一、引言
海外商城从印度做起，慢慢的会有一些其他国家的诉求，这个时候需要我们针对当前的商城做一个改造，可以支撑多个国家的商城，这里会涉及多个问题，多语言，多国家，多时区，本地化等等。在多国家的情况下如何把识别出来的国家信息传递下去，一层一层直到代码执行的最后一步。甚至还有一些多线程的场景需要处理。
二、背景技术
2.1 ThreadLocal
ThreadLocal是最容易想到了，入口识别到国家信息后，丢进ThreadLocal，这样后续代码、redis、DB等做国家区分的时候都能使用到。
这里先简单介绍一下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线程都有属于自己的threadLocals(ThreadLocalMap),里面有一个弱引用的Entry(ThreadLocal,Object)。
-
get方法首先通过Thread.currentThread得到当前线程，然后拿到线程的threadLocals(ThreadLocalMap)，再从Entry中取得当前线程存储的value。
-
set值的时候更改当前线程的threadLocals(ThreadLocalMap)中Entry对应的value值。
实际使用中除了同步方法之外，还有起异步线程处理的场景，这个时候就需要把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来帮我们解决这个问题。
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。
- 创建新线程的时候会检查父线程中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()方法直接操作inheritableThreadLocals，这样就实现了在子线程中获取父线程ThreadLocal值。
现在在使用多线程的时候，都是通过线程池来做的，这个时候用InheritableThreadLocal可以吗？会有什么问题吗？先看下下面的代码的执行情况：
-
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
这里看第一个执行结果，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”，这是什么原因呢？
再看第二个例子的执行结果，发现在第一个任务中设置的“i am a old inherit parent"的值，在第二个任务中打印出来了。这又是什么原因呢？
回过头来看看上面的源码，在线程池的情况下，第一次创建线程的时候会从父线程中copy inheritableThreadLocals中的数据，所以第一个任务成功拿到了父线程设置的”i am a inherit parent“，第二个任务执行的时候复用了第一个任务的线程，并不会触发复制父线程中的inheritableThreadLocals操作，所以即使在主线程中设置了新的值，也会不生效。同时get()方法是直接操作inheritableThreadLocals这个变量的，所以就直接拿到了第一个任务设置的值。
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，我们来看看它怎么解决线程池的问题，先来一段代码，在上面的基础上修改一下，使用TransmittableThreadLocal。
-
static TransmittableThreadLocal<String> transmittableThreadLocal =
new TransmittableThreadLocal<>();
// 使用TransmittableThreadLocal
-
-
-
public static void main(String[] args) throws InterruptedException {
-
-
ExecutorService executorService = Executors.newFixedThreadPool(
1);
-
executorService = TtlExecutors.getTtlExecutorService(executorService);
// 用TtlExecutors装饰线程池
-
-
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，使用TransmittableThreadLocalTtlExecutors.getTtlExecutorService(executorService)装饰线程池之后，在每次调用任务的时，都会将当前的主线程的TransmittableThreadLocal数据copy到子线程里面，执行完成后，再清除掉。同时子线程里面的修改回到主线程时其实并没有生效。这样可以保证每次任务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);
// 暂存当前子线程的ThreadLocalMap到backup
-
try {
-
runnable.run();
-
}
finally {
-
restore(backup);
// 恢复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());
-
}
-
}
可以看下整个过程的完整时序图：
OK，既然问题都解决了，来看看实际使用吧，有两种使用，先看第一种，涉及HTTP请求、Dubbo请求和 job，采用的是数据级别的隔离。
三、 TTL 在海外商城的实际应用
3.1 不分库，分数据行 + SpringMVC
用户 HTTP 请求，首先我们要从url或者cookie中解析出国家编号，然后在TransmittableThreadLocal中存放国家信息，在 MyBatis 的拦截器中读取国家数据，进行sql改造，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，保障在使用线程池的时候能够正确将国家信息传递下去。
-
HTTP 请求
-
-
@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装饰Executor，结合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志
-
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 Dubbo 接口和无法判断国家信息的 HTTP 接口，在入参部分增加国家信息参数，通过拦截器或者手动set国家信息到TransmittableThreadLocal。
对于定时任务 job，因为所有国家都需要执行，所以会把所有国家进行遍历执行，这也可以通过简单的注解来解决。
这个版本的改造，点检测试也基本通过了，自动化脚本验证也是没问题的，不过因为业务发展问题最终没上线。
3.2 分库 + SpringBoot
后续在建设新的国家商城的时候，分库分表方案调整为每个国家独立数据库，同时整体开发框架升级到SpringBoot，我们把这套方案做了升级，总体思路是一样的，只是在实现细节上略有不同。
SpringBoot 里面的异步一般通过@Async这个注解来实现，通过自定义线程池来包装，使用时在 HTTP 请求判断locale信息的写入国家信息，后续完成切DB的操作。
对于 Dubbo 接口和无法判断国家信息的 HTTP 接口，在入参部分增加国家信息参数，通过拦截器或者手动set国家信息到TransmittableThreadLocal。
对于定时任务job，因为所有国家都需要执行，所以会把所有国家进行遍历执行，这也可以通过简单的注解和AOP来解决。
四、总结
本文从业务拓展的角度阐述了在复杂业务场景下如何通过ThreadLocal，过渡到InheritableThreadLocal，再通过TransmittableThreadLocal解决实际业务问题。因为海外的业务在不断的探索中前进，技术也在不断的探索中演进，面对这种复杂多变的情况，我们的应对策略是先做国际化，再做本地化，more global才能more local，多国家的隔离只是国际化最基本的起点，未来还有很多业务和技术等着我们去挑战。
作者：vivo 官网商城开发团队
转载：https://blog.csdn.net/vivo_tech/article/details/113500269
查看评论