spring boot @Async异步注解上下文透传
上一篇文章说到，之前使用了@Async注解，子线程无法获取到上下文信息，导致流量无法打到灰度，然后改成 线程池的方式，每次调用异步调用的时候都手动透传 上下文（硬编码）解决了问题。
后面查阅了资料，找到了方案不用每次硬编码，来上下文透传数据了。
方案一：
继承线程池，重写相应的方法，透传上下文。
方案二：（推荐）
线程池ThreadPoolTaskExecutor，有一个TaskDecorator装饰器，实现这个接口，透传上下文。
方案一：继承线程池，重写相应的方法，透传上下文。
1、ThreadPoolTaskExecutor spring封装的线程池
ThreadPoolTaskExecutor 线程池代码如下：
@Bean(ExecutorConstant.simpleExecutor_3)
public Executor asyncExecutor3() {
MyThreadPoolTaskExecutor taskExecutor = new MyThreadPoolTaskExecutor();
taskExecutor.setCorePoolSize(corePoolSize);
taskExecutor.setMaxPoolSize(maxPoolSize);
taskExecutor.setQueueCapacity(queueCapacity);
taskExecutor.setThreadNamePrefix(threadNamePrefix_3);
taskExecutor.initialize();
return taskExecutor;
}
//------- 继承父类 重写对应的方法 start
class MyCallable<T> implements Callable<T> {
private Callable<T> task;
private RequestAttributes context;
public MyCallable(Callable<T> task, RequestAttributes context) {
this.task = task;
this.context = context;
}
@Override
public T call() throws Exception {
if (context != null) {
RequestContextHolder.setRequestAttributes(context);
}
try {
return task.call();
} finally {
RequestContextHolder.resetRequestAttributes();
}
}
}
class MyThreadPoolTaskExecutor extends ThreadPoolTaskExecutor{
@Override
public <T> Future<T> submit(Callable<T> task) {
return super.submit(new MyCallable(task, RequestContextHolder.currentRequestAttributes()));
}
@Override
public <T> ListenableFuture<T> submitListenable(Callable<T> task) {
return super.submitListenable(new MyCallable(task, RequestContextHolder.currentRequestAttributes()));
}
}
//------- 继承父类 重写对应的方法 end
1、MyCallable是继承Callable，创建MyCallable对象的时候已经把Attributes对象赋值给属性context了（创建MyCallable对象的时候因为实在当前主线程创建的，所以是能获取到请求的Attributes），在执行call方法前，先执行了RequestContextHolder.setRequestAttributes(context); 【把这个MyCallable对象的属性context 设置到setRequestAttributes中】 所以在执行具体业务时，当前线程（子线程）就能取得主线程的Attributes
2、MyThreadPoolTaskExecutor类是继承了ThreadPoolTaskExecutor 重写了submit和submitListenable方法
为什么是重写submit和submitListenable这两个方法了？
@Async AOP源码的方法位置是在：AsyncExecutionInterceptor.invoke
doSubmit方法能看出来
无返回值调用的是线程池方法：submit()
有返回值，根据不同的返回类型也知道：
- 返回值类型是：Future.class 调用的是方法：submit()
- 返回值类型是：ListenableFuture.class 调用的方法是：submitListenable(task)
- 返回值类型是：CompletableFuture.class调用的是CompletableFuture.supplyAsync这个在异步注解中暂时用不上的，就不考虑重写了。
public Object invoke(final MethodInvocation invocation) throws Throwable {
Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
if (executor == null) {
throw new IllegalStateException(
"No executor specified and no default executor set on AsyncExecutionInterceptor either");
}
Callable<Object> task = () -> {
try {
Object result = invocation.proceed();
if (result instanceof Future) {
return ((Future<?>) result).get();
}
}
catch (ExecutionException ex) {
handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
}
catch (Throwable ex) {
handleError(ex, userDeclaredMethod, invocation.getArguments());
}
return null;
};
return doSubmit(task, executor, invocation.getMethod().getReturnType());
}
@Nullable
protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
if (CompletableFuture.class.isAssignableFrom(returnType)) {
return CompletableFuture.supplyAsync(() -> {
try {
return task.call();
}
catch (Throwable ex) {
throw new CompletionException(ex);
}
}, executor);
}
else if (ListenableFuture.class.isAssignableFrom(returnType)) {
return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
}
else if (Future.class.isAssignableFrom(returnType)) {
return executor.submit(task);
}
else {
executor.submit(task);
return null;
}
}
2、ThreadPoolExecutor 原生线程池
ThreadPoolExecutor线程池代码如下：
//------- ThreadPoolExecutor 继承父类 重写对应的方法 start
class MyRunnable implements Runnable {
private Runnable runnable;
private RequestAttributes context;
public MyRunnable(Runnable runnable, RequestAttributes context) {
this.runnable = runnable;
this.context = context;
}
@Override
public void run() {
if (context != null) {
RequestContextHolder.setRequestAttributes(context);
}
try {
runnable.run();
} finally {
RequestContextHolder.resetRequestAttributes();
}
}
}
class MyThreadPoolExecutor extends ThreadPoolExecutor{
@Override
public void execute(Runnable command) {
if(!(command instanceof MyRunnable)){
command = new MyRunnable(command,RequestContextHolder.currentRequestAttributes())
}
super.execute(command);
}
public MyThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
public MyThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory);
}
public MyThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, RejectedExecutionHandler handler) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);
}
public MyThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, threadFactory, handler);
}
}
//------- ThreadPoolExecutor 继承父类 重写对应的方法 end
像ThreadPoolExecutor主要重写execute方法，在启动新线程的时候先把Attributes取到放到MyRunnable对象的一个属性中，MyRunnable在具体执行run方法的时候，把属性Attributes赋值到子线程中，当run方法执行完了在把Attributes清空掉。
为什么只要重写了execute方法就可以了？
ThreadPoolExecutor大家都知道主要是由submit和execute方法来执行的。
看ThreadPoolExecutor类的submit具体执行方法是由父类AbstractExecutorService#submit来实现。
具体代码在下面贴出来了，可以看到submit实际上最后调用的还是execute方法，所以我们重写execute方法就好了。
submit方法路径及源码：
java.util.concurrent.AbstractExecutorService#submit(java.lang.Runnable)
public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerException();
RunnableFuture<Void> ftask = newTaskFor(task, null);
execute(ftask);
return ftask;
}
/**
* @throws RejectedExecutionException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public <T> Future<T> submit(Runnable task, T result) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task, result);
execute(ftask);
return ftask;
}
/**
* @throws RejectedExecutionException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public <T> Future<T> submit(Callable<T> task) {
if (task == null) throw new NullPointerException();
RunnableFuture<T> ftask = newTaskFor(task);
execute(ftask);
return ftask;
}
方案二：（推荐）
ThreadPoolTaskExecutor线程池
实现TaskDecorator接口,把实现类设置到taskExecutor.setTaskDecorator(new MyTaskDecorator());
//------- 实现TaskDecorator 接口 start
@Bean(ExecutorConstant.simpleExecutor_4)
public Executor asyncExecutor4() {
MyThreadPoolTaskExecutor taskExecutor = new MyThreadPoolTaskExecutor();
taskExecutor.setCorePoolSize(corePoolSize);
taskExecutor.setMaxPoolSize(maxPoolSize);
taskExecutor.setQueueCapacity(queueCapacity);
taskExecutor.setThreadNamePrefix(threadNamePrefix_4);
taskExecutor.setTaskDecorator(new MyTaskDecorator());
taskExecutor.initialize();
return taskExecutor;
}
class MyTaskDecorator implements TaskDecorator{
@Override
public Runnable decorate(Runnable runnable) {
try {
RequestAttributes attributes = RequestContextHolder.getRequestAttributes();
return () -> {
try {
RequestContextHolder.setRequestAttributes(attributes);
runnable.run();
} finally {
RequestContextHolder.resetRequestAttributes();
}
};
} catch (IllegalStateException e) {
return runnable;
}
}
}
//------- 实现TaskDecorator 接口 end
为什么设置了setTaskDecorator就能实现透传数据了？
主要还是看taskExecutor.initialize()方法，主要是重写了ThreadPoolExecutor的execute方法，用装饰器模式 增强了Runnable接口，源代码如下：
@Nullable
private ThreadPoolExecutor threadPoolExecutor;
//初始化方法
public void initialize() {
if (logger.isDebugEnabled()) {
logger.debug("Initializing ExecutorService" + (this.beanName != null ? " '" + this.beanName + "'" : ""));
}
if (!this.threadNamePrefixSet && this.beanName != null) {
setThreadNamePrefix(this.beanName + "-");
}
this.executor = initializeExecutor(this.threadFactory, this.rejectedExecutionHandler);
}
@Override
protected ExecutorService initializeExecutor(
ThreadFactory threadFactory, RejectedExecutionHandler rejectedExecutionHandler) {
BlockingQueue<Runnable> queue = createQueue(this.queueCapacity);
ThreadPoolExecutor executor;
//判断是否设置了，taskDecorator装饰器
if (this.taskDecorator != null) {
executor = new ThreadPoolExecutor(
this.corePoolSize, this.maxPoolSize, this.keepAliveSeconds, TimeUnit.SECONDS,
queue, threadFactory, rejectedExecutionHandler) {
@Override
public void execute(Runnable command) {
//执行装饰器方法包装Runnable接口
Runnable decorated = taskDecorator.decorate(command);
if (decorated != command) {
decoratedTaskMap.put(decorated, command);
}
super.execute(decorated);
}
};
}
else {
executor = new ThreadPoolExecutor(
this.corePoolSize, this.maxPoolSize, this.keepAliveSeconds, TimeUnit.SECONDS,
queue, threadFactory, rejectedExecutionHandler);
}
if (this.allowCoreThreadTimeOut) {
executor.allowCoreThreadTimeOut(true);
}
//把初始化好的ThreadPoolExecutor线程池赋值给 当前类属性threadPoolExecutor
this.threadPoolExecutor = executor;
return executor;
}
总结
无论是方案1还是方案2，原理都是先在当前线程获取到Attributes，然后把Attributes赋值到Runnable的一个属性中，在起一个子线程后，具体执行run方法的时候，把Attributes设置给当子线程，当run方法执行完了，在清空Attributes。
方案2实现比较优雅，所以推荐使用它。
工作没多久的时候觉得spring的使用很麻烦，但是工作久了慢慢发现spring一些小细节、设计模式运用的非常巧妙，很容易解决遇到的问题，只能说spring 🐂🍺。
我已经把上述代码例子放到gitee了，大家感兴趣可以clone 传送门～
人生很多烦恼，是因为想得太多，做得太少
