手写@EnableTransactionalManagement

• 定义一个注解，用于标注于方法上，标志着此方法是一个事务方法。

@Target({ElementType.METHOD,ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface MyTransaction {}

• 定义一个开启事务功能的注解

@Component
@Import(TransActionBeanPostProcessor.class)
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EnableTransactionalManagement {
}

• BeanPostProcessor Bean的后置处理器，拦截每一个创建后的对象，这里拦截的是Bean的方法上标注了MyTransaction 注解的对象，为其创建代理对象。

/**对象事务处理器*/
public class TransActionBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {//判断bean的类或者方法上是否标注了事务注解@MyTransactionMyTransaction annotation = AnnotationUtils.findAnnotation(bean.getClass(), MyTransaction.class);boolean isTxProxy = false;if (annotation == null){//从方法上寻找Method[] methods = bean.getClass().getMethods();for (Method method : methods) {annotation = AnnotationUtils.findAnnotation(method, MyTransaction.class);if (annotation != null){isTxProxy = true;break;}}}if (isTxProxy){//为Bean创建代理对象bean = TransactionProxyUtil.getTxProxyObject(bean, transactionManagement());}return bean;}//给容器中注入事务管理器@Beanpublic PlatformTransactionManagement transactionManagement(){return new PlatformTransactionManagement();}}

• JdbcTransactionStatus 定义一个事务的状态信息

public class JdbcTransactionStatus implements TransactionStatus{//private DataSource dataSource;private Connection connection;@Overridepublic void start() {//connection.setAutoCommit(false);System.out.println("connection.setAutoCommit(false); 开启事务");}@Overridepublic void commit() {//事务提交//connection.commit();System.out.println("事务提交了...");}@Overridepublic void rollback() {try {//事务回滚//connection.rollback();System.out.println("事务回滚了...");} catch (Exception throwables) {throwables.printStackTrace();}}@Overridepublic void close() {//connection.close();System.out.println("事务连接关闭了...");}
}

• PlatformTransactionManagement 定义平台事务管理器，这个事务管理器主要管理DataSource数据源，在开启事务之前将Connection和当前线程绑定。

public class PlatformTransactionManagement implements TransactionManagement{@Overridepublic TransactionStatus getTransaction() {return new JdbcTransactionStatus();}@Overridepublic void commit(TransactionStatus status) {status.commit();}@Overridepublic void rollback(TransactionStatus status) {status.rollback();}@Overridepublic void close(TransactionStatus status) {status.close();}}

/**事务管理器*/
public interface TransactionManagement {//获取一个事务TransactionStatus getTransaction();//提交事务void commit(TransactionStatus status);//回滚事务void rollback(TransactionStatus status);//关闭连接void close(TransactionStatus transaction);
}

/**事务状态定义*/
public interface TransactionStatus {void start();//提交void commit();//回滚void rollback();//关闭连接void close();
}

• 定义事务代理逻辑，创建代理对象，栏目目标方法，反射执行真正的方法，这里使用的是JDK的动态代理实现的。

public class TransactionProxyUtil {public static Object getTxProxyObject(Object source,TransactionManagement transactionManagement){Object proxyInstance = Proxy.newProxyInstance(source.getClass().getClassLoader(), source.getClass().getInterfaces(),new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {//将方法替换为实现类中的方法，否则获取不到实现类方法上标注的注解String name = method.getName();Class<?>[] parameterTypes = method.getParameterTypes();method = source.getClass().getMethod(name,parameterTypes);Object result = null;if (!method.isAnnotationPresent(MyTransaction.class)){result = method.invoke(source,args);}else {//获取切面类，封装方法//开启事务TransactionStatus transaction = transactionManagement.getTransaction();transaction.start();try {result = method.invoke(source,args);transactionManagement.commit(transaction);}catch (Throwable e){transactionManagement.rollback(transaction);}finally {transactionManagement.close(transaction);}}return result;}});return proxyInstance;}}