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一、引言
海内商城从印度做起，缓缓的会有一些其余国家的诉求，这个时候须要咱们针对以后的商城做一个革新，能够撑持多个国家的商城，这里会波及多个问题，多语言，多国家，多时区，本地化等等。在多国家的状况下如何把辨认进去的国家信息传递上来，一层一层直到代码执行的最初一步。甚至还有一些多线程的场景须要解决。
二、背景技术
2.1 ThreadLocal
ThreadLocal 是最容易想到了，入口辨认到国家信息后，丢进 ThreadLocal，这样后续代码、redis、DB 等做国家辨别的时候都能应用到。
这里先简略介绍一下 ThreadLocal：
/**
* Sets the current thread's copy of this thread-local variable
* to the specified value. Most subclasses will have no need to
* override this method, relying solely on the {@link #initialValue}
* method to set the values of thread-locals.
*
* @param value the value to be stored in the current thread's copy of
* this thread-local.
*/
public void set(T value) {Thread t = Thread.currentThread();
ThreadLocalMap map = getMap(t);
if (map != null)
map.set(this, value);
else
createMap(t, value);
}
/**
* Returns the value in the current thread's copy of this
* thread-local variable. If the variable has no value for the
* current thread, it is first initialized to the value returned
* by an invocation of the {@link #initialValue} method.
*
* @return the current thread's value of this thread-local
*/
public T get() {Thread t = Thread.currentThread();
ThreadLocalMap map = getMap(t);
if (map != null) {ThreadLocalMap.Entry e = map.getEntry(this);
if (e != null) {@SuppressWarnings("unchecked")
T result = (T)e.value;
return result;
}
}
return setInitialValue();}
/**
* Get the map associated with a ThreadLocal. Overridden in
* InheritableThreadLocal.
*
* @param t the current thread
* @return the map
*/
ThreadLocalMap getMap(Thread t) {return t.threadLocals;}
/**
* Get the entry associated with key. This method
* itself handles only the fast path: a direct hit of existing
* key. It otherwise relays to getEntryAfterMiss. This is
* designed to maximize performance for direct hits, in part
* by making this method readily inlinable.
*
* @param key the thread local object
* @return the entry associated with key, or null if no such
*/
private Entry getEntry(ThreadLocal<?> key) {int i = key.threadLocalHashCode & (table.length - 1);
Entry e = table[i];
if (e != null && e.get() == key)
return e;
else
return getEntryAfterMiss(key, i, e);
}- 每一个 Thread 线程都有属于本人的 threadLocals(ThreadLocalMap), 外面有一个弱援用的 Entry(ThreadLocal,Object)。
- get 办法首先通过 Thread.currentThread 失去以后线程，而后拿到线程的 threadLocals(ThreadLocalMap)，再从 Entry 中获得以后线程存储的 value。
- set 值的时候更改以后线程的 threadLocals(ThreadLocalMap) 中 Entry 对应的 value 值。
理论应用中除了同步办法之外，还有起异步线程解决的场景，这个时候就须要把 ThreadLocal 的内容从父线程传递给子线程，这个怎么办呢？
不急，Java 还有 InheritableThreadLocal 来帮咱们解决这个问题。
2.2 InheritableThreadLoca
public class InheritableThreadLocal<T> extends ThreadLocal<T> {
/**
* Computes the child's initial value for this inheritable thread-local
* variable as a function of the parent's value at the time the child
* thread is created. This method is called from within the parent
* thread before the child is started.
* <p>
* This method merely returns its input argument, and should be overridden
* if a different behavior is desired.
*
* @param parentValue the parent thread's value
* @return the child thread's initial value
*/
protected T childValue(T parentValue) {return parentValue;}
/**
* Get the map associated with a ThreadLocal.
*
* @param t the current thread
*/
ThreadLocalMap getMap(Thread t) {return t.inheritableThreadLocals;}
/**
* Create the map associated with a ThreadLocal.
*
* @param t the current thread
* @param firstValue value for the initial entry of the table.
*/
void createMap(Thread t, T firstValue) {t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
}
}- java.lang.Thread#init(java.lang.ThreadGroup, java.lang.Runnable, java.lang.String, long, java.security.AccessControlContext, boolean）
if (inheritThreadLocals && parent.inheritableThreadLocals != null)
this.inheritableThreadLocals =
ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);- InheritableThreadLocal 操作的是 inheritableThreadLocals 这个变量，而不是 ThreadLocal 操作的 threadLocals 变量。
- 创立新线程的时候会查看父线程中 parent.inheritableThreadLocals 变量是否为 null，如果不为 null 则复制一份 parent.inheritableThreadLocals 的数据到子线程的 this.inheritableThreadLocals 中去。
- 因为复写了 getMap(Thread) 和 CreateMap() 办法间接操作 inheritableThreadLocals，这样就实现了在子线程中获取父线程 ThreadLocal 值。
当初在应用多线程的时候，都是通过线程池来做的，这个时候用 InheritableThreadLocal 能够吗？会有什么问题吗？先看下上面的代码的执行状况：
- test
static InheritableThreadLocal<String> inheritableThreadLocal = new InheritableThreadLocal<>();
public static void main(String[] args) throws InterruptedException {ExecutorService executorService = Executors.newFixedThreadPool(1);
inheritableThreadLocal.set("i am a inherit parent");
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(inheritableThreadLocal.get());
}
});
TimeUnit.SECONDS.sleep(1);
inheritableThreadLocal.set("i am a new inherit parent");// 设置新的值
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(inheritableThreadLocal.get());
}
});
}
i am a inherit parent
i am a inherit parent
public static void main(String[] args) throws InterruptedException {ExecutorService executorService = Executors.newFixedThreadPool(1);
inheritableThreadLocal.set("i am a inherit parent");
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(inheritableThreadLocal.get());
inheritableThreadLocal.set("i am a old inherit parent");// 子线程中设置新的值
}
});
TimeUnit.SECONDS.sleep(1);
inheritableThreadLocal.set("i am a new inherit parent");// 主线程设置新的值
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(inheritableThreadLocal.get());
}
});
}
i am a inherit parent
i am a old inherit parent这里看第一个执行后果，发现主线程第二次设置的值，没有改掉，还是第一次设置的值“i am a inherit parent”，这是什么起因呢？
再看第二个例子的执行后果，发现在第一个工作中设置的“i am a old inherit parent” 的值，在第二个工作中打印进去了。这又是什么起因呢？
回过头来看看下面的源码，在线程池的状况下，第一次创立线程的时候会从父线程中 copy inheritableThreadLocals 中的数据，所以第一个工作胜利拿到了父线程设置的”i am a inherit parent“，第二个工作执行的时候复用了第一个工作的线程，并不会触发复制父线程中的 inheritableThreadLocals 操作，所以即便在主线程中设置了新的值，也会不失效。同时 get() 办法是间接操作 inheritableThreadLocals 这个变量的，所以就间接拿到了第一个工作设置的值。
那遇到线程池应该怎么办呢？
2.3 TransmittableThreadLocal
TransmittableThreadLocal（TTL）这个时候就派上用场了。这是阿里开源的一个组件，咱们来看看它怎么解决线程池的问题，先来一段代码，在下面的根底上批改一下，应用 TransmittableThreadLocal。
static TransmittableThreadLocal<String> transmittableThreadLocal = new TransmittableThreadLocal<>();// 应用 TransmittableThreadLocal
public static void main(String[] args) throws InterruptedException {ExecutorService executorService = Executors.newFixedThreadPool(1);
executorService = TtlExecutors.getTtlExecutorService(executorService); // 用 TtlExecutors 装璜线程池
transmittableThreadLocal.set("i am a transmittable parent");
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(transmittableThreadLocal.get());
transmittableThreadLocal.set("i am a old transmittable parent");// 子线程设置新的值
}
});
System.out.println(transmittableThreadLocal.get());
TimeUnit.SECONDS.sleep(1);
transmittableThreadLocal.set("i am a new transmittable parent");// 主线程设置新的值
executorService.execute(new Runnable() {
@Override
public void run() {System.out.println(transmittableThreadLocal.get());
}
});
}
i am a transmittable parent
i am a transmittable parent
i am a new transmittable parent执行代码后发现，应用 TransmittableThreadLocalTtlExecutors.getTtlExecutorService(executorService) 装璜线程池之后，在每次调用工作的时，都会将以后的主线程的 TransmittableThreadLocal 数据 copy 到子线程外面，执行实现后，再革除掉。同时子线程外面的批改回到主线程时其实并没有失效。这样能够保障每次工作执行的时候都是互不干涉的。这是怎么做到的呢？来看源码。
- TtlExecutors 和 TransmittableThreadLocal 源码
private TtlRunnable(Runnable runnable, boolean releaseTtlValueReferenceAfterRun) {this.capturedRef = new AtomicReference<Object>(capture());
this.runnable = runnable;
this.releaseTtlValueReferenceAfterRun = releaseTtlValueReferenceAfterRun;
}
com.alibaba.ttl.TtlRunnable#run
/**
* wrap method {@link Runnable#run()}.
*/
@Override
public void run() {Object captured = capturedRef.get();// 获取线程的 ThreadLocalMap
if (captured == null || releaseTtlValueReferenceAfterRun && !capturedRef.compareAndSet(captured, null)) {throw new IllegalStateException("TTL value reference is released after run!");
}
Object backup = replay(captured);// 暂存以后子线程的 ThreadLocalMap 到 backup
try {runnable.run();
} finally {restore(backup);// 复原线程执行时被改版的 Threadlocal 对应的值
}
}
com.alibaba.ttl.TransmittableThreadLocal.Transmitter#replay
/**
* Replay the captured {@link TransmittableThreadLocal} values from {@link #capture()},
* and return the backup {@link TransmittableThreadLocal} values in current thread before replay.
*
* @param captured captured {@link TransmittableThreadLocal} values from other thread from {@link #capture()}
* @return the backup {@link TransmittableThreadLocal} values before replay
* @see #capture()
* @since 2.3.0
*/
public static Object replay(Object captured) {@SuppressWarnings("unchecked")
Map<TransmittableThreadLocal<?>, Object> capturedMap = (Map<TransmittableThreadLocal<?>, Object>) captured;
Map<TransmittableThreadLocal<?>, Object> backup = new HashMap<TransmittableThreadLocal<?>, Object>();
for (Iterator<? extends Map.Entry<TransmittableThreadLocal<?>, ?>> iterator = holder.get().entrySet().iterator();
iterator.hasNext();) {Map.Entry<TransmittableThreadLocal<?>, ?> next = iterator.next();
TransmittableThreadLocal<?> threadLocal = next.getKey();
// backup
backup.put(threadLocal, threadLocal.get());
// clear the TTL value only in captured
// avoid extra TTL value in captured, when run task.
if (!capturedMap.containsKey(threadLocal)) {iterator.remove();
threadLocal.superRemove();}
}
// set value to captured TTL
for (Map.Entry<TransmittableThreadLocal<?>, Object> entry : capturedMap.entrySet()) {@SuppressWarnings("unchecked")
TransmittableThreadLocal<Object> threadLocal = (TransmittableThreadLocal<Object>) entry.getKey();
threadLocal.set(entry.getValue());
}
// call beforeExecute callback
doExecuteCallback(true);
return backup;
}
com.alibaba.ttl.TransmittableThreadLocal.Transmitter#restore
/**
* Restore the backup {@link TransmittableThreadLocal} values from {@link Transmitter#replay(Object)}.
*
* @param backup the backup {@link TransmittableThreadLocal} values from {@link Transmitter#replay(Object)}
* @since 2.3.0
*/
public static void restore(Object backup) {@SuppressWarnings("unchecked")
Map<TransmittableThreadLocal<?>, Object> backupMap = (Map<TransmittableThreadLocal<?>, Object>) backup;
// call afterExecute callback
doExecuteCallback(false);
for (Iterator<? extends Map.Entry<TransmittableThreadLocal<?>, ?>> iterator = holder.get().entrySet().iterator();
iterator.hasNext();) {Map.Entry<TransmittableThreadLocal<?>, ?> next = iterator.next();
TransmittableThreadLocal<?> threadLocal = next.getKey();
// clear the TTL value only in backup
// avoid the extra value of backup after restore
if (!backupMap.containsKey(threadLocal)) {iterator.remove();
threadLocal.superRemove();}
}
// restore TTL value
for (Map.Entry<TransmittableThreadLocal<?>, Object> entry : backupMap.entrySet()) {@SuppressWarnings("unchecked")
TransmittableThreadLocal<Object> threadLocal = (TransmittableThreadLocal<Object>) entry.getKey();
threadLocal.set(entry.getValue());
}
}能够看下整个过程的残缺时序图：
OK，既然问题都解决了，来看看理论应用吧，有两种应用，先看第一种，波及 HTTP 申请、Dubbo 申请和 job，采纳的是数据级别的隔离。
三、TTL 在海内商城的理论利用
3.1 不分库，分数据行 + SpringMVC
用户 HTTP 申请，首先咱们要从 url 或者 cookie 中解析出国家编号，而后在 TransmittableThreadLocal 中寄存国家信息，在 MyBatis 的拦截器中读取国家数据，进行 sql 革新，最终操作指定的国家数据，多线程场景下用 TtlExecutors 包装原有自定义线程池，保障在应用线程池的时候可能正确将国家信息传递上来。
- HTTP 申请
public class ShopShardingHelperUtil {private static TransmittableThreadLocal<String> countrySet = new TransmittableThreadLocal<>();
/**
* 获取 threadLocal 中设置的国家标记
* @return
*/
public static String getCountry() {return countrySet.get();
}
/**
* 设置 threadLocal 中设置的国家
*/
public static void setCountry (String country) {countrySet.set(country.toLowerCase());
}
/**
* 革除标记
*/
public static void clear () {countrySet.remove();
}
}
/** 拦截器对 cookie 和 url 综合判断国家信息，放入到 TransmittableThreadLocal 中 **/
// 设置线程中的国家标记
String country = localeContext.getLocale().getCountry().toLowerCase();
ShopShardingHelperUtil.setCountry(country);
/** 自定义线程池，用 TtlExecutors 包装原有自定义线程池 **/
public static Executor getExecutor() {if (executor == null) {synchronized (TransmittableExecutor.class) {if (executor == null) {executor = TtlExecutors.getTtlExecutor(initExecutor());// 用 TtlExecutors 装璜 Executor，联合 TransmittableThreadLocal 解决异步线程 threadlocal 传递问题
}
}
}
return executor;
}
/** 理论应用线程池的中央, 间接调用执行即可 **/
TransmittableExecutor.getExecutor().execute(new BatchExeRunnable(param1,param2));
/** mybatis 的 Interceptor 代码, 应用 TransmittableThreadLocal 的国家信息，革新原有 sql，加上国家参数，在增删改查 sql 中辨别国家数据 **/
public Object intercept(Invocation invocation) throws Throwable {StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
BoundSql boundSql = statementHandler.getBoundSql();
String originalSql = boundSql.getSql();
Statement statement = (Statement) CCJSqlParserUtil.parse(originalSql);
String threadCountry = ShopShardingHelperUtil.getCountry();
// 线程中的国家不为空才进行解决
if (StringUtils.isNotBlank(threadCountry)) {if (statement instanceof Select) {Select selectStatement = (Select) statement;
VivoSelectVisitor vivoSelectVisitor = new VivoSelectVisitor(threadCountry);
vivoSelectVisitor.init(selectStatement);
} else if (statement instanceof Insert) {Insert insertStatement = (Insert) statement;
VivoInsertVisitor vivoInsertVisitor = new VivoInsertVisitor(threadCountry);
vivoInsertVisitor.init(insertStatement);
} else if (statement instanceof Update) {Update updateStatement = (Update) statement;
VivoUpdateVisitor vivoUpdateVisitor = new VivoUpdateVisitor(threadCountry);
vivoUpdateVisitor.init(updateStatement);
} else if (statement instanceof Delete) {Delete deleteStatement = (Delete) statement;
VivoDeleteVisitor vivoDeleteVisitor = new VivoDeleteVisitor(threadCountry);
vivoDeleteVisitor.init(deleteStatement);
}
Field boundSqlField = BoundSql.class.getDeclaredField("sql");
boundSqlField.setAccessible(true);
boundSqlField.set(boundSql, statement.toString());
} else {logger.error("----------- intercept not-add-country sql.... ---------" + statement.toString());
}
logger.info("----------- intercept query new sql.... ---------" + statement.toString());
// 调用办法，实际上就是拦挡的办法
Object result = invocation.proceed();
return result;
}对于 Dubbo 接口和无奈判断国家信息的 HTTP 接口，在入参局部减少国家信息参数，通过拦截器或者手动 set 国家信息到 TransmittableThreadLocal。
对于定时工作 job，因为所有国家都须要执行，所以会把所有国家进行遍历执行，这也能够通过简略的注解来解决。
这个版本的革新，点检测试也根本通过了，自动化脚本验证也是没问题的，不过因为业务倒退问题最终没上线。
3.2 分库 + SpringBoot
后续在建设新的国家商城的时候，分库分表计划调整为每个国家独立数据库，同时整体开发框架降级到 SpringBoot，咱们把这套计划做了降级，总体思路是一样的，只是在实现细节上略有不同。
SpringBoot 外面的异步个别通过 @Async 这个注解来实现，通过自定义线程池来包装，应用时在 HTTP 申请判断 locale 信息的写入国家信息，后续实现切 DB 的操作。
对于 Dubbo 接口和无奈判断国家信息的 HTTP 接口，在入参局部减少国家信息参数，通过拦截器或者手动 set 国家信息到 TransmittableThreadLocal。
@Bean
public ThreadPoolTaskExecutor threadPoolTaskExecutor(){return TtlThreadPoolExecutors.getAsyncExecutor();
}
public class TtlThreadPoolExecutors {
private static final String COMMON_BUSINESS = "COMMON_EXECUTOR";
public static final int QUEUE_CAPACITY = 20000;
public static ExecutorService getExecutorService() {return TtlExecutorServiceMananger.getExecutorService(COMMON_BUSINESS);
}
public static ExecutorService getExecutorService(String threadGroupName) {return TtlExecutorServiceMananger.getExecutorService(threadGroupName);
}
public static ThreadPoolTaskExecutor getAsyncExecutor() {
// 用 TtlExecutors 装璜 Executor，联合 TransmittableThreadLocal 解决异步线程 threadlocal 传递问题
return getTtlThreadPoolTaskExecutor(initTaskExecutor());
}
private static ThreadPoolTaskExecutor initTaskExecutor () {return initTaskExecutor(TtlThreadPoolFactory.DEFAULT_CORE_SIZE, TtlThreadPoolFactory.DEFAULT_POOL_SIZE, QUEUE_CAPACITY);
}
private static ThreadPoolTaskExecutor initTaskExecutor (int coreSize, int poolSize, int executorQueueCapacity) {ThreadPoolTaskExecutor taskExecutor = new ThreadPoolTaskExecutor();
taskExecutor.setCorePoolSize(coreSize);
taskExecutor.setMaxPoolSize(poolSize);
taskExecutor.setQueueCapacity(executorQueueCapacity);
taskExecutor.setKeepAliveSeconds(120);
taskExecutor.setAllowCoreThreadTimeOut(true);
taskExecutor.setThreadNamePrefix("TaskExecutor-ttl");
taskExecutor.initialize();
return taskExecutor;
}
private static ThreadPoolTaskExecutor getTtlThreadPoolTaskExecutor(ThreadPoolTaskExecutor executor) {if (null == executor || executor instanceof ThreadPoolTaskExecutorWrapper) {return executor;}
return new ThreadPoolTaskExecutorWrapper(executor);
}
}
/**
* @ClassName : LocaleContextHolder
* @Description : 本地化信息上下文 holder
*/
public class LocalizationContextHolder {private static TransmittableThreadLocal<LocalizationContext> localizationContextHolder = new TransmittableThreadLocal<>();
private static LocalizationInfo defaultLocalizationInfo = new LocalizationInfo();
private LocalizationContextHolder(){}
public static LocalizationContext getLocalizationContext() {return localizationContextHolder.get();
}
public static void resetLocalizationContext () {localizationContextHolder.remove();
}
public static void setLocalizationContext (LocalizationContext localizationContext) {if(localizationContext == null) {resetLocalizationContext();
} else {localizationContextHolder.set(localizationContext);
}
}
public static void setLocalizationInfo (LocalizationInfo localizationInfo) {LocalizationContext localizationContext = getLocalizationContext();
String brand = (localizationContext instanceof BrandLocalizationContext ?
((BrandLocalizationContext) localizationContext).getBrand() : null);
if(StringUtils.isNotEmpty(brand)) {localizationContext = new SimpleBrandLocalizationContext(localizationInfo, brand);
} else if(localizationInfo != null) {localizationContext = new SimpleLocalizationContext(localizationInfo);
} else {localizationContext = null;}
setLocalizationContext(localizationContext);
}
public static void setDefaultLocalizationInfo(@Nullable LocalizationInfo localizationInfo) {LocalizationContextHolder.defaultLocalizationInfo = localizationInfo;}
public static LocalizationInfo getLocalizationInfo () {LocalizationContext localizationContext = getLocalizationContext();
if(localizationContext != null) {LocalizationInfo localizationInfo = localizationContext.getLocalizationInfo();
if(localizationInfo != null) {return localizationInfo;}
}
return defaultLocalizationInfo;
}
public static String getCountry(){return getLocalizationInfo().getCountry();}
public static String getTimezone(){return getLocalizationInfo().getTimezone();}
public static String getBrand(){return getBrand(getLocalizationContext());
}
public static String getBrand(LocalizationContext localizationContext) {if(localizationContext == null) {return null;}
if(localizationContext instanceof BrandLocalizationContext) {return ((BrandLocalizationContext) localizationContext).getBrand();}
throw new LocaleException("unsupported localizationContext type");
}
}
@Override
public LocaleContext resolveLocaleContext(final HttpServletRequest request) {parseLocaleCookieIfNecessary(request);
LocaleContext localeContext = new TimeZoneAwareLocaleContext() {
@Override
public Locale getLocale() {return (Locale) request.getAttribute(LOCALE_REQUEST_ATTRIBUTE_NAME);
}
@Override
public TimeZone getTimeZone() {return (TimeZone) request.getAttribute(TIME_ZONE_REQUEST_ATTRIBUTE_NAME);
}
};
// 设置线程中的国家标记
setLocalizationInfo(request, localeContext.getLocale());
return localeContext;
}
private void setLocalizationInfo(HttpServletRequest request, Locale locale) {String country = locale!=null?locale.getCountry():null;
String language = locale!=null?(locale.getLanguage() + "_" + locale.getVariant()):null;
LocaleRequestMessage localeRequestMessage = localeRequestParser.parse(request);
final String countryStr = country;
final String languageStr = language;
final String brandStr = localeRequestMessage.getBrand();
LocalizationContextHolder.setLocalizationContext(new BrandLocalizationContext() {
@Override
public String getBrand() {return brandStr;}
@Override
public LocalizationInfo getLocalizationInfo() {return LocalizationInfoAssembler.assemble(countryStr, languageStr);
}
});
}对于定时工作 job，因为所有国家都须要执行，所以会把所有国家进行遍历执行，这也能够通过简略的注解和 AOP 来解决。
四、总结
本文从业务拓展的角度论述了在简单业务场景下如何通过 ThreadLocal，过渡到 InheritableThreadLocal，再通过 TransmittableThreadLocal 解决理论业务问题。因为海内的业务在一直的摸索中后退，技术也在一直的摸索中演进，面对这种复杂多变的状况，咱们的应答策略是先做国际化，再做本地化，more global 能力 more local，多国家的隔离只是国际化最根本的终点，将来还有很多业务和技术等着咱们去挑战。
作者：vivo 官网商城开发团队
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