工作中遇到需要对枚举类的值进行动态更新 手动改不现实也不方便 现记录下来方便以后学习使用

1.在工程utils包中添加动态更新枚举类得工具类(根据自己得项目，放到指定位置调用就可以)

2.一开始陷入了误区，认为要根据我自己得枚举类去修改，addEnum和makeEnum方法因为网上示例都是两个参数得，

而我的是5个的，弄了好久(被自己蠢晕)才发现，它是个数组啊。

package com.genju.ziji.dexiangmu.util;

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

* @return

*/

public static > boolean contains(List 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 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 > void addEnum(Class 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 values = new ArrayList(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);

}

}

}

3.测试

public static void main(String args[]) {

addEnum("1","2","3","4","5");

for(SubBank e : SunBank.values()){

System.out.println(e.getBankName());

}

}

private static void addEnum(String enumName,String id,String name,String desc,AreaType 　　　　　　areaType,List> paramTypes){

DynamicEnumUtil.addEnum(Subank.class,enumName,

new Class>[]{Stirng.class,String.class,AreaType.class,List.Class},

new object[]{id,nae,desc,areaType,paramTypes});

}

最后打印看效果是ok得可以添加上，我这里是将枚举类直接写上，有需要的也可以根据自己得需求做成动态的；

如有不准确得地方欢迎指点