<p> </p>
<p>平时我们都是使用注解开启事务@EnableTransactionManagement</p>
<pre class="blockcode"><code>@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(TransactionManagementConfigurationSelector.class)
public @interface EnableTransactionManagement {
//proxyTargetClass = false表示是JDK动态代理支持接口代理。true表示是Cglib代理支持子类继承代理。
boolean proxyTargetClass() default false;
//事务通知模式(切面织入方式)，默认代理模式（同一个类中方法互相调用拦截器不会生效），可以选择增强型AspectJ
AdviceMode mode() default AdviceMode.PROXY;
//连接点上有多个通知时，排序，默认最低。值越大优先级越低。
int order() default Ordered.LOWEST_PRECEDENCE;
}
</code></pre>
<p>重点看类注解@Import(TransactionManagementConfigurationSelector.class)</p>
<p> </p>
<pre class="blockcode"><code>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:
// 向Spring中添加了AutoProxyRegistrar和ProxyTransactionManagementConfiguration对应的bean
return new String[] {AutoProxyRegistrar.class.getName(),
ProxyTransactionManagementConfiguration.class.getName()};
case ASPECTJ:
// 不考虑
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);
}
}
</code></pre>
<p> </p>
<p>最终会执行selectImports方法导入需要加载的类，我们只看proxy模式下，载入了AutoProxyRegistrar、ProxyTransactionManagementConfiguration2个类。</p>
<ul><li>AutoProxyRegistrar：<code>给容器中注册一个 InfrastructureAdvisorAutoProxyCreator 组件；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；</code></li><li>ProxyTransactionManagementConfiguration：就是一个配置类，定义了事务增强器。</li></ul>
<p> </p>
<p> </p>
<p><strong>AutoProxyRegistrar</strong></p>
<p>先看AutoProxyRegistrar实现了ImportBeanDefinitionRegistrar接口，复写registerBeanDefinitions方法，源码如下：</p>
<pre class="blockcode"><code>public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
private final Log logger = LogFactory.getLog(getClass());
/**
* Register, escalate, and configure the standard auto proxy creator (APC) against the
* given registry. Works by finding the nearest annotation declared on the importing
* {@code @Configuration} class that has both {@code mode} and {@code proxyTargetClass}
* attributes. If {@code mode} is set to {@code PROXY}, the APC is registered; if
* {@code proxyTargetClass} is set to {@code true}, then the APC is forced to use
* subclass (CGLIB) proxying.
* <p>Several {@code @Enable*} annotations expose both {@code mode} and
* {@code proxyTargetClass} attributes. It is important to note that most of these
* capabilities end up sharing a {@linkplain AopConfigUtils#AUTO_PROXY_CREATOR_BEAN_NAME
* single APC}. For this reason, this implementation doesn't "care" exactly which
* annotation it finds -- as long as it exposes the right {@code mode} and
* {@code proxyTargetClass} attributes, the APC can be registered and configured all
* the same.
*/
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
boolean candidateFound = false;
Set<String> annTypes = importingClassMetadata.getAnnotationTypes();
for (String annType : annTypes) {
// 获取EnableTransactionManagement注解的属性值
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) {
// 注册一个InfrastructureAdvisorAutoProxyCreator类型的Bean
AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
if ((Boolean) proxyTargetClass) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
return;
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