DynamicEnumUtil 动态添加枚举类的枚举值

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;

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

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));
   }

   /**
    * 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);

           // 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);
       }
   }

}

　　

测试类

import java.lang.reflect.Field;

public class MainTest {
    private static enum TestEnum {
        a(111,"AAA"),
        b(222,"BBB"),
        c(333,"CCC");

        private int value;
        private String text;
        TestEnum(int value,String text){
            this.value = value;
            this.text = text;
        }

        public int getValue() {
            return value;
        }

        public void setValue(int value) {
            this.value = value;
        }

        public String getText() {
            return text;
        }

        public void setText(String text) {
            this.text = text;
        }

        @Override
        public String toString() {
            return "TestEnum{" +
                    "value=" + value +
                    ", text='" + text + '\'' +
                    '}';
        }
    };

    private static void addTestEnum(String enumName,int value,String text){
        DynamicEnumUtil.addEnum(TestEnum.class,enumName,new Class<?>[] {int.class,String.class},new Object[] {value,text});
    }

    public static void main(String[] args) {

        addTestEnum("d",444,"DDD");
        addTestEnum("e",555,"EEE");
        addTestEnum("f",666,"FFF");
        addTestEnum("g",777,"GGG");

        for (TestEnum testEnum:TestEnum.values()){
            System.out.println(testEnum.toString());
        }

        Class<TestEnum> ccc = TestEnum.class;
        Field[] fff = ccc.getDeclaredFields();
        TestEnum testEnum = TestEnum.b;
        switch (testEnum){
            case a:{
                System.out.println("22222reefwsfsds");
                break;
            }
            case b:
                System.out.println("bbb");
                break;
        }

    }
}