Added in API level 34

StackWalker

class StackWalker

kotlin.Any
↳	java.lang.StackWalker

A stack walker.

The walk method opens a sequential stream of StackFrames for the current thread and then applies the given function to walk the StackFrame stream. The stream reports stack frame elements in order, from the top most frame that represents the execution point at which the stack was generated to the bottom most frame. The StackFrame stream is closed when the walk method returns. If an attempt is made to reuse the closed stream, IllegalStateException will be thrown.

The stack walking options of a StackWalker determines the information of StackFrame objects to be returned. By default, stack frames of the reflection API and implementation classes are hidden and StackFrames have the class name and method name available but not the Class reference.

StackWalker is thread-safe. Multiple threads can share a single StackWalker object to traverse its own stack. A permission check is performed when a StackWalker is created, according to the options it requests. No further permission check is done at stack walking time.

Summary

Nested classes
	Option Stack walker option to configure the stack frame information obtained by a StackWalker.
abstract	StackFrame A StackFrame object represents a method invocation returned by StackWalker.

Public methods
Unit	forEach(action: Consumer<in StackWalker.StackFrame!>!) Performs the given action on each element of StackFrame stream of the current thread, traversing from the top frame of the stack, which is the method calling this forEach method.
Class<*>!	getCallerClass() Gets the Class object of the caller who invoked the method that invoked getCallerClass.
static StackWalker!	getInstance() Returns a StackWalker instance.
static StackWalker!	getInstance(option: StackWalker.Option!) Returns a StackWalker instance with the given option specifying the stack frame information it can access.
static StackWalker!	getInstance(options: MutableSet<StackWalker.Option!>!) Returns a StackWalker instance with the given options specifying the stack frame information it can access.
static StackWalker!	getInstance(options: MutableSet<StackWalker.Option!>!, estimateDepth: Int) Returns a StackWalker instance with the given options specifying the stack frame information it can access.
T	walk(function: Function<in Stream<StackWalker.StackFrame!>!, out T>!) Applies the given function to the stream of StackFrames for the current thread, traversing from the top frame of the stack, which is the method calling this walk method.

Public methods

forEach

Added in API level 34

fun forEach(action: Consumer<in StackWalker.StackFrame!>!): Unit

Performs the given action on each element of StackFrame stream of the current thread, traversing from the top frame of the stack, which is the method calling this forEach method.

This method is equivalent to calling

walk(s -> { s.forEach(action); return null; });

Parameters
action	Consumer<in StackWalker.StackFrame!>!: an action to be performed on each StackFrame of the stack of the current thread

getCallerClass

Added in API level 34

fun getCallerClass(): Class<*>!

Gets the Class object of the caller who invoked the method that invoked getCallerClass.

This method filters frames, java.lang.invoke.MethodHandle, and hidden frames regardless of the SHOW_REFLECT_FRAMES and SHOW_HIDDEN_FRAMES options this StackWalker has been configured with.

This method should be called when a caller frame is present. If it is called from the bottom most frame on the stack, IllegalCallerException will be thrown.

This method throws UnsupportedOperationException if this StackWalker is not configured with the RETAIN_CLASS_REFERENCE option.

Return
Class<*>!	Class object of the caller's caller invoking this method.

Exceptions
java.lang.UnsupportedOperationException	if this StackWalker is not configured with Option.RETAIN_CLASS_REFERENCE.
java.lang.IllegalCallerException	if there is no caller frame, i.e. when this getCallerClass method is called from a method which is the last frame on the stack.

getInstance

Added in API level 34

static fun getInstance(): StackWalker!

Returns a StackWalker instance.

This StackWalker is configured to skip all hidden frames and no class reference is retained.

Return
StackWalker!	a StackWalker configured to skip all hidden frames and no class reference is retained.

getInstance

Added in API level 34

static fun getInstance(option: StackWalker.Option!): StackWalker!

Returns a StackWalker instance with the given option specifying the stack frame information it can access.

If a security manager is present and the given option is Option.RETAIN_CLASS_REFERENCE, it calls its java.lang.SecurityManager#checkPermission method for RuntimePermission("getStackWalkerWithClassReference").

Parameters
option	StackWalker.Option!: stack walking option

Return
StackWalker!	a StackWalker configured with the given option

Exceptions
java.lang.SecurityException	if a security manager exists and its checkPermission method denies access.

getInstance

Added in API level 34

static fun getInstance(options: MutableSet<StackWalker.Option!>!): StackWalker!

Returns a StackWalker instance with the given options specifying the stack frame information it can access. If the given options is empty, this StackWalker is configured to skip all hidden frames and no class reference is retained.

If a security manager is present and the given options contains Option.RETAIN_CLASS_REFERENCE, it calls its java.lang.SecurityManager#checkPermission method for RuntimePermission("getStackWalkerWithClassReference").

Parameters
options	MutableSet<StackWalker.Option!>!: stack walking option

Return
StackWalker!	a StackWalker configured with the given options

Exceptions
java.lang.SecurityException	if a security manager exists and its checkPermission method denies access.

getInstance

Added in API level 34

static fun getInstance(
    options: MutableSet<StackWalker.Option!>!, 
    estimateDepth: Int
): StackWalker!

Returns a StackWalker instance with the given options specifying the stack frame information it can access. If the given options is empty, this StackWalker is configured to skip all hidden frames and no class reference is retained.

If a security manager is present and the given options contains Option.RETAIN_CLASS_REFERENCE, it calls its java.lang.SecurityManager#checkPermission method for RuntimePermission("getStackWalkerWithClassReference").

The estimateDepth specifies the estimate number of stack frames this StackWalker will traverse that the StackWalker could use as a hint for the buffer size.

Parameters
options	MutableSet<StackWalker.Option!>!: stack walking options
estimateDepth	Int: Estimate number of stack frames to be traversed.

Return
StackWalker!	a StackWalker configured with the given options

Exceptions
java.lang.IllegalArgumentException	if estimateDepth <= 0
java.lang.SecurityException	if a security manager exists and its checkPermission method denies access.

walk

Added in API level 34

fun <T : Any!> walk(function: Function<in Stream<StackWalker.StackFrame!>!, out T>!): T

Applies the given function to the stream of StackFrames for the current thread, traversing from the top frame of the stack, which is the method calling this walk method.

The StackFrame stream will be closed when this method returns. When a closed Stream<StackFrame> object is reused, IllegalStateException will be thrown.

Parameters
function	Function<in Stream<StackWalker.StackFrame!>!, out T>!: a function that takes a stream of stack frames and returns a result.
<T>	The type of the result of applying the function to the stream of stack frame.

Return
T	the result of applying the function to the stream of stack frame.