this.annotationParsers = new LinkedHashSet<TransactionAnnotationParser>(4);
    //添加spring事务注解的解析器
    this.annotationParsers.add(new SpringTransactionAnnotationParser());
    if (jta12Present) {
        //添加jta事务注解的解析器
        this.annotationParsers.add(new JtaTransactionAnnotationParser());
    }
    if (ejb3Present) {
        //添加Ejb3事务注解的解析器
        this.annotationParsers.add(new Ejb3TransactionAnnotationParser());
    }
}
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement element) {
    AnnotationAttributes attributes = AnnotatedElementUtils.getMergedAnnotationAttributes(
            element, Transactional.class);
    if (attributes != null) {
        //解析注解
        return parseTransactionAnnotation(attributes);
    }
    else {
        return null;
    }
}
//解析注解Transactional上的每个属性
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"));

    List<RollbackRuleAttribute> rollbackRules = new ArrayList<RollbackRuleAttribute>();
    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;
}
        2. 事务拦截器TransactionInterceptor：是一个MethodInterceptor，方法拦截器（4个通知方法整合成了增强器，增强器整合成了MethodInterceptor。我们在容器中放置了一个代理对象，当要执行代理对象时，方法拦截器就执行了） 
          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, new InvocationCallback() {
        @Override
        public Object proceedWithInvocation() throws Throwable {
            return invocation.proceed();
        }
    });
}
protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation)
        throws Throwable {

    // If the transaction attribute is null, the method is non-transactional.
    //获取事务属性
    final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass);
    //获取事务管理器
    final PlatformTransactionManager tm = determineTransactionManager(txAttr);
    //获取执行的事务方法
    final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);

    if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
        // Standard transaction demarcation with getTransaction and commit/rollback calls.
        //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.
            //事务方法执行
            retVal = invocation.proceedWithInvocation();
        }
        catch (Throwable ex) {
            // target invocation exception
            //事务异常会获取事务管理器，利用事务管理器执行回滚操作
            completeTransactionAfterThrowing(txInfo, ex);
            throw ex;
        }
        finally {
            cleanupTransactionInfo(txInfo);
        }
        //如果正常，利用事务管理器提交事务
        commitTransactionAfterReturning(txInfo);
        return retVal;
    }

    else {
        final ThrowableHolder throwableHolder = new ThrowableHolder();

        // It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in.
        try {
            Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr,
                    new TransactionCallback<Object>() {
                        @Override
                        public Object doInTransaction(TransactionStatus status) {
                            TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);
                            try {
                                return invocation.proceedWithInvocation();
                            }
                            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 {
                                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;
        }
    }
} 
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  • 原文地址：https://www.cnblogs.com/huangrenhui/p/13849553.html
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