java.lang
Class InheritableThreadLocal

java.lang.Object
  |
  +--java.lang.ThreadLocal
        |
        +--java.lang.InheritableThreadLocal

public class InheritableThreadLocal

extends ThreadLocal

This class extends ThreadLocal to provide inheritance of values from parent Thread to child Thread: when a child thread is created, the child receives initial values for all InheritableThreadLocals for which the parent has values. Normally the child's values will be identical to the parent's; however, the child's value can be made an arbitrary function of the parent's by overriding the childValue method in this class.

InheritableThreadLocal variables are used in preference to ordinary ThreadLocal variables when the per-thread-attribute being maintained in the variable (e.g., User ID, Transaction ID) must be automatically transmitted to any child threads that are created.

Since:

1.2

See Also:

ThreadLocal

Constructor Summary

InheritableThreadLocal()
Creates an InheritableThreadLocal variable.

Method Summary

protected Object	childValue(Object parentValue) Computes the child's initial value for this InheritableThreadLocal as a function of the parent's value at the time the child Thread is created.
Object	get() Returns the value in the calling thread's copy of this ThreadLocal variable.
void	set(Object value) Sets the calling thread's instance of this ThreadLocal variable to the given value.

Methods inherited from class java.lang.ThreadLocal

initialValue

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

InheritableThreadLocal

public InheritableThreadLocal()

Creates an InheritableThreadLocal variable.

Method Detail

get

public Object get()

Returns the value in the calling thread's copy of this ThreadLocal variable. Creates and initializes the copy if this is the first time the thread has called this method.

Overrides:

get in class ThreadLocal

Following copied from class: java.lang.ThreadLocal

Returns:

the value of this ThreadLocal

set

public void set(Object value)

Sets the calling thread's instance of this ThreadLocal variable to the given value. This is only used to change the value from the one assigned by the initialValue method, and many applications will have no need for this functionality.

Overrides:

set in class ThreadLocal

Parameters:

value - the value to be stored in the calling threads' copy of this ThreadLocal.

childValue

protected Object childValue(Object parentValue)

Computes the child's initial value for this InheritableThreadLocal 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.

This method merely returns its input argument, and should be overridden if a different behavior is desired.

Parameters:

parentValue - the parent thread's value

Returns:

the child thread's initial value