java9系列(五)Stack-Walking API-白红宇

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本文主要研究下

StackWalker

java9新增这个类的目的是提供一个标准API用于访问当前线程栈，之前只有Throwable::getStackTrace、Thread::getStackTrace以及SecurityManager::getClassContext提供了方法可以获取线程栈。

StackWalker.Option

/Library/Java/JavaVirtualMachines/jdk-9.0.4.jdk/Contents/Home/lib/src.zip!/java.base/java/lang/StackWalker.java

/**     * Stack walker option to configure the {@linkplain StackFrame stack frame}     * information obtained by a {@code StackWalker}.     *     * @since 9     */    public enum Option {        /**         * Retains {@code Class} object in {@code StackFrame}s         * walked by this {@code StackWalker}.         *         *  A {@code StackWalker} configured with this option will support         * {@link StackWalker#getCallerClass()} and         * {@link StackFrame#getDeclaringClass() StackFrame.getDeclaringClass()}.         */        RETAIN_CLASS_REFERENCE,        /**         * Shows all reflection frames.         *         * 
By default, reflection frames are hidden.  A {@code StackWalker}         * configured with this {@code SHOW_REFLECT_FRAMES} option         * will show all reflection frames that         * include {@link java.lang.reflect.Method#invoke} and         * {@link java.lang.reflect.Constructor#newInstance(Object...)}         * and their reflection implementation classes.         *         * 
The {@link #SHOW_HIDDEN_FRAMES} option can also be used to show all         * reflection frames and it will also show other hidden frames that         * are implementation-specific.         *         * @apiNote         * This option includes the stack frames representing the invocation of         * {@code Method} and {@code Constructor}.  Any utility methods that         * are equivalent to calling {@code Method.invoke} or         * {@code Constructor.newInstance} such as {@code Class.newInstance}         * are not filtered or controlled by any stack walking option.         */        SHOW_REFLECT_FRAMES,        /**         * Shows all hidden frames.         *         * 
A Java Virtual Machine implementation may hide implementation         * specific frames in addition to {@linkplain #SHOW_REFLECT_FRAMES         * reflection frames}. A {@code StackWalker} with this {@code SHOW_HIDDEN_FRAMES}         * option will show all hidden frames (including reflection frames).         */        SHOW_HIDDEN_FRAMES;    }复制代码

创建StackWalker的选项，可组合使用

RETAIN_CLASS_REFERENCE，可以使用StackWalker#getCallerClass()，StackFrame#getDeclaringClass()，StackFrame.getDeclaringClass()方法

SHOW_REFLECT_FRAMES，默认反射相关的frames是被隐藏的，使用这个选项可以开启

SHOW_HIDDEN_FRAMES，除了反射相关的frames外jvm还会隐藏其他一些实现相关的frame，使用这个选项可以将所有都输出

实例

使用Thread的getStackTrace

@Test    public void testPrintCurrnentStackTrace(){        StackTraceElement[] stack = Thread.currentThread().getStackTrace();        for (StackTraceElement element : stack){            System.out.println(element);        }    }复制代码

输出

java.base/java.lang.Thread.getStackTrace(Thread.java:1654)test.com.packt.lang.StackWalkingTest.testPrintCurrnentStackTrace(StackWalkingTest.java:20)java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)java.base/java.lang.reflect.Method.invoke(Method.java:564)org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)org.junit.runners.ParentRunner.run(ParentRunner.java:363)org.junit.runner.JUnitCore.run(JUnitCore.java:137)com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)复制代码

SHOW_REFLECT_FRAMES

private void print(StackWalker stackWalker){        stackWalker.forEach(stackFrame -> System.out.printf("%6d| %s -> %s %n",                stackFrame.getLineNumber(),                stackFrame.getClassName(),                stackFrame.getMethodName()));    }    @Test    public void testShowReflectFrames(){        final StackWalker stackWalker =                StackWalker.getInstance(Option.SHOW_REFLECT_FRAMES);        print(stackWalker);    }复制代码

输出

19| test.com.packt.lang.StackWalkingTest -> print     43| test.com.packt.lang.StackWalkingTest -> testShowReflectFrames     -2| jdk.internal.reflect.NativeMethodAccessorImpl -> invoke0     62| jdk.internal.reflect.NativeMethodAccessorImpl -> invoke     43| jdk.internal.reflect.DelegatingMethodAccessorImpl -> invoke    564| java.lang.reflect.Method -> invoke     50| org.junit.runners.model.FrameworkMethod$1 -> runReflectiveCall     12| org.junit.internal.runners.model.ReflectiveCallable -> run     47| org.junit.runners.model.FrameworkMethod -> invokeExplosively     17| org.junit.internal.runners.statements.InvokeMethod -> evaluate    325| org.junit.runners.ParentRunner -> runLeaf     78| org.junit.runners.BlockJUnit4ClassRunner -> runChild     57| org.junit.runners.BlockJUnit4ClassRunner -> runChild    290| org.junit.runners.ParentRunner$3 -> run     71| org.junit.runners.ParentRunner$1 -> schedule    288| org.junit.runners.ParentRunner -> runChildren     58| org.junit.runners.ParentRunner -> access$000    268| org.junit.runners.ParentRunner$2 -> evaluate    363| org.junit.runners.ParentRunner -> run    137| org.junit.runner.JUnitCore -> run     68| com.intellij.junit4.JUnit4IdeaTestRunner -> startRunnerWithArgs     47| com.intellij.rt.execution.junit.IdeaTestRunner$Repeater -> startRunnerWithArgs    242| com.intellij.rt.execution.junit.JUnitStarter -> prepareStreamsAndStart     70| com.intellij.rt.execution.junit.JUnitStarter -> main复制代码

比默认的多输出了jdk.internal.reflect相关frames

输出所有frames

@Test    public void testGetAllFrames(){        List
    
      stack =                StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE).walk((s) -> s.collect(Collectors.toList()));        System.out.println("All frames : \n" + stack.toString());    }复制代码

输出

All frames : [test.com.packt.lang.StackWalkingTest.testGetAll(StackWalkingTest.java:54), org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50), org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12), org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47), org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17), org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325), org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78), org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57), org.junit.runners.ParentRunner$3.run(ParentRunner.java:290), org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71), org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288), org.junit.runners.ParentRunner.access$000(ParentRunner.java:58), org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268), org.junit.runners.ParentRunner.run(ParentRunner.java:363), org.junit.runner.JUnitCore.run(JUnitCore.java:137), com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68), com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47), com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242), com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)]复制代码

过滤指定class

@Test    public void testFilterByClass(){        Optional
    
      filteredResult = StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE).walk((s) ->                s.filter(f -> StackWalkingTest.class.equals(f.getDeclaringClass())).findFirst()        );        System.out.println("filter by class : \n"+filteredResult.toString());    }复制代码

输出

filter by class : Optional[test.com.packt.lang.StackWalkingTest.testFilterByClass(StackWalkingTest.java:62)]复制代码

skip

@Test    public void testSkip(){        List
    
      framesAfterSkip = StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE).walk((s) ->                s.skip(2).collect(Collectors.toList()));        System.out.println("frames after skip : \n"+framesAfterSkip.toString());    }复制代码

输出

frames after skip : [org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12), org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47), org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17), org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325), org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78), org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57), org.junit.runners.ParentRunner$3.run(ParentRunner.java:290), org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71), org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288), org.junit.runners.ParentRunner.access$000(ParentRunner.java:58), org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268), org.junit.runners.ParentRunner.run(ParentRunner.java:363), org.junit.runner.JUnitCore.run(JUnitCore.java:137), com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68), com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47), com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242), com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)]复制代码

这里skip了前两行

小结

java9引进的StackWalker可以更方便地打印当前线程堆栈，并提供了相关filter，skip等方法。

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