动态生成enum(dynamic enum)

因为以前的老代码定义了enum类，而这部分代码是作为公共的jar,修改时会影响很大,所以希望动态添加枚举属性

首先是一个工具类DynamicEnumUtil ，参考网上的：

原文链接：

http://bbs.csdn.net/topics/391037532

https://www.niceideas.ch/roller2/badtrash/entry/java_create_enum_instances_dynamically

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 com.**.enums.Carrier;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);       }   }   public static void main(String[] args) {      System.out.println(Arrays.deepToString(Carrier.values()));       // Dynamically add 1 instance       addEnum(Carrier.class,"test60",new Class[]{int.class,String.class, String.class}, new Object[]{60, "test60","CHINA"});       addEnum(Carrier.class,"test60",new Class[]{int.class,String.class, String.class}, new Object[]{60, "test60","CHINA"});       // Run a few tests just to show it works OK.       System.out.println(Arrays.deepToString(Carrier.values()));       Carrier[] carriers = Carrier.values();       System.out.println(carriers[1].getId());   }   }

枚举类Carrier里包含三个属性：

public enum Carrier implements Serializable{     UNKNOWN(0,"",""),    AIRCEL(1,"Aircel","IN"),  .....    private int id;    private String name;    private String country;....}

然后定义了一个schedule每5分钟去数据库查找是否有新的carrier信息，如果有添加新的enum属性

public class CarrierLoader {private static final int RELOAD_PERIOD = 5 * 60 * 1000;//5 mins    private static int i=0;static {//checkNewCarrier();new Timer(true).schedule(new TimerTask() {public void run() {try {System.out.println("runner ---------------");checkNewCarrier();if(i<60) i++;} catch (Exception e) {e.printStackTrace();}}}, RELOAD_PERIOD, RELOAD_PERIOD);}    public static void checkNewCarrier(){    Map<Integer, CarrierBean> carriers = DBUtil.loadCarrier();//query carriers from DBList<CarrierBean> newCarriers = new ArrayList<CarrierBean>();for(int id:carriers.keySet()){                          if(!Carrier.getCarrierMap().keySet().contains(id)){//add new carrier to newCarriersnewCarriers.add(carriers.get(id));}}if(newCarriers!=null && newCarriers.size()>0){for(CarrierBean carrier:newCarriers){System.out.println("add new carrier:"+carrier.getId());DynamicEnumUtil.addEnum(Carrier.class, carrier.getName(), new Class[]{int.class,String.class, String.class}, new Object[]{carrier.getId(), carrier.getName(),carrier.getCountry()});}Carrier.initCarrierMap();//reset the carrierMap}else{System.out.println("no new carrier");System.out.println("get carrier fromid="+i+"------"+Carrier.fromInt(i));}    }public static void main(String[] args) {System.out.println("get carrier fromid=4###ID="+Carrier.fromInt(4).getId()+"##NAME="+Carrier.fromInt(4).getName()+"##COUNTRY="+Carrier.fromInt(4).getCountry());}}

本文参考：

http://bbs.csdn.net/topics/391037532

https://www.niceideas.ch/roller2/badtrash/entry/java_create_enum_instances_dynamically