枚举修改工具类

该类可以实现动态添加枚举值。

这个类的实现是我从网上淘来的，这里留个备份。

代码如下:

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import sun.reflect.ConstructorAccessor;
import sun.reflect.FieldAccessor;
import sun.reflect.ReflectionFactory;

/**
 * @author littleRabbit on 2020-09-25
 * detail：
 */
public class EnumUtils {

    private static ReflectionFactory reflectionFactory = ReflectionFactory.getReflectionFactory();

    private static void setFailsafeFieldValue(Field field, Object target, Object value) throws NoSuchFieldException,
            IllegalAccessException {
        field.setAccessible(true);
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        int modifiers = modifiersField.getInt(field);
        modifiers &= ~Modifier.FINAL;
        modifiersField.setInt(field, modifiers);
        FieldAccessor fa = reflectionFactory.newFieldAccessor(field, false);
        fa.set(target, value);
    }

    private static void blankField(Class<?> enumClass, String fieldName) throws NoSuchFieldException,
            IllegalAccessException {
        for (Field field : Class.class.getDeclaredFields()) {
            if (field.getName().contains(fieldName)) {
                AccessibleObject.setAccessible(new Field[] { field }, true);
                setFailsafeFieldValue(field, enumClass, null);
                break;
            }
        }
    }

    private static void cleanEnumCache(Class<?> enumClass) throws NoSuchFieldException, IllegalAccessException {
        blankField(enumClass, "enumConstantDirectory");
        blankField(enumClass, "enumConstants");
    }

    private static ConstructorAccessor getConstructorAccessor(Class<?> enumClass, Class<?>[] additionalParameterTypes)
            throws NoSuchMethodException {
        Class<?>[] parameterTypes = new Class[additionalParameterTypes.length + 2];
        parameterTypes[0] = String.class;
        parameterTypes[1] = int.class;
        System.arraycopy(additionalParameterTypes, 0, parameterTypes, 2, additionalParameterTypes.length);
        return reflectionFactory.newConstructorAccessor(enumClass.getDeclaredConstructor(parameterTypes));
    }

    private static Object makeEnum(Class<?> enumClass, String value, int ordinal, Class<?>[] additionalTypes,
                                   Object[] additionalValues) throws Exception {
        Object[] params = new Object[additionalValues.length + 2];
        params[0] = value;
        params[1] = Integer.valueOf(ordinal);
        System.arraycopy(additionalValues, 0, params, 2, additionalValues.length);
        return enumClass.cast(getConstructorAccessor(enumClass, additionalTypes).newInstance(params));
    }

    @SuppressWarnings("unchecked")
    public static <T extends Enum<?>> void addEnum(Class<T> enumType, String enumName, Class<?>[] additionalTypes, Object[] additionalValues) {
        if (!Enum.class.isAssignableFrom(enumType)) {
            throw new RuntimeException("class " + enumType + " is not an instance of Enum");
        }
        Field valuesField = null;
        Field[] fields = enumType.getDeclaredFields();
        for (Field field : fields) {
            if (field.getName().contains("$VALUES")) {
                valuesField = field;
                break;
            }
        }
        AccessibleObject.setAccessible(new Field[] { valuesField }, true);
        try {
            T[] previousValues = (T[]) valuesField.get(enumType);
            List<T> values = new ArrayList<T>(Arrays.asList(previousValues));
            T newValue = (T) makeEnum(enumType, enumName, values.size(), additionalTypes, additionalValues);
            values.add(newValue);
            setFailsafeFieldValue(valuesField, null, values.toArray((T[]) Array.newInstance(enumType, 0)));
            cleanEnumCache(enumType);
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage(), e);
        }
    }
}

测试代码：

public static void main(String[] args) {
    Class<?>[] additionalTypes = new Class<?>[]{String.class, int.class};
    Object[] additionalValues = new Object[] {"小猪猪", 50};
    EnumUtils.addEnum(Animal.class, "Pig", additionalTypes, additionalValues);
    Arrays.stream(Animal.values()).forEach(animal -> {
        System.out.println("name=" + animal.getName() + ", score=" + animal.getScore());
    });
}

结果如下：

Animal.java

/**
 * @author littleRabbit on 2020-09-25
 * detail：
 */
public enum Animal {

    RABBIT("小兔兔", 100),

    DOG("小狗狗", 90),

    CAT("小猫猫", 80);

    Animal(String name, int score) {
        this.name = name;
        this.score = score;
    }

    private String name;

    private int score;

    public String getName() {
        return name;
    }

    public int getScore() {
        return score;
    }
}