Spring事务处理原理步骤详解
时间：2020-10-19 10:34:34 | 栏目：JAVA代码 | 点击：次
1、事务处理实现
实现步骤：
* 声明式事务：
*
* 环境搭建：
* 1、导入相关依赖
* 数据源、数据库驱动、Spring-jdbc模块
* 2、配置数据源、JdbcTemplate（Spring提供的简化数据库操作的工具）操作数据
* 3、给方法上标注 @Transactional 表示当前方法是一个事务方法；
* 4、 @EnableTransactionManagement 开启基于注解的事务管理功能；
* @EnableXXX
* 5、配置事务管理器来控制事务;
* @Bean
* public PlatformTransactionManager transactionManager()
代码实现：
@EnableTransactionManagement
@ComponentScan("com.atguigu.tx")
@Configuration
public class TxConfig {
//数据源
@Bean
public DataSource dataSource() throws Exception{
ComboPooledDataSource dataSource = new ComboPooledDataSource();
dataSource.setUser("root");
dataSource.setPassword("123456");
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;
}
//注册事务管理器在容器中
@Bean
public PlatformTransactionManager transactionManager() throws Exception{
return new DataSourceTransactionManager(dataSource());
}
}
2、事务处理原理
原理分析：
* 原理：
* 1）、@EnableTransactionManagement
* 利用TransactionManagementConfigurationSelector给容器中会导入组件
* 导入两个组件
* AutoProxyRegistrar
* ProxyTransactionManagementConfiguration
* 2）、AutoProxyRegistrar：
* 给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件；
* 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；
*
* 3）、ProxyTransactionManagementConfiguration 做了什么？
* 1、给容器中注册事务增强器；
* 1）、事务增强器要用事务注解的信息，AnnotationTransactionAttributeSource解析事务注解
* 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：
* 1）、先获取事务相关的属性
* 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；
* 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
*
*/
核心代码
1、EnableTransactionManagement注解，注入TransactionManagementConfigurationSelector类
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
2、TransactionManagementConfigurationSelector类，最终会导入AutoProxyRegistrar.class和ProxyTransactionManagementConfiguration.class两个组件。
public class TransactionManagementConfigurationSelector extends AdviceModeImportSelector<EnableTransactionManagement> {
/**
* Returns {@link ProxyTransactionManagementConfiguration} or
* {@code AspectJ(Jta)TransactionManagementConfiguration} for {@code PROXY}
* and {@code ASPECTJ} values of {@link EnableTransactionManagement#mode()},
* respectively.
*/
@Override
protected String[] selectImports(AdviceMode adviceMode) {
switch (adviceMode) {
case PROXY:
return new String[] {AutoProxyRegistrar.class.getName(),
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
return new String[] {determineTransactionAspectClass()};
default:
return null;
}
}
private String determineTransactionAspectClass() {
return (ClassUtils.isPresent("javax.transaction.Transactional", getClass().getClassLoader()) ?
TransactionManagementConfigUtils.JTA_TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME :
TransactionManagementConfigUtils.TRANSACTION_ASPECT_CONFIGURATION_CLASS_NAME);
}
}
3、AutoProxyRegistrar类的作用为：
给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件；
最终的目的是：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；
@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;
if (mode == AdviceMode.PROXY) {
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
}
}
}
}
if (!candidateFound && logger.isInfoEnabled()) {
String name = getClass().getSimpleName();
logger.info(String.format("%s was imported but no annotations were found " +
"having both 'mode' and 'proxyTargetClass' attributes of type " +
"AdviceMode and boolean respectively. This means that auto proxy " +
"creator registration and configuration may not have occurred as " +
"intended, and components may not be proxied as expected. Check to " +
"ensure that %s has been @Import'ed on the same class where these " +
"annotations are declared; otherwise remove the import of %s " +
"altogether.", name, name, name));
}
}
InfrastructureAdvisorAutoProxyCreator类的作用与AnnotationAwareAspectJAutoProxyCreator类的作用类似。
@SuppressWarnings("serial")
public abstract class AbstractAutoProxyCreator extends ProxyProcessorSupport
implements SmartInstantiationAwareBeanPostProcessor, BeanFactoryAware {
4、ProxyTransactionManagementConfiguration类
代理事务管理配置类
@Configuration
public class ProxyTransactionManagementConfiguration extends AbstractTransactionManagementConfiguration {
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
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();
}
@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;
}
}
TransactionInterceptor类，事务调用：invokeWithinTransaction()方法为最终执行的方法
@Override
@Nullable
public Object invoke(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);
}
TransactionAspectSupport类的最终事务方法执行：
@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();
final TransactionAttribute txAttr = (tas != null ? tas.getTransactionAttribute(method, targetClass) : null);
final PlatformTransactionManager tm = determineTransactionManager(txAttr);
final String joinpointIdentification = methodIdentification(method, targetClass, txAttr);
if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) {
// Standard transaction demarcation with getTransaction and commit/rollback calls.
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
Object retVal;
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.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
finally {
cleanupTransactionInfo(txInfo);
}
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, 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;
}
}
}