項目中有一個功能涉及多個業務流程,且在同一個事務中,每個業務流程結束後都需要進行RPC調用,考慮到RPC調用的代價,決定做成異步調用,但是由於每個調用都必須在業務流程結束後進行,這時候就想到TransactionSynchronizationManager和TransactionSynchronizationAdapter。
TransactionSynchronizationManager這個類中由一系列的ThreadLocal ,我們需要關注的是synchronizations,在後面使用到的TransactionSynchronizationManager.isSynchronizationActive()、TransactionSynchronizationManager.registerSynchronization()和new TransactionSynchronizationAdapter(),都與它密切有關。
在Spring在開啓數據庫事務(無論是使用@Transactional註解,還是用xml配置)時,都會向其中寫入一個實例,用於自動處理Connection的獲取、提交或回滾等操作。
再看isSynchronizationActive()方法,判斷了synchronizations中是否有數據(Set<TransactionSynchronization>非null即可,並不要求其中有TransactionSynchronization實例。
再看registerSynchronization()方法,首先調用isSynchronizationActive()做一個校驗;然後將入參synchronization添加到synchronizations 中。入參synchronization中的方法不會在這裏執行,而是要等到事務執行到特定階段時纔會被調用。
TransactionSynchronizationAdapter是一個適配器:它實現了TransactionSynchronization接口,併爲每一個接口方法提供了一個空的實現。這類適配器的基本思想是:接口中定義了很多方法,然而業務代碼往往只需要實現其中一小部分。利用這種“空實現”適配器,我們可以專注於業務上需要處理的回調方法,而不用在業務類中放大量而且重複的空方法。
結合TransactionSynchronizationManager和TransactionSynchronizationAdapter利用ThreadPoolExecutor實現一個事務後多線程處理功能。
package com.*.module.spring.support; import com.google.common.util.concurrent.ThreadFactoryBuilder; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.transaction.support.TransactionSynchronizationAdapter; import org.springframework.transaction.support.TransactionSynchronizationManager; import java.util.ArrayList; import java.util.List; import java.util.concurrent.*; /** * 事務提交異步線程 * * @author ly */ public class TransactionAfterCommitExecutor extends ThreadPoolExecutor { private static final Logger LOGGER = LoggerFactory.getLogger(TransactionAfterCommitExecutor.class); public TransactionAfterCommitExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue); } public TransactionAfterCommitExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory); } public TransactionAfterCommitExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler); } public TransactionAfterCommitExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler); } private ThreadLocal<List<Runnable>> currentRunables = new ThreadLocal<List<Runnable>>(){ @Override protected List<Runnable> initialValue() { return new ArrayList<>(5); } }; private ThreadLocal<Boolean> registed = new ThreadLocal<Boolean>(){ @Override protected Boolean initialValue() { return false; } }; /** * 默認策略丟棄最老的數據 */ public TransactionAfterCommitExecutor() { this( 50, 500, 500L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(1024), new ThreadFactoryBuilder().setNameFormat("transaction-after-commit-call-pool-%d").build(), new ThreadPoolExecutor.DiscardOldestPolicy()); } @Override public void execute(final Runnable runnable) { //如果事務同步未啓用則認爲事務已經提交,馬上進行異步處理 if (!TransactionSynchronizationManager.isSynchronizationActive()) { super.execute(runnable); } else { //同一個事務的合併到一起處理 currentRunables.get().add(runnable); //如果存在事務則在事務結束後異步處理 if(!registed.get()){ TransactionSynchronizationManager.registerSynchronization(new AfterCommitTransactionSynchronizationAdapter()); registed.set(true); } } } @Override public Future<?> submit(final Runnable runnable) { //如果事務同步未啓用則認爲事務已經提交,馬上進行異步處理 if (!TransactionSynchronizationManager.isSynchronizationActive()) { return super.submit(runnable); } else { final RunnableFuture<Void> ftask = newTaskFor(runnable, null); //如果存在事務則在事務結束後異步處理 TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() { @Override public void afterCommit() { TransactionAfterCommitExecutor.super.submit(ftask); } }); return ftask; } } private class AfterCommitTransactionSynchronizationAdapter extends TransactionSynchronizationAdapter{ @Override public void afterCompletion(int status) { final List<Runnable> txRunables = new ArrayList<>(currentRunables.get()); currentRunables.remove(); registed.remove(); if(status == STATUS_COMMITTED){ TransactionAfterCommitExecutor.super.execute(new Runnable() { @Override public void run() { for (Runnable runnable : txRunables) { try { runnable.run(); } catch (Exception e) { LOGGER.error("ex:",e); } } } }); } } } }