使用Java Reflection检索继承的属性名称/值

Question

我有一个Java对象'ChildObj'，它是从'ParentObj'扩展而来的。现在，如果可以使用Java反射机制检索ChildObj的所有属性名称和值，包括继承的属性？

Class.getFields为我提供了一系列公共属性，Class.getDeclaredFields为我提供了所有字段的数组，但没有一个包含继承的字段列表。

有没有办法检索继承的属性呢？

Answer 1

不，你需要自己写。这是一个简单的递归方法，名为Class.getSuperClass()：

public static List<Field> getAllFields(List<Field> fields, Class<?> type) {
    fields.addAll(Arrays.asList(type.getDeclaredFields()));

    if (type.getSuperclass() != null) {
        getAllFields(fields, type.getSuperclass());
    }

    return fields;
}

@Test
public void getLinkedListFields() {
    System.out.println(getAllFields(new LinkedList<Field>(), LinkedList.class));
}

Answer 2

    public static List<Field> getAllFields(Class<?> type) {
        List<Field> fields = new ArrayList<Field>();
        for (Class<?> c = type; c != null; c = c.getSuperclass()) {
            fields.addAll(Arrays.asList(c.getDeclaredFields()));
        }
        return fields;
    }

Answer 3

如果您希望依靠库来实现此目的，Apache Commons Lang版本3.2+提供了FieldUtils.getAllFieldsList：

import java.lang.reflect.Field;
import java.util.AbstractCollection;
import java.util.AbstractList;
import java.util.AbstractSequentialList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

import org.apache.commons.lang3.reflect.FieldUtils;
import org.junit.Assert;
import org.junit.Test;

public class FieldUtilsTest {

    @Test
    public void testGetAllFieldsList() {

        // Get all fields in this class and all of its parents
        final List<Field> allFields = FieldUtils.getAllFieldsList(LinkedList.class);

        // Get the fields form each individual class in the type's hierarchy
        final List<Field> allFieldsClass = Arrays.asList(LinkedList.class.getFields());
        final List<Field> allFieldsParent = Arrays.asList(AbstractSequentialList.class.getFields());
        final List<Field> allFieldsParentsParent = Arrays.asList(AbstractList.class.getFields());
        final List<Field> allFieldsParentsParentsParent = Arrays.asList(AbstractCollection.class.getFields());

        // Test that `getAllFieldsList` did truly get all of the fields of the the class and all its parents 
        Assert.assertTrue(allFields.containsAll(allFieldsClass));
        Assert.assertTrue(allFields.containsAll(allFieldsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParent));
        Assert.assertTrue(allFields.containsAll(allFieldsParentsParentsParent));
    }
}

Answer 4

您需要致电：

Class.getSuperclass().getDeclaredFields()

根据需要递归继承层次结构。

Answer 5

使用Reflections库：

public Set<Field> getAllFields(Class<?> aClass) {
    return org.reflections.ReflectionUtils.getAllFields(aClass);
}

Answer 6

递归解决方案没问题，唯一的小问题是它们返回已声明和继承成员的超集。请注意，getDeclaredFields（）方法也返回私有方法。因此，只要您导航整个超类层次结构，就会包含在超类中声明的所有私有字段，而这些字段不会被继承。

带Modifier.isPublic ||的简单过滤器Modifier.isProtected谓词可以：

import static java.lang.reflect.Modifier.isPublic;
import static java.lang.reflect.Modifier.isProtected;

(...)

List<Field> inheritableFields = new ArrayList<Field>();
for (Field field : type.getDeclaredFields()) {
    if (isProtected(field.getModifiers()) || isPublic(field.getModifiers())) {
       inheritableFields.add(field);
    }
}

Answer 7

使用spring util库，您可以用来检查类中是否存在一个特定属性：

Field field = ReflectionUtils.findRequiredField(YOUR_CLASS.class, "ATTRIBUTE_NAME");

log.info(field2.getName());

Api文档：
https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/util/ReflectionUtils.html

或

 Field field2 = ReflectionUtils.findField(YOUR_CLASS.class, "ATTRIBUTE_NAME");

 log.info(field2.getName());

Api文档：
https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/util/ReflectionUtils.html

@欢呼声

Answer 8

private static void addDeclaredAndInheritedFields(Class<?> c, Collection<Field> fields) {
    fields.addAll(Arrays.asList(c.getDeclaredFields())); 
    Class<?> superClass = c.getSuperclass(); 
    if (superClass != null) { 
        addDeclaredAndInheritedFields(superClass, fields); 
    }       
}

上面的“DidYouMeanThatTomHa ...”解决方案的工作版本

Answer 9

您可以尝试：

   Class parentClass = getClass().getSuperclass();
   if (parentClass != null) {
      parentClass.getDeclaredFields();
   }

Answer 10

更短且实例化的对象更少？ ^^

private static Field[] getAllFields(Class<?> type) {
    if (type.getSuperclass() != null) {
        return (Field[]) ArrayUtils.addAll(getAllFields(type.getSuperclass()), type.getDeclaredFields());
    }
    return type.getDeclaredFields();
}

Answer 11

private static void addDeclaredAndInheritedFields(Class c, Collection<Field> fields) {
    fields.addAll(Arrays.asList(c.getDeclaredFields()));
    Class superClass = c.getSuperclass();
    if (superClass != null) {
        addDeclaredAndInheritedFields(superClass, fields);
    }
}

Answer 12

这是@ user1079877接受的答案的改写。该版本可能不会修改函数的参数，但也会使用一些现代Java功能。

public <T> Field[] getFields(final Class<T> type, final Field... fields) {
    final Field[] items = Stream.of(type.getDeclaredFields(), fields).flatMap(Stream::of).toArray(Field[]::new);
    if (type.getSuperclass() == null) {
        return items;
    } else {
        return getFields(type.getSuperclass(), items);
    }
}

此实现还使调用更加简洁：

var fields = getFields(MyType.class);

Answer 13

我最近从org.apache.commons.lang3.reflect.FieldUtils

看到了这段代码

public static List<Field> getAllFieldsList(final Class<?> cls) {
        Validate.isTrue(cls != null, "The class must not be null");
        final List<Field> allFields = new ArrayList<>();
        Class<?> currentClass = cls;
        while (currentClass != null) {
            final Field[] declaredFields = currentClass.getDeclaredFields();
            Collections.addAll(allFields, declaredFields);
            currentClass = currentClass.getSuperclass();
        }
        return allFields;
}

Answer 14

FieldUtils并没有解决一些奇怪的问题-特别是合成字段（例如JaCoCo注入的字段），以及枚举类型当然对每个实例都有一个字段，并且如果您遍历一个对象的事实图，获取所有字段，然后获取每个字段的字段，等等，然后当您遇到枚举时，您将陷入无限循环。扩展的解决方案（老实说，我确定它必须存在于某个地方的库中！）将是：

/**
 * Return a list containing all declared fields and all inherited fields for the given input
 * (but avoiding any quirky enum fields and tool injected fields).
 */
public List<Field> getAllFields(Object input) {
    return getFieldsAndInheritedFields(new ArrayList<>(), input.getClass());
}

private List<Field> getFieldsAndInheritedFields(List<Field> fields, Class<?> inputType) {
    fields.addAll(getFilteredDeclaredFields(inputType));
    return inputType.getSuperclass() == null ? fields : getFieldsAndInheritedFields(fields, inputType.getSuperclass());

}

/**
 * Where the input is NOT an {@link Enum} type then get all declared fields except synthetic fields (ie instrumented
 * additional fields). Where the input IS an {@link Enum} type then also skip the fields that are all the
 * {@link Enum} instances as this would lead to an infinite loop if the user of this class is traversing
 * an object graph.
 */
private List<Field> getFilteredDeclaredFields(Class<?> inputType) {
    return Arrays.asList(inputType.getDeclaredFields()).stream()
                 .filter(field -> !isAnEnum(inputType) ||
                         (isAnEnum(inputType) && !isSameType(field, inputType)))
                 .filter(field -> !field.isSynthetic())
                 .collect(Collectors.toList());

}

private boolean isAnEnum(Class<?> type) {
    return Enum.class.isAssignableFrom(type);
}

private boolean isSameType(Field input, Class<?> ownerType) {
    return input.getType().equals(ownerType);
}

Spock中的测试类（Groovy添加了合成字段）：

class ReflectionUtilsSpec extends Specification {

    def "declared fields only"() {

        given: "an instance of a class that does not inherit any fields"
        def instance = new Superclass()

        when: "all fields are requested"
        def result = new ReflectionUtils().getAllFields(instance)

        then: "the fields declared by that instance's class are returned"
        result.size() == 1
        result.findAll { it.name in ['superThing'] }.size() == 1
    }


    def "inherited fields"() {

        given: "an instance of a class that inherits fields"
        def instance = new Subclass()

        when: "all fields are requested"
        def result = new ReflectionUtils().getAllFields(instance)

        then: "the fields declared by that instance's class and its superclasses are returned"
        result.size() == 2
        result.findAll { it.name in ['subThing', 'superThing'] }.size() == 2

    }

    def "no fields"() {
        given: "an instance of a class with no declared or inherited fields"
        def instance = new SuperDooperclass()

        when: "all fields are requested"
        def result = new ReflectionUtils().getAllFields(instance)

        then: "the fields declared by that instance's class and its superclasses are returned"
        result.size() == 0
    }

    def "enum"() {

        given: "an instance of an enum"
        def instance = Item.BIT

        when: "all fields are requested"
        def result = new ReflectionUtils().getAllFields(instance)

        then: "the fields declared by that instance's class and its superclasses are returned"
        result.size() == 3
        result.findAll { it.name == 'smallerItem' }.size() == 1
    }

    private class SuperDooperclass {
    }

    private class Superclass extends SuperDooperclass {
        private String superThing
    }


    private class Subclass extends Superclass {
        private String subThing
    }

    private enum Item {

        BIT("quark"), BOB("muon")

        Item(String smallerItem) {
            this.smallerItem = smallerItem
        }

        private String smallerItem

    }
}