Seata源码（八）Seata事务生命周期hook

Java极客 | 作者 / 铿然一叶 这是Java极客的第 99 篇原创文章

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1. hook概述

Seata提供给了事务处理hook，在事务的生命周期过程中可以扩展处理逻辑。事务hook，可由开发者定制实现，相关类结构如下:

类	描述
TransactionalTemplate	事务模版，在事务生命周期各个环节调用hook方法
TransactionHookManager	事务hook管理类，注册和获取hook
TransactionHook	事务生命周期hook接口
TransactionHookAdapter	事务生命周期hook默认实现，什么也没做，都是空方法

TransactionHook接口的方法都没有传入参数，只能通过线程变量获取相关数据，例如： RootContext.getXID()

此接口可能在实际使用中还有扩展空间，应允许传入一些需要的参数，否则能做的事情有限。

2. hook注册和获取

2.1 注册

直接调用TransactionHookManager的静态方法registerHook完成注册

        // 线程变量, scope为当前线程
        private static final ThreadLocal<List<TransactionHook>> LOCAL_HOOKS = new ThreadLocal<>();

        public static void registerHook(TransactionHook transactionHook) {
            if (transactionHook == null) {
                throw new NullPointerException("transactionHook must not be null");
            }
            List<TransactionHook> transactionHooks = LOCAL_HOOKS.get();
            if (transactionHooks == null) {
                LOCAL_HOOKS.set(new ArrayList<>());
            }
            LOCAL_HOOKS.get().add(transactionHook);
        }

2.2 获取

TransactionHookManager.java

    public static List<TransactionHook> getHooks() throws IllegalStateException {
        List<TransactionHook> hooks = LOCAL_HOOKS.get();

        if (hooks == null || hooks.isEmpty()) {
            return Collections.emptyList();
        }
        return Collections.unmodifiableList(hooks);
    }

3. hook调用点

3.1 beforeBegin和beforeBegin

TransactionalTemplate.java

    private void beginTransaction(TransactionInfo txInfo, GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
        try {
            // TransactionHook.beforeBegin();
            triggerBeforeBegin();
            tx.begin(txInfo.getTimeOut(), txInfo.getName());
            // TransactionHook.afterBegin();
            triggerAfterBegin();
        } catch (TransactionException txe) {
            throw new TransactionalExecutor.ExecutionException(tx, txe,
                TransactionalExecutor.Code.BeginFailure);

        }
    }

    private void triggerBeforeBegin() {
        for (TransactionHook hook : getCurrentHooks()) {
            try {
                hook.beforeBegin();
            } catch (Exception e) {
                LOGGER.error("Failed execute beforeBegin in hook {}", e.getMessage(), e);
            }
        }
    }

    private void triggerAfterBegin() {
        for (TransactionHook hook : getCurrentHooks()) {
            try {
                hook.afterBegin();
            } catch (Exception e) {
                LOGGER.error("Failed execute afterBegin in hook {}", e.getMessage(), e);
            }
        }
    }

3.2 beforeCommit和afterCommit

TransactionalTemplate.java

    private void commitTransaction(GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
        try {
            triggerBeforeCommit();
            tx.commit();
            triggerAfterCommit();
        } catch (TransactionException txe) {
            // 4.1 Failed to commit
            throw new TransactionalExecutor.ExecutionException(tx, txe,
                TransactionalExecutor.Code.CommitFailure);
        }
    }

triggerBeforeCommi和triggerAfterCommit方法调用逻辑同前。

3.3 beforeRollback和afterRollback

TransactionalTemplate.java

    private void rollbackTransaction(GlobalTransaction tx, Throwable originalException) throws TransactionException, TransactionalExecutor.ExecutionException {
        triggerBeforeRollback();
        tx.rollback();
        triggerAfterRollback();
        // 3.1 Successfully rolled back
        throw new TransactionalExecutor.ExecutionException(tx, GlobalStatus.RollbackRetrying.equals(tx.getLocalStatus())
            ? TransactionalExecutor.Code.RollbackRetrying : TransactionalExecutor.Code.RollbackDone, originalException);
    }

triggerBeforeRollback和triggerAfterRollback方法调用逻辑同前。

3.4 afterCompletion

TransactionalTemplate.java 在所有操作执行完成后finally块中执行。

    public Object execute(TransactionalExecutor business) throws Throwable {
            // 此处省略XXXX行
            } finally {
                //5. clear
                resumeGlobalLockConfig(previousConfig);
                triggerAfterCompletion();
                cleanUp();
            }

end.

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