- theory: https://github.com/mtumilowicz/java-stack
- comparison to java 8: https://github.com/mtumilowicz/java8-stack-stackwalking
- java 9 introduced a new API for stack-walking
- API is represented by single
StackWalkerclass - easy and efficient - evaluates the stack frames lazily (stream based)
- method to get the reference of the caller's class
- is thread-safe
- enum
- configures StackWalker
- values
RETAIN_CLASS_REFERENCE-StackFramewill contain reference to theClassobject of the method represented by this frameSHOW_HIDDEN_FRAMES- show all hidden frames (for example - implementation specific and reflection frames are not included by default)SHOW_REFLECT_FRAMES- show only reflection frames ( specific implementation frames could still be hidden)
- note that there is also enum
StackWalker.ExtendedOptionwith only one, self-explaining valueLOCALS_AND_OPERANDS
- interface
- we don't have direct access to concrete implementation
- useful methods:
String getClassName()String getMethodName()int getLineNumber()public Class<?> getDeclaringClass()UnsupportedOperationExceptionif not configured withRETAIN_CLASS_REFERENCE
- creating instance of
StackWalkerstatic StackWalker getInstance()static StackWalker getInstance(Option option)static StackWalker getInstance(Set<Option> options)static StackWalker getInstance(Set<Option> options, int estimateDepth)estimateDepthspecifies the estimate number of stack frames thisStackWalkerwill traverse that theStackWalkercould use as a hint for the buffer size
- traverse the stack
void forEach(Consumer<? super StackFrame> action)- traversing from the top frame of the stack, which is the method calling this
forEachmethod
- traversing from the top frame of the stack, which is the method calling this
<T> T walk(Function<? super Stream<StackFrame>, ? extends T> function)- returning a Stream would be unsafe, as the stream could be used to access the stack frames in an uncontrolled manner
- applies the given function to the stream of
StackFramesfor the current thread, traversing from the top frame of the stack - stream will be closed when this method returns
- the Java virtual machine is free to reorganize a thread's control stack, for example, via
deoptimization - by taking a
Functionparameter, this method allows access to stack frames through a stable view of a thread's control stack
- for test purposes
class StackWalking { void m1() { m2(); } private void m2() { m3(); } private void m3() { System.out.println("---"); System.out.println("stack from m3():"); StackWalker.getInstance(Set.of(RETAIN_CLASS_REFERENCE, SHOW_HIDDEN_FRAMES), 4) .walk(frames -> { frames.limit(4).forEach(System.out::println); return null; }); System.out.println("---"); m4(); } private void m4() { System.out.println("---"); System.out.println("stack from m4():"); StackWalker.getInstance(Set.of(RETAIN_CLASS_REFERENCE, SHOW_HIDDEN_FRAMES), 5) .walk(frames -> { frames.limit(5).forEach(System.out::println); return null; }); System.out.println("---"); } } - simulation
produces
@Test public void simulation() { new StackWalking().m1(); }--- stack from m3(): StackWalking.m3(StackWalking.java:22) StackWalking.m2(StackWalking.java:15) StackWalking.m1(StackWalking.java:11) StackWalkingTest.simulation(StackWalkingTest.java:10) --- --- stack from m4(): StackWalking.m4(StackWalking.java:35) StackWalking.m3(StackWalking.java:28) StackWalking.m2(StackWalking.java:15) StackWalking.m1(StackWalking.java:11) StackWalkingTest.simulation(StackWalkingTest.java:10) ---