Java動態生成枚舉類型

工具類：

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

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;

public class DynamicEnumUtils {
    private static ReflectionFactory reflectionFactory = ReflectionFactory.getReflectionFactory();

    private static void setFailsafeFieldValue(Field field, Object target, Object value) throws NoSuchFieldException,
            IllegalAccessException {

        // 反射訪問私有變量
        field.setAccessible(true);

        /**
         * 接下來，我們將字段實例中的修飾符更改爲不再是final，
         * 從而使反射允許我們修改靜態final字段。
         */
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        int modifiers = modifiersField.getInt(field);

        // 去掉修飾符int中的最後一位
        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"); // Sun (Oracle?!?) JDK 1.5/6
        blankField(enumClass, "enumConstants"); // IBM JDK
    }

    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[] parms = new Object[additionalValues.length + 2];
        parms[0] = value;
        parms[1] = Integer.valueOf(ordinal);
        System.arraycopy(additionalValues, 0, parms, 2, additionalValues.length);
        return enumClass.cast(getConstructorAccessor(enumClass, additionalTypes).newInstance(parms));
    }

    /**
     * 將枚舉實例添加到作爲參數提供的枚舉類中
     *
     * @param enumType 要修改的枚舉類型
     * @param enumName 添加的枚舉類型名字
     * @param additionalTypes  枚舉類型參數類型列表
     * @param additionalValues 枚舉類型參數值列表
     * @param <T>
     */
    @SuppressWarnings("unchecked")
    public static <T extends Enum<?>> void addEnum(Class<T> enumType, String enumName, Class<?>[] additionalTypes, Object[] additionalValues) {

        // 0. 檢查類型
        if (!Enum.class.isAssignableFrom(enumType)) {
            throw new RuntimeException("class " + enumType + " is not an instance of Enum");
        }

        // 1. 在枚舉類中查找“$values”持有者並獲取以前的枚舉實例
        Field valuesField = null;
        Field[] fields = enumType.getDeclaredFields();
        for (Field field : fields) {
            if (field.getName().contains("$VALUES")) {
                valuesField = field;
                break;
            }
        }
        AccessibleObject.setAccessible(new Field[] { valuesField }, true);

        try {
            // 2. 將他拷貝到數組
            T[] previousValues = (T[]) valuesField.get(enumType);
            List<T> values = new ArrayList<T>(Arrays.asList(previousValues));

            // 3. 創建新的枚舉項
            T newValue = (T) makeEnum(enumType, enumName, values.size(), additionalTypes, additionalValues);

            // 4. 添加新的枚舉項
            values.add(newValue);

            // 5. 設定拷貝的數組，到枚舉類型
            setFailsafeFieldValue(valuesField, null, values.toArray((T[]) Array.newInstance(enumType, 0)));

            // 6. 清楚枚舉的緩存
            cleanEnumCache(enumType);
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage(), e);
        }
    }
}

測試類：

/**
 * 提現類型
 */
public enum WithdrawTypeEnum {
    /**
     * 單次
     */
    SINGLE_TIME("1", "單次"),
    MANY_TIMES("2", "多次");

    String code;
    String message;

    WithdrawTypeEnum(String code, String message) {
        this.code = code;
        this.message = message;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    private static final Map<String, WithdrawTypeEnum> codeToEnum = new HashMap<>();

    static {
        for (WithdrawTypeEnum one : WithdrawTypeEnum.values()) {
            codeToEnum.put(one.getCode(), one);
        }
    }

    public static Map<String, WithdrawTypeEnum> getCodeToEnum() {
        return codeToEnum;
    }

    public static String getName(String channel){
        if ("".equals(channel) || null == channel) {
            return "";
        } else {
            WithdrawTypeEnum productTypeEnum = WithdrawTypeEnum.getCodeToEnum().get( channel );
            String name = productTypeEnum.getMessage();
            return name;
        }
    }
}

未完，待續...