implement ThreadLocal integration #130

src/main/java/com/alibaba/ttl/TtlCopier.java

+package com.alibaba.ttl;
+
+/**
+ * TtlCopier creates the value when {@link TransmittableThreadLocal.Transmitter#capture()},
+ * use the created value when {@link TransmittableThreadLocal.Transmitter#replay(Object)}
+ *
+ * @see TransmittableThreadLocal.Transmitter
+ * @see TransmittableThreadLocal.Transmitter#capture()
+ * @author Jerry Lee (oldratlee at gmail dot com)
+ * @since 2.11.0
+ */
+public interface TtlCopier<T> {
+    /**
+     * Computes the value for {@link TransmittableThreadLocal}
+     * or registered {@link ThreadLocal}(registered by {@link TransmittableThreadLocal.Transmitter#registerThreadLocal})
+     * as a function of the source thread's value at the time the task
+     * Object is created.
+     * <p>
+     * This method is called from {@link TtlRunnable} or
+     * {@link TtlCallable} when it create, before the task is started
+     * (aka. called when {@link TransmittableThreadLocal.Transmitter#capture()}).
+     *
+     * @see TransmittableThreadLocal.Transmitter#registerThreadLocal(ThreadLocal, TtlCopier)
+     * @see TransmittableThreadLocal.Transmitter#registerThreadLocalWithShadowCopier(ThreadLocal)
+     * @see TransmittableThreadLocal.Transmitter#unregisterThreadLocal
+     */
+    T copy(T parentValue);
+}