在某些场景下我们需要动态生成一些枚举值，主要是通过反射生成，但是这种生成枚举值是不能switch的
以下是代码案例：
1.枚举值类
public enum CodeInfoEnum {
LOCK(1L, 1L, "LOCK_TYPE", "LOCK"), UNLOCK(1L, 2L, "LOCK_TYPE", "LOCK");
public Long classId;
public Long infoId;
public String classCode;
public String infoCode;
CodeInfoEnum(Long classId, Long infoId, String classCode, String infoCode) {
this.classId = classId;
this.infoId = infoId;
this.classCode = classCode;
this.infoCode = infoCode;
}
public static CodeInfoEnum getByInfoId(Long infoId) {
return CodeInfoEnum.valueOf(infoId + "");
}
public static List<CodeInfoEnum> getByClassId(Long classId) {
return Arrays.stream(CodeInfoEnum.values()).filter(item -> item.classId.equals(classId)).collect(Collectors.toList());
}
public static CodeInfoEnum getByClassCodeAndInfoCode(String classCode, String infoCode) {
Optional<CodeInfoEnum> opt = Arrays.stream(CodeInfoEnum.values()).filter(item -> item.classCode.equals(classCode) && item.infoCode.equals(infoCode)).findFirst();
return opt.orElse(null);
}
@Override
public String toString() {
return "CodeInfoEnum{" +
"classId=" + classId +
", infoId=" + infoId +
", classCode=‘" + classCode + ‘\‘‘ +
", infoCode=‘" + infoCode + ‘\‘‘ +
‘}‘;
}
}
2.生成工具类
public class DynamicEnumTest {
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<?>[] paramClass,Object[] paramValue) {
// 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
paramClass,
//new Object[] {}
paramValue
); // could be used to pass values to the enum constuctor if needed
// 4. add new value
values.add(newValue);
Object object=values.toArray((T[]) Array.newInstance(enumType, 0));
// 5. Set new values field
setFailsafeFieldValue(valuesField, null, object);
// 6. Clean enum cache
cleanEnumCache(enumType);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e.getMessage(), e);
}
}
public static void main(String[] args) {
//
synchronized (CodeInfoEnum.class) {
addEnum(CodeInfoEnum.class, "3", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{2L, 3L, "ActiveStatus", "Active"});
addEnum(CodeInfoEnum.class, "4", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{2L, 4L, "ActiveStatus", "Inactive"});
addEnum(CodeInfoEnum.class, "5", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{3L, 5L, "Optype", "OP1"});
addEnum(CodeInfoEnum.class, "6", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{3L, 6L, "Optype", "OP2"});
addEnum(CodeInfoEnum.class, "7", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{3L, 7L, "Optype", "OP3"});
addEnum(CodeInfoEnum.class, "8", new Class<?>[]{Long.class, Long.class, String.class, String.class}, new Object[]{3L, 8L, "Optype", "OP4"});
}
CodeInfoEnum codeInfoEnum =CodeInfoEnum.valueOf("5");
System.out.println(codeInfoEnum);
// Run a few tests just to show it works OK.
System.out.println(Arrays.deepToString(CodeInfoEnum.values()));
System.out.println("============================打印所有枚举（包括固定的和动态的），可以将数据库中保存的CIC以枚举的形式加载到JVM");
for(CodeInfoEnum codeInfo:CodeInfoEnum.values()){
System.out.println(codeInfo.toString());
}
System.out.println("============================通过codeId找到的枚举，用于PO转VO的处理");
CodeInfoEnum activeStatus_Active = CodeInfoEnum.getByInfoId(3L);
System.out.println(activeStatus_Active);
System.out.println("============================通过ClassId找到的枚举列表");
List<CodeInfoEnum> activeStatusEnumList = CodeInfoEnum.getByClassId(3L);
for(CodeInfoEnum codeInfo : activeStatusEnumList){
System.out.println(codeInfo);
}
System.out.println("============================通过ClassCode和InfoCode获取枚举，用于导入验证CIC合法性");
CodeInfoEnum toGetActiveStatus_Active = CodeInfoEnum.getByClassCodeAndInfoCode("ActiveStatus","Active");
System.out.println(toGetActiveStatus_Active);
System.out.println("============================通过ClassCode和InfoCode获取枚举，输入不存在的Code，则返回NULL");
CodeInfoEnum toGetActiveStatus_miss = CodeInfoEnum.getByClassCodeAndInfoCode("ActiveStatus","MISS");
System.out.println(toGetActiveStatus_miss);
}
}
原文：https://www.cnblogs.com/sn-wu-z/p/14080675.html