通过反射获取第一个父项的字段

Question

我试图获得我的对象的第一个父的字段和值。我现在的代码是这样的:

Class<? extends Object> cls = obj.getClass();
Field[] fields = cls.getDeclaredFields();
for ( Field field : fields )
{
    String fieldName = field.getName();
    String fieldValue = field.get(obj);
}

我的类结构类似于:

class A
{
    int x;
}
class B extends A
{
    int y;
}
class C extends B
{
    int z;
}

现在，我传递一个C对象的方法，我想从C和B获得所有字段，但不是从a。有办法做到这一点(使用反射，我不想实现其他方法)?

Answer 1

Luchian，使用getSuperclass()方法获取对class对象的引用，该对象表示所讨论对象的超类类型。在此之后，您将很容易获得字段，就像您在示例中所做的那样。

Answer 2

创建方法

public static void printFieldsFor(Class cls, Object obj) {
  Field[] fields = cls.getDeclaredFields();
  for ( Field field : fields ) {
    String fieldName = field.getName();
    String fieldValue = field.get(obj);
  }
}
printFieldsFor(object.getClass(), obj);
printFieldsFor(object.getClass().getSuperclass(), obj);

或使用循环

for(Class cls = object.getClass(); 
    cls!=null && cls!=A.class; 
    cls = cls.getSuperclass()) {
  for(Field field : cls.getDeclaredFields()) {
     String fieldName = field.getName();
     String fieldValue = field.get(obj);
     // do something with the field.
  }
}

Answer 3

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
 * @author pablo.barbosa (2017-08-15)
 */
public class ReflectionUtil {
    /**
     * Hiding constructor. The methods are statics
     */
    private ReflectionUtil() {
        // Hiding constructor
    }
    public static List<Field> getInheritedDeclaredFields(Class<?> fromClass, Class<?> stopWhenClass) {
        if (stopWhenClass == null) {
            stopWhenClass = Object.class;
        }
        List<Field> fields = new ArrayList<>();
        List<Class<?>> classes = new ArrayList<>();
        Class<?> cls = fromClass;
        do {
            classes.add(cls);
            cls = cls.getSuperclass();
        } while (cls != null && !cls.equals(stopWhenClass));
        for (int i = classes.size() - 1; i >= 0; i--) {
            fields.addAll(Arrays.asList(classes.get(i).getDeclaredFields()));
        }
        return fields;
    }
    public static Field getInheritedDeclaredField(Class<?> fromClass, String fieldName, Class<?> stopWhenClass) throws NoSuchFieldException {
        if (stopWhenClass == null) {
            stopWhenClass = Object.class;
        }
        Class<?> cls = fromClass;
        do {
            Field field;
            try {
                field = cls.getDeclaredField(fieldName);
                if (field != null) {
                    return field;
                }
            } catch (NoSuchFieldException | SecurityException e) {
                // Nothing. We'll try to get field from superclass
            }
            cls = cls.getSuperclass();
        } while (cls != null && !cls.equals(stopWhenClass));
        // If we got here, we'll throw an exception
        throw new NoSuchFieldException(fieldName);
    }
    public static Object getInheritedDeclaredFieldValue(Object obj, String fieldName, Class<?> stopWhenClass) throws NoSuchFieldException, IllegalAccessException {
        Field field = getInheritedDeclaredField(obj.getClass(), fieldName, stopWhenClass);
        field.setAccessible(true);
        return field.get(obj);
    }
}

Answer 4

您可以使用此代码简单地从任何类获取字段，无论它的父类或子类

for (Field field : YourClassName.class.getDeclaredFields()) {
  //fields
}