Java反射 - 访问受保护的字段 [英] Java reflection - access protected field

问题描述

如何通过反射从对象访问继承的受保护字段？

How can I access an inherited protected field from an object by reflection?

推荐答案

您可能遇到的两个问题 - 该字段可能无法正常访问（私有），并且它不在您正在查看的类中，而是在层次结构中的某个位置。

Two issues you may be having issues with - the field might not be accessible normally (private), and it's not in the class you are looking at, but somewhere up the hierarchy.

这样的东西甚至可以工作有这些问题：

Something like this would work even with those issues:

public class SomeExample {

  public static void main(String[] args) throws Exception{
    Object myObj = new SomeDerivedClass(1234);
    Class myClass = myObj.getClass();
    Field myField = getField(myClass, "value");
    myField.setAccessible(true); //required if field is not normally accessible
    System.out.println("value: " + myField.get(myObj));
  }

  private static Field getField(Class clazz, String fieldName)
        throws NoSuchFieldException {
    try {
      return clazz.getDeclaredField(fieldName);
    } catch (NoSuchFieldException e) {
      Class superClass = clazz.getSuperclass();
      if (superClass == null) {
        throw e;
      } else {
        return getField(superClass, fieldName);
      }
    }
  }
}

class SomeBaseClass {
  private Integer value;

  SomeBaseClass(Integer value) {
    this.value = value;
  }
}

class SomeDerivedClass extends SomeBaseClass {
  SomeDerivedClass(Integer value) {
    super(value);
  }
}

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