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- enum
- configures StackWalker
- values
RETAIN_CLASS_REFERENCE - StackFrame will contain
reference to the Class object 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.ExtendedOption
with only one, self-explaining value LOCALS_AND_OPERANDS
- interface
- we don't have direct access to concrete implementation
- useful methods:
String getClassName()String getMethodName()int getLineNumber()public Class<?> getDeclaringClass()
UnsupportedOperationException if not configured with
RETAIN_CLASS_REFERENCE
- creating instance of
StackWalker
static StackWalker getInstance()static StackWalker getInstance(Option option)static StackWalker getInstance(Set<Option> options)static StackWalker getInstance(Set<Option> options, int estimateDepth)
estimateDepth specifies the estimate number of stack frames
this StackWalker will traverse that the StackWalker could
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
forEach method
<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
StackFrames
for 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
Function parameter, 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
@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)
---
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Overview of StackWalker API in java 9.
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