java.lang
Class ThreadLocal
java.lang.Object
|
+--java.lang.ThreadLocal
public class
ThreadLocalextends
Object ThreadLocal objects have a different state associated with every
Thread that accesses them. Every access to the ThreadLocal object
(through the
get()
and
set()
methods)
only affects the state of the object as seen by the currently
executing Thread.
The first time a ThreadLocal object is accessed on a particular
Thread, the state for that Thread's copy of the local variable is set by
executing the method initialValue()
.
An example how you can use this:
class Connection
{
private static ThreadLocal owner = new ThreadLocal()
{
public Object initialValue()
{
return("nobody");
}
};
...
}
Now all instances of connection can see who the owner of the currently
executing Thread is by calling
owner.get()
. By default any
Thread would be associated with 'nobody'. But the Connection object could
offer a method that changes the owner associated with the Thread on
which the method was called by calling
owner.put("somebody")
.
(Such an owner changing method should then be guarded by security checks.)
When a Thread is garbage collected all references to values of
the ThreadLocal objects associated with that Thread are removed.
Since:Authors:- Mark Wielaard <mark@klomp.org>
- Eric Blake <ebb9@email.byu.edu>
ThreadLocal
public ThreadLocal()
Creates a ThreadLocal object without associating any value to it yet.
get
public Object get()
Gets the value associated with the ThreadLocal object for the currently
executing Thread. If this is the first time the current thread has called
get(), and it has not already called set(), the value is obtained by
initialValue()
.
Returns:
- the value of the variable in this thread
initialValue
protected Object initialValue()
Called once per thread on the first invocation of get(), if set() was
not already called. The default implementation returns null
.
Often, this method is overridden to create the appropriate initial object
for the current thread's view of the ThreadLocal.
Returns:
- the initial value of the variable in this thread
set
public void set(java.lang.Object value)
Sets the value associated with the ThreadLocal object for the currently
executing Thread. This overrides any existing value associated with the
current Thread and prevents initialValue()
from being
called if this is the first access to this ThreadLocal in this Thread.
Parameters:
get()
andset()
methods) only affects the state of the object as seen by the currently executing Thread.The first time a ThreadLocal object is accessed on a particular Thread, the state for that Thread's copy of the local variable is set by executing the method
initialValue()
.An example how you can use this:
Now all instances of connection can see who the owner of the currently executing Thread is by callingowner.get()
. By default any Thread would be associated with 'nobody'. But the Connection object could offer a method that changes the owner associated with the Thread on which the method was called by callingowner.put("somebody")
. (Such an owner changing method should then be guarded by security checks.)When a Thread is garbage collected all references to values of the ThreadLocal objects associated with that Thread are removed.