java动态更新枚举类

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 <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);
}
}

}

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<Class<? extends Enum>> 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

posted @ 2019-09-16 15:20  KpGo  阅读(2311)  评论(0编辑  收藏