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java - 返回子类型时是否需要 Assigner.Typing.DYNAMIC 分配器？

问题描述

假设我希望Function<Object, Object>通过做一些非常愚蠢的事情来实现接口：

final ParameterizedType whatTheUserWillSee = functionObjectObject(); // e.g. Function<Object, Object>
DynamicType.Builder<?> builder = builder
  .subclass(Object.class, ConstructorStrategy.Default.NO_CONSTRUCTORS)
      .merge(Visibility.PUBLIC, SyntheticState.SYNTHETIC, TypeManifestation.FINAL)
      .defineConstructor(Visibility.PUBLIC, SyntheticState.SYNTHETIC)
      .intercept(MethodCall.invoke(OBJECT_CONSTRUCTOR).onSuper()) // OBJECT_CONSTRUCTOR is just new Object()
      .implement(whatTheUserWillSee)
      .intercept(MethodCall.invoke(new MethodDescription.ForLoadedMethod(Object.class.getMethod("toString"))
                 .withAssigner(Assigner.DEFAULT, Assigner.Typing.DYNAMIC));

也就是说，我正在创建这样的东西：

public Foo() {
  super();
}
public Object apply(Object x) {
  return toString();
}

没有.withAssigner调用，我得到：

java.lang.IllegalStateException: Cannot return class java.lang.String from public java.util.function.Function java.util.function.Function.compose(java.util.function.Function)
    at net.bytebuddy.implementation.MethodCall$TerminationHandler$Simple$1.toStackManipulation(MethodCall.java:3005)
    at net.bytebuddy.implementation.MethodCall$Appender.toStackManipulation(MethodCall.java:3551)
    at net.bytebuddy.implementation.MethodCall$Appender.apply(MethodCall.java:3509)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyCode(TypeWriter.java:708)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod$WithBody.applyBody(TypeWriter.java:693)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$MethodPool$Record$ForDefinedMethod.apply(TypeWriter.java:600)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default$ForCreation.create(TypeWriter.java:5660)
    at net.bytebuddy.dynamic.scaffold.TypeWriter$Default.make(TypeWriter.java:2166)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:232)
    at net.bytebuddy.dynamic.scaffold.subclass.SubclassDynamicTypeBuilder.make(SubclassDynamicTypeBuilder.java:204)
    at net.bytebuddy.dynamic.DynamicType$Builder$AbstractBase.make(DynamicType.java:3595)

我不是 ByteBuddy 内部的专家。为什么需要动态类型分配器才能返回 的子类型Object？

标签： javabyte-buddy

解决方案

您正在拦截Function. 当你认为你在拦截apply时，如果你仔细看，Byte Buddy是在抱怨这个compose方法。指定一个显式匹配器来避免这种情况。

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