Class StackWalker
- java.lang.Object
-
- java.lang.StackWalker
public final class StackWalker extends Object
A stack walker.
The walk
method opens a sequential stream of StackFrame
s 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 StackFrame
s 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.
- API Note:
- Examples
1. To find the first caller filtering a known list of implementation class:
StackWalker walker = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE); Optional<Class<?>> callerClass = walker.walk(s -> s.map(StackFrame::getDeclaringClass) .filter(interestingClasses::contains) .findFirst());
2. To snapshot the top 10 stack frames of the current thread,
List<StackFrame> stack = StackWalker.getInstance().walk(s -> s.limit(10).collect(Collectors.toList()));
Unless otherwise noted, passing anull
argument to a constructor or method in thisStackWalker
class will cause aNullPointerException
to be thrown. - Since:
- 9
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
static class | StackWalker.Option | Stack walker option to configure the stack frame information obtained by a |
static interface | StackWalker.StackFrame | A |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | forEach(Consumer<? super StackWalker.StackFrame> action) | Performs the given action on each element of |
Class<?> | getCallerClass() | Gets the |
static StackWalker | getInstance() | Returns a |
static StackWalker | getInstance(StackWalker.Option option) | Returns a |
static StackWalker | getInstance(Set<StackWalker.Option> options) | Returns a |
static StackWalker | getInstance(Set<StackWalker.Option> options,
int estimateDepth) | Returns a |
<T> T | walk(Function<? super Stream<StackWalker.StackFrame>,? extends T> function) | Applies the given function to the stream of |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Method Detail
getInstance
public static StackWalker getInstance()
Returns a StackWalker
instance.
This StackWalker
is configured to skip all hidden frames and no class reference is retained.
- Returns:
- a
StackWalker
configured to skip all hidden frames and no class reference is retained.
getInstance
public static StackWalker getInstance(StackWalker.Option option)
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 checkPermission
method for RuntimePermission("getStackWalkerWithClassReference")
.
- Parameters:
-
option
-stack walking option
- Returns:
- a
StackWalker
configured with the given option - Throws:
-
SecurityException
- if a security manager exists and itscheckPermission
method denies access.
getInstance
public static StackWalker getInstance(Set<StackWalker.Option> options)
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 checkPermission
method for RuntimePermission("getStackWalkerWithClassReference")
.
- Parameters:
-
options
-stack walking option
- Returns:
- a
StackWalker
configured with the given options - Throws:
-
SecurityException
- if a security manager exists and itscheckPermission
method denies access.
getInstance
public static StackWalker getInstance(Set<StackWalker.Option> options, int estimateDepth)
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 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
-stack walking options
-
estimateDepth
- Estimate number of stack frames to be traversed. - Returns:
- a
StackWalker
configured with the given options - Throws:
-
IllegalArgumentException
- ifestimateDepth <= 0
-
SecurityException
- if a security manager exists and itscheckPermission
method denies access.
walk
public <T> T walk(Function<? super Stream<StackWalker.StackFrame>,? extends T> function)
Applies the given function to the stream of StackFrame
s 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.
- API Note:
- For example, to find the first 10 calling frames, first skipping those frames whose declaring class is in package
com.foo
:List<StackFrame> frames = StackWalker.getInstance().walk(s -> s.dropWhile(f -> f.getClassName().startsWith("com.foo.")) .limit(10) .collect(Collectors.toList()));
This method takes a
Function
accepting aStream<StackFrame>
, rather than returning aStream<StackFrame>
and allowing the caller to directly manipulate the stream. The Java virtual machine is free to reorganize a thread's control stack, for example, via deoptimization. By taking aFunction
parameter, this method allows access to stack frames through a stable view of a thread's control stack.Parallel execution is effectively disabled and stream pipeline execution will only occur on the current thread.
- Implementation Note:
- The implementation stabilizes the stack by anchoring a frame specific to the stack walking and ensures that the stack walking is performed above the anchored frame. When the stream object is closed or being reused,
IllegalStateException
will be thrown. - Type Parameters:
-
T
- The type of the result of applying the function to the stream of stack frame. - Parameters:
-
function
- a function that takes a stream of stack frames and returns a result. - Returns:
- the result of applying the function to the stream of stack frame.
forEach
public void forEach(Consumer<? super StackWalker.StackFrame> action)
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
- an action to be performed on eachStackFrame
of the stack of the current thread
getCallerClass
public Class<?> getCallerClass()
Gets the Class
object of the caller who invoked the method that invoked getCallerClass
.
This method filters reflection frames, 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.
- API Note:
- For example,
Util::getResourceBundle
loads a resource bundle on behalf of the caller. It invokesgetCallerClass
to identify the class whose method calledUtil::getResourceBundle
. Then, it obtains the class loader of that class, and uses the class loader to load the resource bundle. The caller class in this example isMyTool
.class Util { private final StackWalker walker = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE); public ResourceBundle getResourceBundle(String bundleName) { Class<?> caller = walker.getCallerClass(); return ResourceBundle.getBundle(bundleName, Locale.getDefault(), caller.getClassLoader()); } } class MyTool { private final Util util = new Util(); private void init() { ResourceBundle rb = util.getResourceBundle("mybundle"); } }
An equivalent way to find the caller class using thewalk
method is as follows (filtering the reflection frames,MethodHandle
and hidden frames not shown below):Optional<Class<?>> caller = walker.walk(s -> s.map(StackFrame::getDeclaringClass) .skip(2) .findFirst());
When thegetCallerClass
method is called from a method that is the bottom most frame on the stack, for example,static public void main
method launched by thejava
launcher, or a method invoked from a JNI attached thread,IllegalCallerException
is thrown. - Returns:
-
Class
object of the caller's caller invoking this method. - Throws:
-
UnsupportedOperationException
- if thisStackWalker
is not configured withOption.RETAIN_CLASS_REFERENCE
. -
IllegalCallerException
- if there is no caller frame, i.e. when thisgetCallerClass
method is called from a method which is the last frame on the stack.