java在运行时获取泛型类型

java在运行时获取泛型类型

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获取泛型

interface Foo<T1, T2> {}
class Bar implements Foo<Integer, String> {}

Class<?>[] typeArgs = TypeResolver.resolveRawArguments(Foo.class, Bar.class);

assert typeArgs[0] == Integer.class;
assert typeArgs[1] == String.class;

获取lambda的泛型

Function<String, Integer> strToInt = s -> Integer.valueOf(s);
Class<?>[] typeArgs = TypeResolver.resolveRawArguments(Function.class, strToInt.getClass());

assert typeArgs[0] == String.class;
assert typeArgs[1] == Integer.class;

//-----------------------

Comparator<String> comparator = String::compareToIgnoreCase;
Class<?> typeArg = TypeResolver.resolveRawArgument(Comparator.class, comparator.getClass());

assert typeArg == String.class;

获取组合List的泛型

interface Foo<T> {}
class Bar implements Foo<List<Integer>> {}

Type typeArgs = TypeResolver.reify(Foo.class, Bar.class);

ParameterizedType paramType = (ParameterizedType) typeArgs;
Type[] actualTypeArgs = paramType.getActualTypeArguments();
ParameterizedType arg = (ParameterizedType)actualTypeArgs[0];

assert paramType.getRawType() == Foo.class;
assert arg1.getRawType() == List.class;
assert arg1.getActualTypeArguments()[0] == Integer.class;

获取成员变量的泛型

class Entity<ID extends Serializable> {
  ID id;
  void setId(ID id) {}
}

class SomeEntity extends Entity<Long> {}

Type fieldType = Entity.class.getDeclaredField("id").getGenericType();
Type mutatorType = Entity.class.getDeclaredMethod("setId", Serializable.class).getGenericParameterTypes()[0];

assert TypeResolver.resolveRawClass(fieldType, SomeEntity.class) == Long.class;
assert TypeResolver.resolveRawClass(mutatorType, SomeEntity.class) == Long.class;