java - 如何通过检查找到返回类型的参数化类型？

Question

我正在使用反射来获取类中的所有方法，如下所示:

Method[] allMethods = c.getDeclaredMethods();

之后我将迭代这些方法

for (Method m: allMethods){
    //I want to find out if the return is is a parameterized type or not
    m.getReturnType();
}

例如:如果我有这样的方法:

public Set<Cat> getCats();

如何使用反射来找出包含 Cat 作为参数化类型的返回类型？

Answer 1

你试过吗getGenericReturnType() ？

Returns a Type object that represents the formal return type of the method represented by this Method object.

If the return type is a parameterized type, the Type object returned must accurately reflect the actual type parameters used in the source code.

If the return type is a type variable or a parameterized type, it is created. Otherwise, it is resolved.

然后(从Javadocs来看)，似乎你必须将其转换为 ParameterizedType并调用getActualTypeArguments()就在上面。

这里是一些示例代码:

    for (Method m : allMethods) {
        Type t = m.getGenericReturnType();
        if (t instanceof ParameterizedType) {
            System.out.println(t);       // "java.util.Set<yourpackage.Cat>"
            for (Type arg : ((ParameterizedType)t).getActualTypeArguments()) {
                System.out.println(arg); // "class yourpackage.Cat"
            }
        }
    }