Java反射:如何从一个对象中获取字段值，而不知道它的类 [英] Java reflection: how to get field value from an object, not knowing its class

问题描述

比如说，我有一个方法可以返回一个带有一些对象的自定义 List.它们作为 Object 返回给我.我需要从这些对象中获取某个字段的值，但我不知道这些对象的类.

Say, I have a method that returns a custom List with some objects. They are returned as Object to me. I need to get value of a certain field from these objects, but I don't know the objects' class.

有没有办法通过 Reflecion 或其他方式做到这一点?

Is there a way to do this via Reflecion or somehow else?

推荐答案

假设一个简单的案例，你的字段是 public:

Assuming a simple case, where your field is public:

List list; // from your method
for(Object x : list) {
    Class<?> clazz = x.getClass();
    Field field = clazz.getField("fieldName"); //Note, this can throw an exception if the field doesn't exist.
    Object fieldValue = field.get(x);
}

但这很丑陋，我忽略了所有的尝试，并做了一些假设(公共领域、反射可用、优秀的安全管理器).

But this is pretty ugly, and I left out all of the try-catches, and makes a number of assumptions (public field, reflection available, nice security manager).

如果你可以改变你的方法来返回一个List，这就变得很容易了，因为迭代器可以给你类型信息:

If you can change your method to return a List<Foo>, this becomes very easy because the iterator then can give you type information:

List<Foo> list; //From your method
for(Foo foo:list) {
    Object fieldValue = foo.fieldName;
}

或者，如果您使用的是 Java 1.4 接口，其中泛型不可用，但您知道应该在列表中的对象的类型...

Or if you're consuming a Java 1.4 interface where generics aren't available, but you know the type of the objects that should be in the list...

List list;
for(Object x: list) {
   if( x instanceof Foo) {
      Object fieldValue = ((Foo)x).fieldName;
   }
}

不需要反射:)

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