Package io.micrometer.context

Interface ThreadLocalAccessor<V>

public interface ThreadLocalAccessor<V>

Contract to assist with setting and clearing a ThreadLocal.

Since:

1.0.0

See Also:

• ContextRegistry.registerThreadLocalAccessor(ThreadLocalAccessor)
• ContextRegistry.registerThreadLocalAccessor(String, Supplier, Consumer, Runnable)

Method Summary

Modifier and Type	Method	Description
V	getValue()	Return the current ThreadLocal value.
Object	key()	The key to associate with the ThreadLocal value when saved within a ContextSnapshot.
default void	reset()	Deprecated. To be replaced by calls to setValue() (and/or restore()), which needs to be implemented when this implementation is removed.
default void	restore()	Called instead of restore(Object) when there was no ThreadLocal value existing at the start of the scope.
default void	restore(V previousValue)	Restore the ThreadLocal at the end of a ContextSnapshot.Scope to the previous value it had before the start of the scope.
default void	setValue()	Called instead of setValue(Object) in order to remove the current ThreadLocal value at the start of a ContextSnapshot.Scope.
void	setValue(V value)	Set the ThreadLocal at the start of a ContextSnapshot.Scope to a value obtained from a ContextSnapshot or from a different type of context (through a ContextAccessor).

Method Details

key

Object key()

The key to associate with the ThreadLocal value when saved within a ContextSnapshot.

getValue

@Nullable
V getValue()

Return the current ThreadLocal value.

This method is called in two scenarios:

• When capturing a ContextSnapshot. A null value is ignored and the key() will not be present in the snapshot.
• When setting ThreadLocal values from a ContextSnapshot or from a Context object (through a ContextAccessor) to save existing values in order to restore(Object) them at the end of the scope. A null value means the ThreadLocal should not be set and upon closing a ContextSnapshot.Scope, the restore() variant is called.

setValue

void setValue(V value)

Set the ThreadLocal at the start of a ContextSnapshot.Scope to a value obtained from a ContextSnapshot or from a different type of context (through a ContextAccessor).

Parameters:

value - the value to set, never null when called from a ContextSnapshot implementation, which is not allowed to store mappings to null.

setValue

default void setValue()

Called instead of setValue(Object) in order to remove the current ThreadLocal value at the start of a ContextSnapshot.Scope.

Since:

1.0.3

reset

@Deprecated
default void reset()

Deprecated.

To be replaced by calls to setValue() (and/or restore()), which needs to be implemented when this implementation is removed.

Remove the ThreadLocal value when setting ThreadLocal values in case of missing mapping for a key() from a ContextSnapshot, or a Context object (operated upon by ContextAccessor).

restore

default void restore(V previousValue)

Restore the ThreadLocal at the end of a ContextSnapshot.Scope to the previous value it had before the start of the scope.

Parameters:

previousValue - previous value to set, never null when called from a ContextSnapshot * implementation, which is not allowed to store mappings to null.

Since:

1.0.1

restore

default void restore()

Called instead of restore(Object) when there was no ThreadLocal value existing at the start of the scope.

Since:

1.0.3

See Also:

• getValue()