动态改变枚举类的枚举值，配置方式实现枚举

╰+攻爆jí腚メ 2024-04-17 23:02 72阅读 0赞

> ### 背景 ###

生产环境中需要枚举类来定义一些常量，但是又希望不用修改代码来新增这些常量。

修改代码又涉及到版本发布，特别麻烦，于是想着通过配置文件的方式来实现枚举项的改变

> ### 代码结构 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW4xMDc4NzY_size_16_color_FFFFFF_t_70][]

### 接下来逐个类看看 ###

> ### TestEnum，枚举类，初始化是空的 ###

package com.xiong.test.dynamicenum;
    
    /**
     * 枚举
     */
    public enum TestEnum {
        ;
    
        String code;
        String name;
    
        TestEnum(String code, String name) {
            this.code = code;
            this.name = name;
        }
    
        public String getCode() {
            return code;
        }
    
        public String getName() {
            return name;
        }
    
        @Override
        public String toString() {
            return this.name() + "{" +
                    "code='" + code + '\'' +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

> ### DynamicEnumUtil，核心类，这个类无需修改，直接用即可，对外接口  ###
> 
> ### DynamicEnumUtil.addEnum(） ###

package com.xiong.test.dynamicenum;
    
    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;
    
    /**
     * 动态新增枚举工具类
     */
    public class DynamicEnumUtil {
        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"); // 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));
        }
    
        /**
         * 判断枚举是否已存在
         * @param values
         * @param enumName
         * @param <T>
         * @return
         */
        public static <T extends Enum<?>> boolean contains(List<T> values, String enumName){
            for (T value : values) {
                if (value.name().equals(enumName)) {
                    return true;
                }
            }
            return false;
        }
    
    
        /**
         * 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, Class<?>[] additionalTypes, Object[] additionalValues) {
    
            // 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, enumName, values.size(), additionalTypes, additionalValues);
    
                if(contains(values,enumName)){
                    System.out.println("Enum：" + enumName + " 已存在");
                    return;
                }
    
                // 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);
            }
        }
    
    
    }

> ### 测试一下 ###

package com.xiong.test.dynamicenum;
    
    public class MainTest {
        public static void main(String[] args) {
    
            // 新增四个枚举项
            addTestEnum("a", "A", "AA");
            addTestEnum("b", "B", "BB");
            addTestEnum("c", "C", "CC");
            addTestEnum("d", "D", "DD");
    
            
            for (TestEnum testEnum : TestEnum.values()) {
                System.out.println(testEnum.toString());
            }
    
        }
    
        /**
         * 
         * @param enumName 枚举名
         * @param code 枚举项1
         * @param name 枚举项2
         */
        private static void addTestEnum(String enumName, String code, String name) {
            DynamicEnumUtil.addEnum(TestEnum.class, enumName, new Class<?>[]
                    {String.class, String.class},
                    new Object[]{code, name});
        }
    }

> ### 输出结果，证明是可以加上枚举项的 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW4xMDc4NzY_size_16_color_FFFFFF_t_70 1][]

## 接下来是从配置读取枚举内容，然后服务启动加上自定义枚举项 ##

使用的是spring boot 的环境，spring 启动的时候完成加载

新建一个DynamicEnumloadService，实现InitializingBean ，这样在spring 加载bean的时候自动调用 afterPropertiesSet  方法，

我把枚举项的动态新增放在该方法里面，完成自动注入。

> ### DynamicEnumloadService ###

package com.xiong.test.dynamicenum;
    
    
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.stereotype.Service;
    
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.InputStreamReader;
    import java.util.Enumeration;
    import java.util.Properties;
    import java.util.logging.Logger;
    
    @Service
    public class DynamicEnumloadService implements InitializingBean {
    
        private static Logger logger = Logger.getLogger("");
        @Override
        public void afterPropertiesSet() {
    
            InputStream inputStream = DynamicEnumloadService.class.getResourceAsStream("/application.properties");
            //实例化Properties类
            Properties properties = new Properties();
            //调用load()方法加载properties文件，load里面传入InputSteam类型的参数或者Reader类型的参数
            try {
                properties.load(new InputStreamReader(inputStream,"UTF-8"));
            } catch (IOException e) {
                logger.info("TestEnum 动态枚举加载失败......");
                e.printStackTrace();
            }
    
            Enumeration em = properties.propertyNames();
            while (em.hasMoreElements()) {
                String key = (String) em.nextElement();
                String value = properties.getProperty(key);
                String[] split = value.split("\\|");
                addTestEnum(key, split);
            }
    
            logger.info("TestEnum 动态枚举加载成功......");
            for (TestEnum testEnum : TestEnum.values()) {
                logger.info(testEnum.toString());
            }
    
        }
    
        /**
         * 新增 TestEnum 枚举项
         *
         * @param enumName 枚举 名称
         * @param objects 枚举项
         */
        private static void addTestEnum(String enumName, Object[] objects) {
            DynamicEnumUtil.addEnum(TestEnum.class, enumName, new Class<?>[]
                    {String.class, String.class}, objects);
        }
    }

> ### application.properties ###

tanenum = test1|tan
    zhannum = test2|zhan

### 然后启动服务看看。。 ###

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW4xMDc4NzY_size_16_color_FFFFFF_t_70 2][]

### 完美。。 ###

### 这样在服务的其他地方就可以使用这个枚举类了。如果枚举的内容有变动，只需要改配置文件，把服务重启即可，不用重新改代码。 ###

感谢：[https://www.cnblogs.com/lhp2012/p/9337207.html][https_www.cnblogs.com_lhp2012_p_9337207.html]

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW4xMDc4NzY_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/b4bd8e65a33e4cb5b8637abb3840d8de.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poYW4xMDc4NzY_size_16_color_FFFFFF_t_70 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/17/7add7b9aae38456ea13c5fecf8658bdb.png
[https_www.cnblogs.com_lhp2012_p_9337207.html]: https://www.cnblogs.com/lhp2012/p/9337207.html