Has this method ever been called inside a running JVM

问题

Is there a way to figure out if a method ever been called inside running JVM. Let's say I have the following method information and I want to know if it has ever been called:

    "methodId": {
      "className": "InvokerParser",
      "filePath": "org/foo/commons/functors/InvokerParserformer.java",
      "methodName": "parser"
    }

回答1:

If the application is running on HotSpot JVM, it is possible to get the information about the given method using HotSpot Serviceability Agent.

Here is a tool that checks whether the method has been called in a running JVM.

import sun.jvm.hotspot.oops.InstanceKlass;
import sun.jvm.hotspot.oops.Method;
import sun.jvm.hotspot.runtime.VM;
import sun.jvm.hotspot.tools.Tool;

public class CheckMethodCall extends Tool {
    private static final String className = "java/util/HashMap";
    private static final String methodName = "get";
    private static final String methodSig = "(Ljava/lang/Object;)Ljava/lang/Object;";

    @Override
    public void run() {
        boolean[] result = new boolean[2];

        VM.getVM().getSystemDictionary().classesDo(klass -> {
            if (klass.getName().asString().equals(className)) {
                Method method = ((InstanceKlass) klass).findMethod(methodName, methodSig);
                if (method != null) {
                    result[0] = true;
                    result[1] = method.getMethodCounters() != null &&
                        method.getInvocationCount() + method.interpreterInvocationCount() > 0;
                }
            }
        });

        if (!result[0]) {
            System.out.println("Method not found");
        } else if (result[1]) {
            System.out.println("Method has been called");
        } else {
            System.out.println("Method has NOT been called");
        }
    }

    public static void main(String[] args) {
        new CheckMethodCall().execute(args);
    }
}

It requires sa-jdi.jar in classpath (comes with JDK 8).

Run

java -cp $JAVA_HOME/lib/sa-jdi.jar:. CheckMethodCall <pid>

where <pid> is Java process ID to check.

UPDATE

A similar tool for JDK 11+
Use --add-modules=jdk.hotspot.agent and export all the required packages.

import sun.jvm.hotspot.oops.InstanceKlass;
import sun.jvm.hotspot.oops.Klass;
import sun.jvm.hotspot.oops.Method;
import sun.jvm.hotspot.runtime.VM;
import sun.jvm.hotspot.tools.Tool;

public class CheckMethodCall extends Tool {
    private static final String className = "java/util/HashMap";
    private static final String methodName = "get";
    private static final String methodSig = "(Ljava/lang/Object;)Ljava/lang/Object;";

    @Override
    public void run() {
        Klass klass = VM.getVM().getClassLoaderDataGraph().find(className);
        if (klass == null) {
            System.out.println("Class not found");
            return;
        }

        Method method = ((InstanceKlass) klass).findMethod(methodName, methodSig);
        if (method == null) {
            System.out.println("Method not found");
            return;
        }

        boolean called = method.getMethodCounters() != null &&
                method.getInvocationCount() + method.interpreterInvocationCount() > 0;
        System.out.println("Method " + (called ? "has been" : "has NOT been") + " called");
    }

    public static void main(String[] args) {
        new CheckMethodCall().execute(args);
    }
}

来源：https://stackoverflow.com/questions/55698109/has-this-method-ever-been-called-inside-a-running-jvm

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