如何使用 ByteBuddy 代理处理构造函数抛出的异常？

Question

我正在尝试使用ByteBuddy (v1.7.9) java 代理记录在方法和构造函数中抛出的每个调用、返回的对象和异常，而不干扰检测代码的正常功能。

我当前的代理实例是

new AgentBuilder.Default()
                .with(AgentBuilder.Listener.StreamWriting.toSystemOut())
                .type((typeDescription, classLoader, module, classBeingRedefined, protectionDomain) -> 
                     matcher.matchesIncoming(typeDescription.getTypeName()))
                .transform((builder, typeDescription, classLoader, javaModule) -> builder
                        .visit(Advice.to(CustomAdvicer.class).on(ElementMatchers.any())))
                .installOn(inst);

我从最简单的“顾问”开始，

public class CustomAdvicer {
    @Advice.OnMethodEnter
    public static void enter(@Advice.Origin String origin) {
        System.out.println("Entering " + origin);
    }

    @Advice.OnMethodExit(onThrowable = Throwable.class)
    public static void exit(
        @Advice.Return(typing = Assigner.Typing.DYNAMIC) @RuntimeType Object value,
        @Advice.Origin String origin,
        @Advice.Thrown Throwable thrown) {
        System.out.println("Exiting " + origin);
    }
}

但是，当我运行该程序时，我从 bytebuddy 收到一个异常：

[Byte Buddy] ERROR some.pack.Thrower [sun.misc.Launcher$AppClassLoader@18b4aac2, null, loaded=false]
java.lang.IllegalStateException: Cannot catch exception during constructor call for public some.pack.Thrower() throws java.lang.Exception
    at net.bytebuddy.asm.Advice.doWrap(Advice.java:515)
    at net.bytebuddy.asm.Advice.wrap(Advice.java:470)
    at net.bytebuddy.asm.AsmVisitorWrapper$ForDeclaredMethods$Entry.wrap(AsmVisitorWrapper.java:481)
    at net.bytebuddy.asm.AsmVisitorWrapper$ForDeclaredMethods$DispatchingVisitor.visitMethod(AsmVisitorWrapper.java:562)
    at net.bytebuddy.jar.asm.ClassVisitor.visitMethod(ClassVisitor.java:327)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForInlining$RedefinitionClassVisitor.visitMethod(TypeWriter.java:3801)
    at net.bytebuddy.jar.asm.ClassReader.readMethod(ClassReader.java:1020)
    at net.bytebuddy.jar.asm.ClassReader.accept(ClassReader.java:698)
    at net.bytebuddy.jar.asm.ClassReader.accept(ClassReader.java:500)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForInlining.create(TypeWriter.java:2941)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:1633)
    at net.bytebuddy.dynamic.scaffold.inline.RebaseDynamicTypeBuilder.make(RebaseDynamicTypeBuilder.java:200)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$Transformation$Simple$Resolution.apply(AgentBuilder.java:8905)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:9306)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:9269)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1300(AgentBuilder.java:9047)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:9625)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$LegacyVmDispatcher.run(AgentBuilder.java:9575)
    at java.security.AccessController.doPrivileged(Native Method)
    at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:9194)
    at sun.instrument.TransformerManager.transform(Unknown Source)
    at sun.instrument.InstrumentationImpl.transform(Unknown Source)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at Main.main(Main.java:23)

那么，我应该怎么做才能记录在 constructors 中抛出的异常，记住它不能干扰原始代码？

顺便说一下，Thrower 类是我写的一个愚蠢的类来测试这个案例：

package some.pack;

public class Thrower {
  public Thrower() throws Exception {
    throw new Exception("By courtesy of thrower! ;)");
  }
}

Answer 1

问题是构造函数有一个隐式的第一条指令，它是另一个或超级构造函数的调用。 你的Thrower类实际上是这样的：

public class Thrower {
  public Thrower() throws Exception {
    super();
    throw new Exception("By courtesy of thrower! ;)");
  }
}

如果您想将整个调用包装在 try-catch 块中，这将产生以下结果：

public class Thrower {
  public Thrower() throws Exception {
    try {
      super();
      throw new Exception("By courtesy of thrower! ;)");
    } catch (Exception e) {
      ...
    }
  }
}

但这在 JVM 中是不合法的，因此 Byte Buddy 不允许这样做。 没有一种好方法可以排除超级构造函数调用，因为这是第一次调用只是 Java 语言约定，但字节码允许更多任意组合。 由于您无法知道一个类来自哪种语言，因此 Byte Buddy 不会在这里尝试任何技巧，只是不允许这样做。