java 如何使用java反射获取类型参数值？
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How to get type parameter values using java reflection?
提问by mik01aj
interface Foo<T> { ... }
class Bar implements Foo<Baz> { ... }
I've got a Barobject. How to get the value of Tfor it (Baz)?
我有Bar对象 如何获得它的值T( Baz)？
So far, I only managed to get the interface and T, but I can't see a way to get its value.
到目前为止，我只设法获得了接口 and T，但我看不到获得其价值的方法。
Thanks in advance.
提前致谢。
回答by Bozho
Type type = bar.getClass().getGenericInterfaces()[0];
if (type instanceof ParameterizedType) {
Type actualType = ((ParameterizedType) type).getActualTypeArguments()[0];
System.out.println(actualType);
}
Of course, in the general case, you should iterate over the array, rather than assuming it has excatly one element ([0]). With the above example, you can cast actualTypeto java.lang.Class. In other cases it may be different (see comment by meriton)
当然，在一般情况下，您应该遍历数组，而不是假设它只有一个元素 ( [0])。使用上面的示例，您可以强制转换actualType为java.lang.Class. 在其他情况下可能会有所不同（请参阅meriton的评论）
回答by Dan Godfrey
If you already have Guava on the classpath, this is a bit more robust as you specify the interface/superclass by type rather than index.
如果您已经在类路径上安装了 Guava，那么当您按类型而不是索引指定接口/超类时，这会更健壮一些。
TypeToken<?> baz = TypeToken.of(Bar.class).resolveType(Foo.class.getTypeParameters()[0]);
System.out.println(baz.getRawType()); // class Baz
