Question

我有一个枚举：

public enum Language {
    EN_GB("en-gb"),
    EN_DE("en-de"),
    DE_DE("de-de");

    private final String text;

    Language(final String text) {
        this.text = text;
    }

    @JsonValue
    public String getValue() {
        return text;
    }
}

我有一个用于枚举转换的类：

public class EnumConverter {

    private static ReflectionFactory reflectionFactory = 
    ReflectionFactory.getReflectionFactory();

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

        // let's make the field accessible
        field.setAccessible(true);

        // next we change the modifier in the Field instance to
        // not be final anymore, thus tricking reflection into
        // letting us modify the static final field
        Field modifiersField = Field.class.getDeclaredField("modifiers");
        modifiersField.setAccessible(true);
        int modifiers = modifiersField.getInt(field);

        // blank out the final bit in the modifiers int
        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");
    }

    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));
    }

    /**
     * Add an enum instance to the enum class given as argument
     *  @param <T> the type of the enum (implicit)
     * @param enumType the class of the enum to be modified
     * @param enumName the name of the new enum instance to be added to the class.
     */
    @SuppressWarnings("unchecked")
    public static <T extends Enum<?>> void addEnum( Class<T> enumType, String enumName) {

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

        // 1. Lookup "$VALUES" holder in enum class and get previous enum instances
        Field valuesField = null;
        Field[] fields = enumType.getDeclaredFields();
        for (Field field : fields) {
            if (field.getName().contains("$VALUES")) {
                valuesField = field;
                break;
            }
        }
        AccessibleObject.setAccessible(new Field[] { valuesField }, true);

        try {

            // 2. Copy it
            T[] previousValues = (T[]) valuesField.get(enumType);
            List<T> values = new ArrayList<T>(Arrays.asList(previousValues));

            // 3. build new enum
            T newValue = (T) makeEnum(enumType, // The target enum class
                    enumName, // THE NEW ENUM INSTANCE TO BE DYNAMICALLY ADDED
                    values.size(),
                    new Class<?>[] {}, // could be used to pass values to the enum constuctor if needed
                    new Object[] {}); // could be used to pass values to the enum constuctor if needed

            // 4. add new value
            values.add(newValue);

            // 5. Set new values field
            setFailsafeFieldValue(valuesField, null, values.toArray((T[]) Array.newInstance(enumType, 0)));

            // 6. Clean enum cache
            cleanEnumCache(enumType);

        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e.getMessage(), e);
        }
    }
}

我得到例外

java.lang.NoSuchMethodException: com.staxter.models.response.auth.Language.<init>(java.lang.String, int) at java.lang.Class.getConstructor0(Class.java:3082) at java.lang.Class.getDeclaredConstructor(Class.java:2178) at com.staxter.utility.EnumConverter.getConstructorAccessor(EnumConverter.java:61) at com.staxter.utility.EnumConverter.makeEnum(EnumConverter.java:70) at com.staxter.utility.EnumConverter.addEnum(EnumConverter.java:105)

java.lang.RuntimeException: com.staxter.models.response.auth.Language.<init>(java.lang.String, int) at com.staxter.utility.EnumConverter.addEnum(EnumConverter.java:122)

所以我的问题是：
为什么会出现这种异常以及我应该在enumConverter类中进行哪些编辑？

P.S。如果我从枚举中删除所有字符串参数和方法，则没有异常，并且测试成功。但是我需要字符串参数。

Answer 1

如果我正确理解了您的问题。您想从String实例获取枚举类型。

要解决此问题，您不需要单独的类。
您可以使用静态方法：

public enum Language {
    EN_GB("en-gb"),
    EN_DE("en-de"),
    DE_DE("de-de");

    private final String text;

    Language(final String text) {
        this.text = text;
    }

    @JsonValue
    public String getValue() {
        return text;
    }

    public static Language fromString(String str) {
        for (Language lang : Language.values()) {
            if (lang.getValue().equalsIgnoreCase(str)) {
                return lang;
            }
        }
        throw new IllegalArgumentException("Illegal enum parameter: " + str);
    }

    public static void main(String[] args) {
        System.out.println(Language.fromString("en-de"));
        System.out.println(Language.fromString("en-gb"));
        System.out.println(Language.fromString("en-dd"));
    }
}

输出：

EN_DE
EN_GB
Exception in thread "main" java.lang.IllegalArgumentException: Illegal enum parameter: en-dd
    at com.tribe.pdf2data.pdf2data.dto.Language.fromString(Language.java:27)
    at com.tribe.pdf2data.pdf2data.dto.Language.main(Language.java:33)

Answer 2

将工厂方法添加到您的枚举。 Jackson 将调用此方法以反序列化您的枚举。

public enum Language {
    // ...

    @JsonCreator
    public static Language parseId(String text) {
        for (Lanugage language : values())
            if (language.text.equalsIgnoreCase(text))
                return language;

        throw new EnumConstantNotPresentException(Language.class, text);
    }
}

或者，您可以为此枚举声明自定义反序列化器。

Answer 3

更新 我选择使用Locale类。这对我来说更合适，并且我的项目也不会困难。谢谢您的提示，伙计们！

无法将String转换为enumType

3 个答案: