使用 Java 反射檢索繼承的屬性名稱/值

Question

我有一個 Java object 'ChildObj'，它是從 'ParentObj' 擴展而來的。 現在，是否可以使用 Java 反射機制檢索 ChildObj 的所有屬性名稱和值，包括繼承的屬性？

Class.getFields給了我公共屬性的數組， Class.getDeclaredFields給了我所有字段的數組，但它們都不包括繼承字段列表。

還有什么方法可以檢索繼承的屬性嗎？

Answer 1

不，你需要自己寫。 這是一個在Class.getSuperClass()上調用的簡單遞歸方法：

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

相反，如果您想依靠庫來完成此操作， Apache Commons Lang 3.2+ 版提供了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

您需要致電：

Class.getSuperclass().getDeclaredFields()

根據需要遞歸繼承層次結構。

Answer 5

使用反射庫：

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

Answer 6

遞歸解決方案是可以的，唯一的小問題是它們返回聲明和繼承成員的超集。 請注意， getDeclaredFields() 方法也返回私有方法。 因此，考慮到您在整個超類層次結構中導航，您將包括在超類中聲明的所有私有字段，而那些不會被繼承。

帶有 Modifier.isPublic || 的簡單過濾器 Modifier.isProtected 謂詞會做：

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

getFields()：獲取整個類層次結構中的所有公共字段並
getDeclaredFields()：獲取所有字段，無論它們的修飾符如何，但僅適用於當前類。 因此，您必須了解所涉及的所有層次結構。
我最近從org.apache.commons.lang3.reflect.FieldUtils看到了這段代碼

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 8

使用 spring util 庫，您可以使用檢查類中是否存在一個特定屬性：

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

log.info(field2.getName());

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

要么

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

 log.info(field2.getName());

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

@干杯

Answer 9

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“DidYouMeanThatTomHa...”解決方案的工作版本

Answer 10

你可以試試：

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

Answer 11

更短且實例化的對象更少？ ^^

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

Answer 12

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 13

這是對@user1079877 接受的答案的改寫。 它可能是一個不修改函數參數並且還使用一些現代 Java 功能的版本。

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);
    }
}

此實現還使調用更加簡潔：

var fields = getFields(MyType.class);

Answer 14

FieldUtils 沒有解決一些怪癖 - 特別是合成字段（例如由 JaCoCo 注入）以及 enum 類型課程對每個實例都有一個字段的事實，如果您正在遍歷對象圖，得到所有字段，然后獲取每個字段的字段等，然后當您點擊枚舉時將進入無限循環。 一個擴展的解決方案（老實說，我確信這必須存在於某個圖書館中！）將是：

/**
 * 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 中的測試類（並且 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

    }
}

Answer 15

我知道這是一個遲來的答案，但我只是把我的答案放在這里僅供我參考或任何對沒有反思的實現感興趣的人作為@dfa 答案的擴展；

public List<Field> getDeclaredFields(Class<?> tClass) {
    List<Field> fields = new LinkedList<>();

    while (tClass != null) {
        fields.addAll(Arrays.asList(tClass.getDeclaredFields()));
        tClass = tClass.getSuperclass();
    }

    return fields;
}