ByteBuddy 有什么方法可以将TypeDescription.Generic 转换成合适的java.lang.reflect.Type 吗？

Question

（ByteBuddy API 的表面积非常大，这就是我问这个问题的原因。）

我知道我可以使用 TypeDescription.Generic 和 determine its "sort" 并从那里“手动”相当费力地进行，但我经常发现某处埋藏着一种方法会为我做这种繁琐的工作。

编辑：一位评论者要求提供“乏味”的食谱。在这里（退后一步；请注意各种 Type 的各种实现或多或少是您所期望的）：

 public static final Type toType(final TypeDefinition type) throws ReflectiveOperationException {
    final Type returnValue;
    if (type == null) {
      returnValue = null;
    } else {
      final TypeDescription.Generic genericType = type.asGenericType();
      switch (type.getSort()) {
      case GENERIC_ARRAY:
        returnValue = new DefaultGenericArrayType(toType(type.getComponentType()));
        break;
      case NON_GENERIC:
        returnValue = Class.forName(type.getTypeName(), false, Thread.currentThread().getContextClassLoader());
        break;
      case PARAMETERIZED:
        final TypeDefinition ownerType = genericType.getOwnerType();
        final TypeDefinition rawType = type.asErasure();
        final List<? extends TypeDefinition> actualTypeArguments = genericType.getTypeArguments();
        if (actualTypeArguments == null || actualTypeArguments.isEmpty()) {
          returnValue = new DefaultParameterizedType(toType(ownerType), toType(rawType));
        } else {
          final Type[] actualJavaTypeArguments = new Type[actualTypeArguments.size()];
          for (int i = 0; i < actualTypeArguments.size(); i++) {
            actualJavaTypeArguments[i] = toType(actualTypeArguments.get(i));
          }
          returnValue = new DefaultParameterizedType(toType(ownerType), toType(rawType), actualJavaTypeArguments);
        }
        break;
      case VARIABLE:
        final TypeVariableSource typeVariableSource = genericType.getTypeVariableSource();
        final GenericDeclaration gd;
        if (typeVariableSource instanceof TypeDefinition typeDefinition) {
          gd = Class.forName(typeDefinition.asErasure().getTypeName(), false, Thread.currentThread().getContextClassLoader());
        } else if (typeVariableSource instanceof MethodDescription.InDefinedShape methodDescription) {
          // Reflection time
          final String name = methodDescription.getName();
          final Class<?> cls = Class.forName(methodDescription.getDeclaringType().asErasure().getTypeName(), false, Thread.currentThread().getContextClassLoader());
          final List<? extends TypeDefinition> parameterTypes = methodDescription.getParameters().asTypeList();
          final Class<?>[] parameterClasses = new Class<?>[parameterTypes.size()];
          for (int i = 0; i < parameterTypes.size(); i++) {
            parameterClasses[i] = Class.forName(parameterTypes.get(i).asErasure().getName(), false, Thread.currentThread().getContextClassLoader());
          }
          if (MethodDescription.CONSTRUCTOR_INTERNAL_NAME.equals(name)) {
            assert TypeDescription.VOID.equals(methodDescription.getReturnType());
            gd = cls.getDeclaredConstructor(parameterClasses);
          } else {
            assert !MethodDescription.TYPE_INITIALIZER_INTERNAL_NAME.equals(name);
            gd = cls.getDeclaredMethod(name, parameterClasses);            
          }
        } else {
          throw new IllegalArgumentException("Unexpected type variable source: " + typeVariableSource);
        }
        final TypeVariable<?>[] typeVariables = gd.getTypeParameters();
        TypeVariable<?> temp = null;
        for (final TypeVariable<?> typeVariable : typeVariables) {
          if (typeVariable.getName().equals(genericType.getSymbol())) {
            temp = typeVariable;
            break;
          }
        }
        assert temp != null;
        returnValue = temp;
        break;
      case VARIABLE_SYMBOLIC:
        throw new IllegalArgumentException("Unexpected type: " + type);
      case WILDCARD:
        final List<? extends TypeDefinition> upperBounds = genericType.getUpperBounds();
        final List<? extends TypeDefinition> lowerBounds = genericType.getLowerBounds();
        if (lowerBounds == null || lowerBounds.isEmpty()) {
          if (upperBounds == null || upperBounds.isEmpty() || (upperBounds.size() == 1 && TypeDescription.Generic.OBJECT.equals(upperBounds.get(0)))) {
            returnValue = UnboundedWildcardType.INSTANCE;
          } else {
            // Upper bounded.
            final Type[] upperJavaBounds = new Type[upperBounds.size()];
            for (int i = 0; i < upperBounds.size(); i++) {
              upperJavaBounds[i] = toType(upperBounds.get(i)); // XXX recursive
            }
            returnValue = new UpperBoundedWildcardType(upperJavaBounds);
          }
        } else {
          assert upperBounds == null || upperBounds.isEmpty() || (upperBounds.size() == 1 && TypeDescription.Generic.OBJECT.equals(upperBounds.get(0))) : "Unexpected upper bounds: " + upperBounds + "; lower bounds: " + lowerBounds;
          // Lower bounded.
          assert lowerBounds.size() == 1 : "Unexpected size in lower bounds: " + lowerBounds;
          returnValue = new LowerBoundedWildcardType(toType(lowerBounds.get(0))); // XXX recursive
        }
        break;        
      default:
        throw new IllegalArgumentException("Unexpected type: " + type);
      }
    }
    return returnValue;
  }

Answer 1

不，您只能将 Type 转换为 TypeDescription.Generic，但没有其他方法可以转换。模拟这个最简单的选择可能是定义一个 class 来定义给定 Type 的字段，加载这个 class 并使用 Java 读取字段类型反射。

Byte Buddy 无法将描述转换为 Type 的原因是 Byte Buddy 抽象出 class 加载器并且类型变量可能与其声明源分离。

ByteBuddy 有什么方法可以将TypeDescription.Generic 转换成合适的java.lang.reflect.Type 吗？

Is there any method in ByteBuddy to convert a TypeDescription.Generic into an appropriate java.lang.reflect.Type?

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