使用Byte Buddy拦截默认构造函数

Question

我试图用Byte Buddy拦截构造函数调用,这是我的示例代码:

package t;

import static net.bytebuddy.dynamic.loading.ClassLoadingStrategy.Default.INJECTION;
import static net.bytebuddy.implementation.MethodDelegation.to;
import static net.bytebuddy.matcher.ElementMatchers.any;
import java.util.concurrent.Callable;
import net.bytebuddy.ByteBuddy;
import net.bytebuddy.implementation.bind.annotation.RuntimeType;
import net.bytebuddy.implementation.bind.annotation.SuperCall;

public class Bar {
  public static void main (String[] args) {
    new ByteBuddy ().subclass (Object.class)
      .name ("t.Foo").constructor (any ()).intercept (to (new Object () {

        @RuntimeType
        public Object construct (@SuperCall Callable<Object> z) throws Exception {
          System.out.println ("CALLING XTOR");
          return z.call ();
        }
      })).make ().load (Bar.class.getClassLoader (), INJECTION).getLoaded ();
  }
}

产生以下异常:

Exception in thread "main" java.lang.IllegalStateException: Error invoking java.lang.ClassLoader#findClass
  at net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection$Dispatcher$Resolved.loadClass(ClassInjector.java:392)
  at net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection.inject(ClassInjector.java:201)
  at net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default$InjectionDispatcher.load(ClassLoadingStrategy.java:199)
  at net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default.load(ClassLoadingStrategy.java:114)
  at net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:3302)
  at t.Bar.main(Bar.java:21)
Caused by: java.lang.ClassFormatError: Bad method name at constant pool index 19 in class file t/Foo$auxiliary$EalKkAhD
  at java.lang.ClassLoader.defineClass1(Native Method)
  at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:497)
  at net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection$Dispatcher$Resolved.loadClass(ClassInjector.java:388)
  ... 5 more

我看到了这个相关的问题但我得到了一个碰撞异常(好像构造函数被定义了两次).

Answer 1

您无法为构造函数的超级方法调用创建处理程序.JVM的验证程序确保任何构造函数只调用一次另一个构造函数.必须将此调用硬编码到调用构造函数的方法中.

请注意,此限制适用于任何Java字节代码,甚至适用于处理MethodHandles的情况.构造函数是一个很大的例外.

要使您的示例工作,您需要在委派之前或之后调用超级构造函数.请注意,如果在调用另一个构造函数之前this拦截,则无法访问拦截器定义的任何属性(例如,通过@This或通过@SuperCall,可以读取参数).

对于您的代码示例,只需将拦截器链接起来SuperCall,使调用变为硬编码,如以下示例代码所示:

new ByteBuddy().subclass(Object.class)
               .name("t.Foo")
               .constructor(any()).intercept(to(new Object() {
                 public void construct() throws Exception {
                   System.out.println("CALLING XTOR");
                 }
               }).andThen(SuperMethodCall.INSTANCE)) // This makes the difference!
               .make()
               .load(Bar.class.getClassLoader(), INJECTION)
               .getLoaded()

我同意Byte Buddy应该对这个问题提供更多信息.我将为此场景添加适当的运行时处理(即该方法不再考虑绑定).