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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萌新快速成长之路
JAVA编程思想（一）通过依赖注入增加扩展性
JAVA编程思想（二）如何面向接口编程
JAVA编程思想（三）去掉别扭的if，自注册策略模式优雅满足开闭原则
JAVA编程思想（四）Builder模式经典范式以及和工厂模式如何选？
Java编程思想（七）使用组合和继承的场景
JAVA基础（一）简单、透彻理解内部类和静态内部类
JAVA基础（二）内存优化-使用Java引用做缓存
JAVA基础（三）ClassLoader实现热加载
JAVA基础（四）枚举（enum）和常量定义，工厂类使用对比
JAVA基础（五）函数式接口-复用，解耦之利刃\
如何编写软件设计文档
Seata源码（一）初始化
Seata源码（二）事务基础对象
Seata源码（三）事务处理类结构和流程
Seata源码（四）全局锁GlobalLock
Seata源码（五）Seata数据库操作
Seata源码（六）Seata的undo日志操作
Seata源码（七）Seata事务故障处理\
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
java
// 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
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
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
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
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。
java
public Object execute(TransactionalExecutor business) throws Throwable {
// 此处省略XXXX行
} finally {
//5. clear
resumeGlobalLockConfig(previousConfig);
triggerAfterCompletion();
cleanUp();
}end.
