ThreadLocal InheritableThreadLocal TransmittableThreadLocal简单使用

需求: 主线程向异步线程传递用户token信息,

关于线程之间数据传递的几个关键对象,

• 主线程向子线程传递时,可以通过InheritableThreadLocal对象
• 使用ExecutorService或者CompletableFuture执行时, 线程池内线程复用的原因,同时Thread对象内的inheritableThreadLocals值一是null,所以无法使用InheritableThreadLocal对象
• TransmittableThreadLocal为比较适合解决方案 官方地址
• 异步线程RequestContextHolder为空问题

先上例子

public static final ThreadLocal<String> context = new ThreadLocal<>();//
public static final ThreadLocal<String> context1 = new TransmittableThreadLocal<>();//
public static final ThreadLocal<String> context2 = new InheritableThreadLocal<>();

public static void main(String[] args) {
        context.set("A");
        context1.set("B");
        context2.set("C");
        CompletableFuture.runAsync(() -> {//ThreadLocal 线程之间隔离
            String mm = context.get();
            log.info("1: {}",mm);
        });
        CompletableFuture.runAsync(TtlRunnable.get(() -> { //TransmittableThreadLocal可以取到
            String mm = context1.get();
            log.info("2: {}",mm);

        }));
        CompletableFuture.runAsync(() -> { //取不到
            String mm = context2.get();
            log.info("3: {}",mm);

        });
        Thread thread = new Thread(() -> { // 子线程,正常可以取到
            String mm = context2.get();
            log.info("4: {}",mm);
        });
        thread.start();
    }
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[ForkJoinPool.commonPool-worker-1] INFO cn.me56.integration.stat.StatApiController - 1: null
[ForkJoinPool.commonPool-worker-2] INFO cn.me56.integration.stat.StatApiController - 2: A
[ForkJoinPool.commonPool-worker-1] INFO cn.me56.integration.stat.StatApiController - 3: null
[Thread-0] INFO cn.me56.integration.stat.StatApiController - 4: C
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这里是InheritableThreadLocal使用子线程的例子:

public class InheritableThreadLocalDemo {

    private static ThreadLocal<String> threadLocal = new InheritableThreadLocal<>();

    public static void main(String[] args) {
        threadLocal.set("mainThread");
        System.out.println("value:"+threadLocal.get());
        Thread thread = new Thread(new Runnable() { //子线程,可以取到
            @Override
            public void run() {
                String value = threadLocal.get();
                System.out.println("value:"+value);
            }
        });
        thread.start();
    }

}
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value:mainThread
value:mainThread
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TransmittableThreadLocal,简单使用方法

public static final ThreadLocal<String> context1 = new TransmittableThreadLocal<>();//
CompletableFuture.runAsync(TtlRunnable.get(() -> { 
	//do something...
}));
或者
CompletableFuture.supplyAsync(TtlWrappers.wrapSupplier(()-> {
	//do something...
	return "return value";
	}) );
或者
java agent 方式 
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线程之间可以传递数据之后,再看下RequestContextHolder为空问题, 初步是想把request对象传给异步线程, 尝试之后觉得此方案不合理,没必要把整个request传进去

1. 使用如下方式.设置之后,进入异步线程,RequestContextHolder.getRequestAttributes()也还是空的…

RequestContextHolder.setRequestAttributes(RequestContextHolder.getRequestAttributes(), true);
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2. 如下使用如下方式.在主线程关闭之后,子线程想获取request内参数,还是空的,如果是copy一个request,应该就能正常了

CompletableFuture.runAsync(() -> { 
	RequestContextHolder.setRequestAttributes(...);
	//do something...
});
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最终,因为业务需要完成的,是希望把长时间统计/查询接口,在系统资源有限的情况下,以时间换空间,拆分成多个子任务,所以这里线程之间传参仅仅只用了MDC.put/get方式简单实现了一下