使用Byte-Buddy拦截java.lang.Object wait（long）本机方法

Question

我正在尝试记录“object.wait”方法调用的计数。截取“public final native void wait（long timeout）”对ByteBuddy无效。我做了一些测试：

test1,test2打印错误：java.lang.IllegalStateException：无法为公共最终void java.lang.Object.Wait（long,int）调用超级（或默认）方法抛出java.lang.InterruptedException；java.lang.IllegalStateException：无法为公共最终本机void java.lang.Object.Wait（长）抛出java.lang.InterruptedException调用超级（或默认）方法

test3无效，不打印任何内容。

测试4为成功。

下面是我的测试代码：

final public class AgentBootstrap {

     public static class TestAdvice {
        @Advice.OnMethodEnter
        public static void before(@Advice.Origin String methodIns) {
            System.out.println("Byte-Buddy enter:" + methodIns);
        }

        @Advice.OnMethodExit
        public static void after(@Advice.Origin String methodIns) {
            System.out.println("Byte-Buddy after:" + methodIns);
        }
      }
    
     public static void premain(String agentArgs, Instrumentation inst) throws Exception{
         AgentBuilder agentBuilder = new AgentBuilder.Default()
                .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
                .with(AgentBuilder.InitializationStrategy.NoOp.INSTANCE)
                .with(AgentBuilder.TypeStrategy.Default.REBASE)
                .enableNativeMethodPrefix("$$mynative_")
                .with(AgentBuilder.Listener.StreamWriting.toSystemError().withErrorsOnly())
                .with(AgentBuilder.InstallationListener.StreamWriting.toSystemError())
                .ignore(nameStartsWith("net.bytebuddy."));
        // test1(agentBuilder, inst);
        // test2(agentBuilder, inst);
        // test3(agentBuilder, inst);
        // test4(agentBuilder, inst);
        
    }
     
    /**
     * intercept method: public final native void wait(long timeout)
     * print error: java.lang.IllegalStateException: Cannot call super (or default) method for public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException
     */
    private static void test1(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
        agentBuilder.disableClassFormatChanges()
        .type(is(Object.class))
        .transform(new Transformer() {
            @Override
            public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
              return builder.method(named("wait").and(takesArguments(1))).intercept(Advice.to(TestAdvice.class));
            }
        })
        .installOn(inst);
        inst.retransformClasses(Object.class);
    }
    /**
     * intercept method: public final void wait(long timeout, int nanos)
     * print error: java.lang.IllegalStateException: Cannot call super (or default) method for public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException
     */
    private static void test2(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
        agentBuilder.disableClassFormatChanges()
        .type(is(Object.class))
        .transform(new Transformer() {
            @Override
            public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
              return builder.method(named("wait").and(takesArguments(2))).intercept(Advice.to(TestAdvice.class));
            }
        })
        .installOn(inst);
        inst.retransformClasses(Object.class);
    }
    
    /**
     * intercept method: public final native void wait(long timeout)
     * invalid, print nothing
     */
    private static void test3(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
        agentBuilder.disableClassFormatChanges()
        .type(is(Object.class))
        .transform(new Transformer() {
            @Override
            public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
                return builder.visit(Advice.to(TestAdvice.class).on(named("wait").and(takesArguments(1))));
            }
        })
        .installOn(inst);
        inst.retransformClasses(Object.class);
    }
    /**
     * intercept method: public final void wait(long timeout, int nanos)
     * success
     */
    private static void test4(AgentBuilder agentBuilder, Instrumentation inst) throws Exception {
        agentBuilder.type(is(Object.class))
        .transform(new Transformer() {
            @Override
            public Builder<?> transform(Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader,JavaModule module) {
                return builder.visit(Advice.to(TestAdvice.class).on(named("wait").and(takesArguments(2))));
            }
        })
        .installOn(inst);
    }
     
}

public static void main(String[] args) throws Exception {
    new Thread(() -> {
        Object obj = new Object();
        while (true){
            try {
                synchronized (obj) {
                    obj.wait(1000);
                    obj.wait(1000, 1);
                }
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
    }).start();
}

：(Test4代码是针对“public final void wait（）”方法的，它起作用了，但是对于“public final native void wait（）”方法却不起作用。我想知道如何拦截“public final native void wait（）”方法。

Answer 1

研究一下这个问题，实际上Byte Buddy版本1.10.14中存在一个bug。重新基于的方法必须具有修饰符private final而不是仅仅private，否则，JVM将不接受重新基于的方法。

修复程序已经在master上了，如果您自己构建了Byte Buddy，您现在应该可以运行代理了。下一个版本1.10.15将包含此修补程序。

但是，请注意，JVM不再支持从版本13开始添加私有（final）方法。可以使用-xx:+AllowRedefinitionToAddDeleteMethods重置旧的行为。但是，该选项不推荐使用，并且在JVM的未来版本中将不再存在。如果没有这种重命名本机方法的可能性，那么在JVM上，无论有没有Byte buddy，这种行为都是不可能的。

（透露一下，我是Byte Buddy的维护者。）